BEHAVIORAL ECOLOGY OF YOUNG AMERICAN ALLIGATORS By DAVID CHARLES DEITZ A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1979 ACKNOWLEDGEMENTS It is a pleasure to acknowledge my committee chairman, A. F. Carr, Jr., and my supervisory committee, W. Auffenberg, J. H. Kaufiaann and D. A. Dewsbury, for their advice, encouragement and patience from the beginning of this study. Special thanks are due to Tommy Hines for his constant support, criticism and invaluable companionship in the fiel H. W. Campbell has also contributed many worthwhile ideas and criticisms throughout the study, for which | am most grateful. Financial support was provided by a grant from the Division of Sponsored Research of the University of Florida to Ww. Auffenbers; technical and iogistical help as well as additional financial suproort was derated by the Fiorida Game and Fresh Water Fish Commission. The Florida Department of Natural Resources permitted access to Payne's feld assistance are too numerous to bh property. Those who provided thank individually, but | owe special appreciation for the efforts of R. Ashton, S. Ganci, T. Goodwin, 9. Jackson, K. Prestwich, ©. A. Ross, M. Salzburg, D. Simmons, and A. Woodward. ?. Murphy generously made her equipment at the.Savannah River Ecology Laboratory available, and assisted with my experiments there. a] w cussions with T. Joanen, L. McNease and 7. Murony at the inception of the study were extramely helpful, and regular exchance of ideas with H. Hunt, J. and M. Kushian, and C. ; eo fa) n wn = a: rt) w cr 3 c ‘ iating throughout. L. 2. Franz, J. and M. Kuskh!an ana 3. Rodda allowed me to use their unpublished data. M. Conlon assisted with the data analysis and E. Belcher prepared the figures. Finally, ! thank 2. Gillis for her expert typing and editorial advice, and my wife, Joan Spiegel, for encouragement and assistance with the manuscript. TABLE OF CONTENTS ACKNOWLEDGEMENTS. ABSTRACT. CHAPTER | INTRODUCTION. 11 STUDY AREAS Orange and Lochloosa Lakes. Payne's Prairie Lake Griffin. Station Pond. Vil GROWTH, MORTALITY AND MOVEMENTS OF JUVENILE ALLIGATORS, Introduetion. « . . @ « » « Methods i RESUTES «6 & 6 ww Sd» bw a S @ SG & Koes bo we Discussion. 1V SOCIAL BEHAVIOR OF JUVENILE ALLIGATORS. introduction. Methods Resuits Discussion. V EXPERIMENTAL ANALYSIS OF THE VOCALIZATIONS OF JUVENILE ALLIGATORS introduction. Methods Results DISCUSSIONS « . a2 ws @ 2 et ewe & ee eS \| SUMMARY ANG CONCLUS!ONS Oo wWn—-— w MOO Gs Or. ON hd Gv b- UW S PND: eer aes wens 1 CO ho we an Abstract of Dissertation Presented to the Graduate Counci] of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy BEHAVIORAL ECOLOGY OF YOUNG AMERICAN ALLIGATORS by David Charies Deitz June, 1979 Chairman: Archie Carr Maior Department: Zoology 4 . The behavior and ecology of young Alligator misstsstppcensts were studied at several north and central Florida lecalities. Growth and movement rates were calculated from recaptures of tagged ailigators. Growth rates varied significantly with habitat, and were intermediace ci between rates reported for south Florida and South Carolina alligators. There were no significant differences between growth of male and female jJuvenites. Survivorship of alligators through their first post-hatching year was .30 for juveniles from lake habitats and .!7 for shallow marsh juveniles. Two-year survivorship was .14 for a sma:ii sample of lake animals. Injuries were significantly more frequent in shallow marsh than in lake juveniles, suggesting that increased predation on alligators in marsh haditats was responsible for the higher mortalities there. nest for a mean of 14 days after hatching. Most nods at this time were + 4 ? L, oe ~ a r i ~ = 1, 4-4 H q ound in the guard pools created and used oy the adult where they overwintered included stops at small pools which were apparently created by the parent. Pod dispersal began in June of the year following hatching, but after one year most juveniles were stil] within 200 m of the den. One to two-year old alligators continued to disperse, and it appeared that most two-year-olds had lost all contact with their natal areas. Rates of movement of juveniles greater than 31 cm snout-vent length also varied with locality, and were identical for males and females. Hatchling alligators emerged synchronously to bask each morning about one hour after sunrise. Emergence was accompanied by a marked increase in vocalization, and resulted in an extremely close aggregation of all pod members (social bask). After the morning bask hatchlings spent the remainder of the day in the water, largely inactive. At . Sunset, pods again began to vocalize rapidly as individuals emerged from cover and dispersed to forage. Average rates of vocalization for the first hour after sunset were significantly higher than rates observed during the day. Shortly before sunrise most individuals returned to the vicinity of their initial emergence point; final reaggregation of poags took place during the social bask. Juveniles amitted the juvenile grunt vocalization in most contexts invoiving movement by juveniles or by the parent. Grunts were used as homing signais by juveniles when separated from the pod. The high-inten- f sity grunt, or juvenile d not clearly distinct Parenta! care inyvoiving regular maternal attendance or defense was observed for 34% of a ct oO ss * < (2) “ty > G 3 is) oa a iva) im G& = o a 3 oO (bh a cr ui 2) 3 @ was defended through June. A his localities was associated with low observed frequencies of pod attendance and defense. Adult females threatened intruders with a series of threat displays also employed in other intra- and interspecific agonistic encounters. Vocalizations of juveniles were important in provoking defensive behavior by adults. Piaybacks of recorded juvenile grunts attracted adult and subadult alligators of both sexes. Aduit females responded to playbacks more rapidly and employed the inflated posture more often than adult males. Hatchlings presented to two females during playbacks were taken into the mouth and released unharmed. Juvenile ailigators in the field were initially attracted to playbacks of juvenile grunts, but sought cover losures, juveniles were if playbacks were continued. In artificial enc consistently attracted to sucn playbacks. These experiments suggested that the juvenile grunt functions te alert other juveniles and adults to novel stimuli without conveying any information on their natures. Vii CHAPTER | INTRODUCTION Few extant reptiles command the awe that has been accorded to crocodilians. Human fascination with crocodilians is long-standing; crocodilians are prominent in the mythology of many tropical cultures. As others have noted, the writings of many early New World naturalists reflect jittle reluctance to borrowing from this mythology when descria- ing crecodilian life histories. While this has made for some fascinating reading, it has left the credibility of many authors to question. Con- tradictory descriptions of the behavior and ecology of many species of crocodilians abound, and it has become common for crocodilian natural history accounts to begin with a discussion of how crocodiies do not behave (e.g., Mcllherny, 1935; Neill, 1971). Scientific evidence < o w fe) 3 o 1o) =h tr ~ ta) n 0) sufficient to reso controversies nas accumulated only within the last fifteen years. Many workers familiar with the behavior other reptiles have found early descriptions of courtship dissiey or e to accept (2.9., LeBuff, 1957). Some of this skepticism is understandable in light of the other incredible graphs and accounts of parertal care in Croecdylus “tlotteus are no cy less remarkable than Topse!! 5 discourse on tne Crocodyle of the Niius in 1608 The confusion ragarding many published accounts of crocoailian v7) @ i w | ie) Fe) re oO fd. is < mt a He G @ 5 o> ie) 5 Oo mt et 1 wn (= o lee oO a rt Gi e rad =) wm wo abe < w Ww natural history | Crocodilians are nocturnal, and even by day secretive and difficult to observe. Many species occupy densely vegetated or remote areas. In addition, they are behaviorally very sophisticated reptiles. Recent work has demons trated | that crocodilians possess well-developed sensory | abilities (Bellairs, 1971), display repertoires and social systems (Modha, 1967; Garrick and Lang, 1977; Garrick et al., 1978), learning abilities (Northcutt and Heath, 1971) and reproductive behaviors which include extensive parental care (Hunt, 1975; Pooley, 1977). Most of the generalities about crocodilians can be aeptied to the American alligator, Alligator misstsstppiensts. Neill (1971) has reviewed much of the 18th and 19th century alligator lore, and discusses the practice of applying O!d World crocodile fabies to American a Neiil decries those writers whom he believes to have been most gui! ty of jegend-mongering or an unscientific agproach. Unfortunately, Neili “ty himself falls into this category at times, and his bock inadvertently serves as an example of the phenomenon it seeks to and ‘see reviews of Neill, 1971, by Fogarty, 1972, and King, 1972). More accurate life histories (in general) of the American alligator were provided by Reese (1915) and Mcllhenny (1935). 80th of these were largely narrative and the data presented were of limited value. Renewed conservation interest in tne alligator beginning in the 1960's has led to some oreliminary quantitative studies on growth (Hines et al., 1968) feeding (Fogarty and Albury, 1967; Chabreck, 197i; Valentine et al., 1972), movements (Chabreck, 1955: Joanen and McNease, 1970, 1972a: McNease and Joanen, 1974) and ecpulation dynamics (Chabreck, 1966; Joanen and McNease, 1972b). The savere status of many alligator populations at this time has also made new information on reproductive ecology and behavior vitally important; in this area especially the speculations and anecdotes of earlier workers have been supplemented with more extensive data from recent field studies. The reproductive cycle of Alligator mtsstsstpptenste begins in March, when an increase in bellowing and courtship display by adult males and females is observed (Joanen and McNease, 1975; Garrick et fils; 1978). Increased movements by adults of both sexes, presumably related to mating activities, are also observed from March through late May (Joanen and McNease, 1970, 1972a; Goodwin, 1977). Most actual mating in the wild in Florida probably occurs in May (Garrick et al., 1978; pers. observations). Nest construction in north Florida normally begins in mid-June, possibly depending on air or water temperatures; the amount of time spent in nest construction may be somewhat longer in Florida than in Louisiana, but eggs are apparent!y laid at about the same time (Joanen, 1969; Deitz and Hines, in press). There has probably been more controversy surrounding the sub- . sequent reproductive behaviors and parental care by female Alligator misstestppienmsts than any other aspect of alligator naturai history; the confusion in the literature is certainly long-standing. William Bartram’s description of ailigator habits in 1791 includes the state- ment: ", . .certain it is, that the young are not left to shift for themselves; for | have had frequent opportunities of seeing the female alligator leading about the shores her train of young cones, Just as a nen does her brocd of cnickens; and sne is ecualiy assiduous and courageous in defending the young... . .'' (Bartram, 1791, p. 122). Unfortunately, many of Bartram's other statements about a!ligators are exaggerated or erroneous. Parental care after hatching was also referred to by Audubon in 1827 and by some of his contemporaries (see Neill, 1971). But beyond these narratives, few scientific investigations of alligators have reported any after-hatching care. Reese (1915) stated that the female alligator liberated the young from the nest in response to their vocalizations, but did not discuss their fate after this. Kellogg's (1929) review concludes that it is "generaily accepted that the adults do not show any special consideration for the young efter they are hatched,'' but also allows (with reference to Bartram) that ''such may not always be the case!’ (Kellogg, 1929, p. 13). Mcllnenny's (1935) book on alligator natural histery described parentai behaviors previously unreported for any crocodilian, or in fact any reptile. Alligator nest-guarding and nest opening behaviors were discussed, and Melthenny became the first to describe: 1) the movement ef young from the nest to the den site, led by the female; 2) the persistance of the aggregation of young alligators, hereafter referred to as a pod, into the following spring; 3) defense of the pod by the female through the following spring; 4) growth and food habits of young aliigators; and 5) the eventual dispersal and maturation of juveniies. As Carr (1976) sointed cut, most of McIlhenny's observations were ubsequently proven accurate. His account was, jike its predecessors, wr primarily narrative, and until! recently there were few quantitative data available on alligator benavior. Chabreck (1965) provided additional reports of the movement of young alligators from nest to den, and followed Mclihenry in implying that there was a limited amount of protection by the parent. Both Chabreck (1965) and McIIThenny (1935) worked with Louisiana coastal marsh alligators, and indicated that in this habitat pod dispersal began in spring. Fogarty (1974) reported that young alligators in the Florida Everglades may remain near the female's den for two or three years after hatching, but denied the existence of any active protection by the parent. Several! large scale studies of alligater nesting ecoloay, covering most of the animal's present range, were recently completed; all of these reported a variable degree of nest attendance by the female and in most instances opening of the nest by her in order to liserate the young (Joanen, 1969; Fogarty, 1974; Metzen, 1977; Deitz and Hines, in press). Of all the accounts since Mc! Ihenny only one, based on a single cbservation, provided any further direct evidence for parental care of the young after hatching (Kushlan, 1973). At the inception of this study most other aspects of juvenile alligator behavior and ecology remained equally obscure. Despite the wide variety of wetlands habitats occupied by alligators, information on growth and movements was availabie only for the Louisiana coasta! marshes and, to some extent, for the Everglades; no data were avail- able on tne influence of habitat on life history parameters. dObser- vations suggesting that the vocalizations of young alligators were the princiole mechanism by which pod cohesion was maintained were made by Campbe!! (1973) and Herzog (1974), but no exseriments had been performed to test this hypothesis. The variety of habitats occupied by Alitgator misstsstpptensts in north and central Florida provided an opportunity to examine juvenile behavior in different ecological contexts. 1 began this investigation to: 1) obtain information on the growth, mortality, move- ments and dispersal of juvenile alligators in Florida; 2) determine the extent and persistence of parental care; 3) examine communication and social behavior within the pod through field observations and experi- ments; and 4) determine the influence of habitat on the above by studying juveniles in different locales. Several excellent accounts of social behavior and parental care in other species of crocodilians appeared during the study (e.g., Garrick and Lang, 1977; Pooley, 1977). Conse- quently, it also became possible to make some preliminary comparisons a between Alligator mtsstsstpptensts and other crocodilians with respect g to the ecological and evolutionary significance of parenta! care and juvenile social groups. CHAPTER 1! STUDY AREAS Orange and Lochloosa Lakes Orange and Lochloosa Lakes (Alachua County) form a twin-!ake system connected by Cross Creek, which runs from southwest Lochlioosa Lake to northeast Orange Lake (Fig. 2-1). Both are large mesotrophic takes, with extensive marshy areas covering portions of the basin (Brezonik and Shannon, 1971; Table 2-1). Most observations of juveniles were in these marshy areas, although several groups of juveniles were located along the marshy fringe around the open water portions of the lakes. Characteristic of marsh areas of these lakes is a heavy build- up of peat. Gasses formed by decomposition bring large chunks of peat to the surface, resulting in floating islands and floating mats extend- ing out from the lake shore. Vegetationai composition of these islands * * and fringe areas is largely Sagtttarta lanctfoita, Cladiwn jaratecen, 4 H Ny v3) vv Pee ga, 7 mht Tv nee baat ’ |< OORT: Ie Se AYAPOCOTH LZ WMD 2 ip HATA y Pantun SP. Myrred Cert; erd, CEpracancvnus oectdentalts and DJecodon vertictilatus. Mupnar lutem covers extensive portions of the open water margins, with Ztenornta crasstpes, Linnobtum spong7a and Pretia strattotes cammon in more sheltered areas. There is abundant submerged growth of Sydrtlla verticillara. Seascnal variation in water temperature at Orange Lake is shown in Fig. 2-2. Predictably, shaliow water areas in the lake fringe and marsh regions shewed srearer diel fluctuation, heating up rapiaiy in “i Table 2-1. Study areas. Mean Surface 2 ; 1 Location Depth (m) Area (ha) Trophic State Index 1. Orange Lake 1.8 5330 4.3 - Mesotrophic 2. Lochloosa Lake 2.9 5.2 - Mesotrochic 3. Lake Griffin 2.4 4310 13.7 - Hypereutrophic 4. Station Pond € 7 242 (3.6 - Mesotrophic) 5. Payne's Prairie 0.4 - 0.9 5036 --- 6. Lake Wauberg 3.8 10] 7.4 - Eutrophic 7. Biven's Arm 1.5 58 14.7 - Hypereutrophic 8. Carr property > | ca 5 --- a 1 7 e . . - Values for mean depth and trophic state index are from Br Shannon (1971) except values from Payne's Prairie which a White (1974). De — yes 4 ; Surface areas taken from U.S. Geclogical Survey data, or calculated from aerial photographs via planimetry. Figure 2-1. ALACHUA COUNTY LEVY Locations o Florida. MARION COUNTY 10 km po ae eae ee eee LL LAKE COUNTY principal study ares in north and central Numbers correspond to Table 2-i. Dashed portions of areas 1 and 2 indicate the marsh areas of Orange and Lochloosa Lakes. 10 ‘araresdg s,auded pue uljst1sa9 aye] faye] obuesg Jo Saunqeasduay s9j7eM ul sabueys peuosesg *7~-¢ asnd14 HLNOW . 226! | 9161 | G26] plo! ON,0,5 WOE AWS PI ONOS EO ON 0.8 VCE FON OSV EWN fo AINE uv, we av] “e_ NiSAINS JONVYO HW a R 2 (iia ca) (Sami i” mia Sarat ca a aor ro) Ol re] m) (Oc) SHNLVHSGWAL 07H the sun and cooling below average lake temperature at night. Water levels fell gradually throughout the study deriod until 1977, when abnormally low rainfall resulted in a 20-year low in the lake level (Fig. 2-3b). This produced exposed mudbanks around lake shores and an extension of the fringe vegetation into the center of the lake. The Orange Lake alligator population at the height of the drought was estimated at over 2500 individuals based on night census data (Hines, unpub. data). Payne's Prairie Payne's Prairie (Alachua County) is a large solution orairie typical of Florida wet prairie habitat, except that drainage canals and levees have been constructed throughout for flood control. it is now & pertion of Payne's Prairie State Preserve. White (1974) has presented data on hydrology, vegetation and dynamics of piant succession on Payne's Prairie. Alligators are commonly fourd only in the wetter portions of the basin. DOeminant plant species in these areas include Pontederia cordata, Jusstaca veruvtiana, Typha so., Salix carolinensis, Panctum hematomon, Juncus 2ffusus, Nelunbo lutea and Hydreectyle unbellata (White, 1974). Water levels during the study period are presented in Fig oO (@] Zs | TF 4 2) om a (ea) a | oO ia 3 mM. i iSe) a | Oo = ie) et i] + a (Dd 4 ne) @ a! vw ct | 35 me} Q ia Ww i is) = a w —< “th c ie) ct c tv ct ° oJ wh Aeriai nest surveys in 1975-1977 and casual cbservations at night ' tir ted by Dy t a Prai;yi i pat Sj. ewitote? c _ alli - jpulati indicated that Payne's Prairie probadiy supports an a!ligator population compéradle to Orange Lake in density, but no censuses were conducted. WATER LEVEL (M ABOVE MSL.) NON nb = o am o @ Ee i a a a a, a ee id — » Basics, WATER LEVEL (M ABOVEMSL.) N fa) » S mm fh PAYNES PRAIRIE “7 \ GAUGE | oo 16.4 \ | 16.2 \ J \ | 16.0 \ | \/ 158 ? 15.6 Toate Tio) cto FMAM J'J AS ON'DIJ F MAM J JAS o'ND|y'F MAMJJA sono 1975 1976 i977 18.0 1 78) a I7.6 \ eS | ” Perr yf I7.4 4 \\ \ a i 17.2 cae ” SUA i. *~ N \ a ; oe \ I7.0-4 ‘eS, / A | SS / \ Vw \ i6.8 ORANGE LAKE ----- \ 66-1 LAKE GRIFFIN ——— *. 16.44 i ‘ i { H tt Go § JF wa wl uulalslo'n'p [ule WaMu" ASOND i975 1976 Figure 2-3. Water levels at three study sites, 1975-1977: Payne's Prairie, top; Orange Laxe and Lake Griffin, sottom. 13 Lake Griffin Lake Griffin (Lake County) is the last lake in the Oklawaha Basin chain of lakes; it drains directly into the Oklawaha River. All observations in this study were conducted in Picciola Cove, in the south- western portion of the lake. As in Orange Lake, peat build-up has produced a floating mat around the fringe of the lake; in Lake Griffin this forms a dense thicket rather than a floating marsh, composed o ee eed v principally of woody plants such as Acer rubrum, Cephalantaus oecidenta Salix carolinensis, and Nyssa sylvatica. There are emergent growths of Sagtttarta sp., Nuphar lutem and Pantcwn repens. Alligators of a}l sizes used trails and holes in this fringe. Lake Griffin was characterized by Brezonik and Shannon (1971) as hypereutrophic (Table 2-1), The development of this condition was due in part to high volumes of citrus cannery and municipal sewage effluent, and also to artificial stabilization of water levels. Water level Fluctuations were minimai during the study (Fig. 2-3b). Water tempera- tures (Fig. 2-2) averaged higher than in Orange Lake, probably as a result of its more southerly location and greater depth (Fig. 2-1; > itigator reproduction on Lake Griffin has been explosive in recent years. This has produced populations which are extremely dense and composed largely of juveniles less than 150 cm in total length (Hines unpub, data; pers. observations). C Station Pond Station Pond (Levy County) is the only study area located in the Gulf Coast drainage (Fig. 2-1); it forms part of the headwaters of the Waccasassa River. It is a shallow, sand-bottomed basin, surrounded mostly by pine flatwoods except at the Southwestern end where it grades into cypress swamp. Principal emergent plant species in the marsh were Panitcun hematomon, Numphaea odorata, Brasenta schrebert, and Pontederta cordata. Slightly higher islands in the marsh, referred to as "heads, were often associated with alligator holes. Vegetation on these heads was precominantly Pantewn hematomon, Cephalanthus occidentalis, Sagtttarea lanetfolta, and a variety of undetermined species of ferns and herbs; some heads also included one or two cypress trees, Taxodiwun dtsttchun. No monthly water level or temperature data are available for Station Pond; temperature data available for Payne's Prairie (Fig. 2-2) are probably a reasonabie approximation. The water level of Station Pond appears dependent on regular rainfall, for during periods of low rainfall it would drop markedly. Station Pond became comeletely dry in May 1977, and except for a brief reflcooding after rains in September, remained dry until January 1978. During this drought, the only surface water available was in alligator holes--depressions which are deepened and kept clear of emergent vegetation by the activity of the resident alligator (see MclThenny, 1935,and Craighead, 1968). Prior to 1977 the alligatsr population on Station Pond was estimated at §C-120 individuals (Hines, Woodward and Deitz, unpuo. data _ An Brezonik and Shannon (1971) have presented productivity and water chemistry data for Watermelon Pond, a marsh which is slightly deeper but otherwise very similar in appearance to Station Pond. Watermelon Pond is also in the Waccasassa drainage and is located 2.2 km to the northeast of Station Pond. The trophic state index for Watermelon Pond has been used for Station Pond (Table 2-1). Occasional data were also obtained on alligators in three other locations, all in Alachua County: Biven's Arm and Lake Wauberg, both part of the Payne's Prairie drainage system, and a smali pond on the property of A. F. Carr, Jr., near Micanopy, Florida (Fig. 2-1). Significant features of these study areas are discussed with results as appropriate. CHAPTER II} GROWTH, MORTALITY AND MOVEMENTS OF JUVENILE ALLIGATORS Introduction Quantitative ecological studies of cracadilians have been few, and with the exception of Cott's (1961) work with Crocodylus niloticus have Pp Y been restricted to populations occupying single habitat types. Most data on growth and mortality in Alligator nisstsstpptensts hav uv (wD is) o ss o from the Louisiana coastal marshes, where salinity is the only major environmental variable affecting populations in different marsh areas (Joanen and McNease, 19726; Chabreck, 1965, 1971). Growth rates of Louisiana and south Florida juvenile alligators are comparable (Mc!ihenny, 1935; Hines et al., 1968) and are both much higher than rates reporte for South Carolina (Bara, 1972; Murphy, 1976), suggesting that length of the active season is important. Data on natural mortality of A. mtestsstpptensts (or of most other species) are non-existent, except for indirect conclusions based on life tables (Nichols 2¢ al., 1976} Chabreck (1965) described the post-hatching movements of A. misstsstpotenets in Louisiana, and indicated that they were influenced by water levels. Similar results were reported from the Everglades (Fogarty, 1974), and formation of pods was apparently typical after on of these pods, distance moved and extent of interaction with the parent were not clearly defined. WNeiil's = uveniles did not form groups were | entirely unfounded, but the extent to which lake habitats in north foxy 7 and central Florida might cause divergence from marsh movement patterns was unknown. The implications of Chabreck (1965) and Fogarty (1974) that pod formation, dispersal and possibly duration of parental care were affected by water levels and other habitat characteristics indicated that information on the natural history of Florida juvenile alligators was basic to any understanding of the significance of social behavior and parental care. Methods Aliigator nests were located on Orange and Lochloosa Lakes and Station Pond using aircraft, and on Payne's Prairie by searching levees on foot. Brushy cover in the fringe areas of Lake Griffin made both air and ground searches for nests there impractical, and only two were located. Nests were usually checked semi-weekly and observations on female benavior were made at this time. Observations of one nesting Temale were also made at the Carr property. After hatching, pods were Followed on foct or by canoe on Payne's Prairie and at Carr's, and by peat on Orange Lake and Lake Griffin. Most alligators were captured at niaght--those under 155 cm in total length by hand or with tongs. Snout~-vent iength (SVL. taken from the tip of the snout to the posterior angle cf the vent), total length (TL), and weight were normally recorded for all alligators captured. Evidence of injuries was also recorded. Loss of the tail tip, ¢.e., was considered tc be a minimal disfigurement; scars or wounds on the head or trunk were considered to be severe injuries. Sex was determined by cloacal examination for specimens with a TL of 45 cm or greater (Chabreck, 1963). Locations of all captures and recaptures were plotted to the nearest 100 m using aerial photographs; even more precise locations were usually possible with this method. Alligators were marked with monel tags (National Band and Tag Co., Newport, Ky.) inserted through the webbing between the second and third toes of the right hind foot and released. when working with pods of hatchlings, an effort was made to capture all individuals sighted. 1! assumed that this resulted in a relatively equal capture effort for successive captures and used the Lincoln Index to estimate the number of hatchlings in a pod. Alligators of all ages became extremely wary when recapture attempts were frequent; therefore, the interval between successive captures of the same pod was usually 3 months. Since pods were usually well separated, locations of different pods could be determined without confusion by visual sightings. Survivorship was calculated by two methods: 1) hatchlings tagged at the initial encounter witn a pod were taken as a representative juent recaptures cf these initially tagged individuais n wo 3 i | 0) “ m =| tL “uw c om wn wo QO oniy were usec to determine survivorship; 2) estimates of the number of hatchiings present on a given date were made on the basis of either tne Lincoln Index or visua! census, whichever was greater. Tne movements of 5 aljligaters on Orange Lake and Payne's Prairie emetry. Transmitrers of 150-151 MHz with short gurations of the whip antennae were used. Battery sizes and cont packages varied, but none of the packages exceeded 5% of the body weight 3 of the alligator instrumented. Two attachment methods were used: 1) steel wires molded into a water-proof instrument package were passed through holes drilled transversely through the nuchal scutes of the alligator; or, 2) straps of nylon elastic and surgica! tubing were passed around the body anterior and posterior to the forelimbs. Longitudinal strips dorsal to the forelimbs prevented the transmitter from sliding ventrally. !nstrumented alligators were located at least once every 72 hours. Data Analysis All analyses of growth and movement data were done by computer using standard SAS76& statistical packages (Barr et aZ., 1976). Growth rates were expressed as increment in snout-vent length (SVL) in em per month or im weight in gm per month, calculated by the following formuia: SVL2 (or Weight 2) SVLI_ (or Weight uy Days from capture | to capture 2 Movement rates were calculated in a similar fashion by substituting distance moved between captures for growth increment. In order to examine the effects of increasing bedy size on growth rate, alligators were divided into 3 size classes: class |, < 20 cm SVL; class li, 21-31 cm SVL and class II!, > 31 cm SVL. The rationale for juveniles from about 0.5 to 1.5 years old (yearlings, SVL class 1!) and larger juveniies (SVL class t!1), 1.5 years old or older which had begun g J : J significant dispersals {see below). Some variation 20 produced by size was also reduced by expressing growth rates as percent change in initial SVL (or weight) per month. Observations of winter dormancy in north Florida alligators indicated that little growth probably occurred during this period; Food consumption was much lower than during other periods (Deitz and Hines, unpublished data). Recapture intervals of juvenile aliigators from different locales varied considerably, and included different proportions of winter days. For example, an alligator captured on | May and recaptured on | October of the same year had the same recapture interval (5 months) as an animal captured on | November and recaptured on | April of the next year. Growth increments of these two alligators were likely to be quite different. In order to eliminate this variable when comparing growth rates between locales, the days from ! April through 31 October were considered to be ''growth days,'' while days from | November through 31 March (151 days) were considered to be "no-growth days'' and were not counted in the recapture interval. Monthly rates calculated in this manner and then multiplied by 7 compared favorably with annual growth rates calculated for long-term recaptures. Results Growth Growth rates of juvenile Alligator misstsstpptensts from different localities varied considerably (Table 3-1}. As expected, the rates decreased at ali locales as sody size increased. At all sizes, alli From Orange Lake grew faster in length and in weight than animals from 2] to° > d fuol1qeIS < abuesg LO° > d oes Ud SBhasqnem < obueig so° >d lo" > d furggtay ‘uljglsy < uolqzers ‘obueig TV < vorqzeqys £7 abueay WLb a 4702 H°SZ + LIS Poteet gO + L°0 Ol Baaqnem 4 igi + £°22 €"gt + 9°95 6°€ + 9°9 6°O0 + 9° 9 Pd YOIIRRS 1 C9 + 6°S 1°02 + 1°02 S°t + £9 6°0 + 9°0 A UlASIAD 6°O£ + 2°E7Z 6°€OL + 4°19 L° + 9°9 aut £71 89 1] abuesg so’ > d SO’ > d fursytay “tg S,auAeg < Pd UO!1Ie7S 1 < Pd vorqzeis £7 abueug pue uljji4y 7 £7 @bueig 9°S + £°6 gO + E'l g Baaqnem 4 _ _ Lee + dey S'o0+ L°0 l 41g S,audeg S°El + O°eH Chl + 9°44 1°S + 6°6 Oise £71 gl Pd YOL}EIS | Q°HeE + O°ZE S°ye + "EZ e°6 + 2°11 7 ls <1 98 Ulgst4 7 6°67 + O°7H 6°62 + S'EE £*h + 0°7t = L9°0 + O8't O61 7 ebueig “ow/abuey) x yj uop /w6 ‘ow/abuey) x Y1UOW /UD ~ sa.injdesay 9p R007 SSP] OZIS 1yHi9mM ul aseod4souy| TAS Ul eseaaouy "SayePoO] eplso1y Je4zuad pue YyAsOU JUussassIpP WOAS SsOQeBIELe apluaanf yo saqze4s yWMouy “|-E€ ayaey 22 other sites, while growth of alligators in Lake Griffin was generally less when compared to all other locales. Growth rates for Station Pond and Orange Lake were comparable except for size class I!!1; Station Pond data were based on captures of more large juveniles (SVL 50-70 cm) than any other areas, which probably biased these rates downward. Growth rates at Lake Wauberg were generally low, although samples were too small for valid comparisons. Differences in water temperatures (Fig. 2-2) and water depth (Table 2-1) which might affect the length cf the active season and/or food abundance, did not satisfactoriiy explain differences in growth rates. Stomach contents of juveniles from Orange Lake and Lake Griffin suggested that in Lake Griffin low availability of aquatic invertebrate prey was limiting to alligator growth (Deitz and Hines, unpublished data). Data from two 1975 cohorts which were regularly recaptured on Orange Lake (Fig. 3-1) and Lake Griffin (Fig. 3-2) show the actua! growth of juveniles for two years after hatching. These and other data from long-term individual recaptures compared favorabiy with the mean rates calculated from all recaptures within a locale (Table 3-1). Recaptures from October through April supported the assumption that there was no growth in north Florida juvenile alligators during a winter dormancy period of roughly five months, from 1 November to 31 March. This can also be seen in Figs. 3-1 and 3-2. There were no differences in growth rates between maie and female juveniles when tested either within locales or with pooled data from several locaies (p > .05, t-tests); thus, data combined in preparing Tabie 3-1. The sex ratio "UO!JEIAVP psepueys + ued yUasSaides sueg “LL61-SZ6L Sssoqyeby ype Burpyszey ayeq eHuewg yo yamouyg +1 -¢ aanbl4 2h LHOISM 907 (w6) 20! 4 pO! 226i 9261 ¢/6! gon os Vr FWA YW sd FTO N CS re re dk df a ne an nel Ad il Pi wh a ae G a ‘ ii er rs o— o 4. Pid f T | 2 ~ ¢ f° 7 re $---4+' a J L f ra / +7 a Ly 4-7 ] ee ae T | e— = | | | i: + aA (Hoiam po L- ee , AS @- een — oO! OF - SE -Ov INSA - LAONS rr | Hi (wi) “uOl eiAap psepueys + ueou yuaseides sueg *//61-S/6I ‘ssozebi ype Burpyosqey ulssgiayg oyeT Jo youn *7z-E a|anbr4 ZO We a,N_0 wr 9161 G/6I Svc CW VW A Ppa No Weak Wl Yanan Oa Wah ROA IRS ees Te) (Mbt Tee Pane oO} ‘ dyes ie — H i if ? ae J — a Z yt ie / | al | / | 02 | } ia) | Se ae or d, | LYOHOO PL6L IOI om ut 1UOHOD bL6E VAS GeO LUOHOD GLE) LHOIAM 4----4 LYONOD GG TAS @e— @ OF alligators was 1.45:1 (males:females); for 443 SVL ciass 11! alligators it was 1.68:1. These ratios were not significantly different (p > .05, Chi-square test) and the sex ratio for al] juveniles combined was 1.59:1, or 61.3% males and 38.7% females (Teble 3-2). Survivorship . . . 1 The survivorship of A. mississtppiensis frem hatching through the end of the first year proved to be surprisingly high for some pods; both methods of calculation provided similar results (Table 3-3). Roughly half of all hatchlings from Lake Griffin and Orange Lake survived the winter, and survivorship after one year averaged approxi- mately .30 (Table 3-3). Mortality for 3 pods in shallow marsh habitats (Station Pond and Right Arm Marsh, Lochloosa Lake) was greater, although differences between lake and marsh survivorship were not statistically significant. Due to the increased dispersal of two-year old animais and, in some cases their learned avoidance of capture techniques, few data were obtained on survivorship from the first through second yeér. On Orange Lake, survivorship of two pods from 1975-1977 was at least .14 (10/74) based on estimates, or .19 (6/3!) based on animals tagged and recovered. On Station Pond 4 (.10) of an estimated 41 animals from two pods were alive after 2 years. Predation on hatchling alligators was never observed. The wide range of survivorshios of different pods suggested that some groups were less suscentible than others, but there were no clear differences n microenvironment, behavior of natchlings or female attendance (see 28 Of: 19 1426S eh: ls Lys Z£ 289 €S:Lh 18d ce 8 7¢ 6S he ont 94 HZ Le 9z1 of ,eIOL 49410 Hbusqnem 4 Iq S,auAed Pd uo1yeqs UlfJstag J "SBLedO,[ epl4sol4 je4}us. pue YyysoU JUus4a4y4IpP Wosy S4ozeHi tye ayrueanf yo sor es Kas LE:¢9 A%W% Hl sa, ews, €6l So, eW jebuergt—CS~S “T-€ FLqeL 29 = - (Zi/Z) zt* l - - (Li/L) th? { PSOO[YD07 . (hE/n) ZU" (tH/B) Oz z (hE/L) 1Z* (UH/EL) ET uojieyg 9461 ero (Aiuo S/6L - O£°) (161/85) O€° 9 (SZ/LE) Lh: (BEZ/ELL) By g MISSHD 1 ere (9t1/0H) SE" (017/85) gz" L (Lyl/9L) 75° (SLE/LSL) 05° Ut abies * ON (1E/Ol) 2° (SOI/EH) LH" Y abuesg LL6I SYeq = = (78/92) Le" rA (SH/8l) OF (QLI/IS) €4° £ UIs dd4AD L6 (S8/nZ) Bz° (9EL/SE) 92° S (Sg/Zh) 6° (9E1/L9) Gh’ abueig «PAO | (42/8) O€° (601/EE) O€° y (€€/61) BS° (OZL/Z9) 25° S ULjpd4D GI (1E/9L) 25° (hL/EZ) LEZ (1e/nz) BL" (HL/Ln) 49° abuesg «4 | sbe) wos4 pa yew!ysq SPOd she, wor poqewiasy = Spog.— apes0y.—~—SBOQ—sdVETIGMY # # Aea, | - Buryorey syjyuow 9 - Suryoqzey sapeoo, Aq ‘sea ysaty ay. YyBnosyy ssoyebBsi ype Bul ;yoqey yo diyussoatasng *€-€ apqey 30 the range on Lake Griffin was .14 to .56. Temporal patterns of attrition likewise gave no clues to predator identities. Al! pods showed a reduction in mortality with age, which could be due to increased body size, learning, or both. However, [Initial mortality was much higher for some pods than for others at the same site. For pods in all habitats attrition during the winter was also less than that observed during the active season. At least 67 of an estimated 88 hatchlings from 5 pods alive in October were alive the next March; this was equivalent to an annual survivorship of .43. Indirect estimates of mortality from other locales suggested that survivorship of individual pods was quite variable there also. One pod of at least 14 hatchlings had vanished from Lake Wauberg by the following spring, but night counts of 5 other pods in 1977 indicated that | year survivorship on Lake Wauberg was probably as high as that on Lake Griffin. Survivorship of two pods from different years at the Carr property were less than .10 and probably 90. Injuries. The most common injury to small 4. MLSStsstppiensts was loss of the tail tip (Fig. 3-3). Tail tip losses had cecurred in 9.14 of my entire sample (n = 1685) and accounted for 58% of all injuries. Loss of more than 20% of the tail was recorded in 29 alligators (1.7%), loss of a limb in 2! (1.3%) and severe scarring on head or trunk in 7 (0.4%). The overall injury frequency increased with size of the alligator (Fig. 3-2). There were supstantiai differences in the percentage of injuries between localities. Juvenile alligators (SVL < 7G em) from sha! low marsh habitats (Station Pond and Payne's Prairie; n = 389) had an PERCENT INJURED 25 = TAIL TIP MISSING 20 (/] SEVERELY INJURED LAKE MARSH LAKE MARSH LAKE MARSH! SVLII - 20CM SVL 2)-31CM SVL > 31CM Figure 3-3. Frequency of injuries in aliigators from lake and marsh habitats in north and central Fliorida. 31 32 injury frequency of 15.4%; this was significantly higher (p < .O1, Chi-square test) than the 6.7% injury frequency for al! lake habitats (Orange Lake, Lake Griffin and Lake Wauberg; n = 1096). Injuries to marsh alligators were also significantly more likely to be severe than those of lake animals, and the frequency of these severe injuries increased with size more rapidly in marsh alligators than in lake alligators. Growth rates (SVL and weight increments) and movements (see below) of alligators missing only their tail tips were not significantly different from uninjured alligators (p > .05, t-tests within all locales). Growth rates for a sample of 1] severely disfigured alligators (SVL > 31 cm) from Station Pond were not significantly different from growth rates of normal alligators. Movements and Dispersal The movements of 17 pods in marsh habitat (Payne's Prairie, Station Pond and parts of Orange and Lochloosa Lakes) and 6 pods in lake fringe habitat (Lakes Griffin, Wauberg and Orange) were foliowed for at least two weeks and usually longer after hatching. Observations were also made on movements of 7 additional marsh and 15 additicnal lake fringe for which the nest locations were unknown. The initial location of a pod after hatching was usually a pool or wallow near the nest, referred to as @ ''guard pool" by Mcllhenny (1935). Females which defended their nests were almost invariably present in these guard pools during incubation (Deitz and Hines, in press), but guard pools were also present at nests which were not reguiarly attended. On Payne's Prairie 33 and Orange Lake, 65 of 93 nests (70%) had guard pools located within 3 m of the base of the nest. Most other nests had guard pools within 10 m of the base, connected to the nest site by well-defined traiis. Both the presence of freshly smashed vegetation and the increased depth of these pools when compared to the surrounding marsh suggested that guard pools were actively created by the nesting female. Some pools also appeared to have been enlarged by the female just prior to or shortly after her nest hatched. All alligator nests examined on Orange and Lochioosa Lakes and on Payne's Prairie had a characteristic semicircular excavation after hatch- ing, and it was concluded that all had been opened by the female (Deitz and Hines, in press). Hatchlings were probably led or carried to the guard pool by the female during hatching (Kushlan, 1973; Meyer, 1977) although hatching was never observed. Hatchlings emerging late and/or without the assistance of the parent probably had little difficulty finding the pool because of its proximity, ard could also use the vocalizations of other hatchlings as an aid {see Chapter 5). On one occasion, two hatchiings with umbilices still attached were found halfway down the trail leading from the nest to the guard pool 5 m away. The remainder of the pod was in the pool, vocalizing regularly. The presence and distribution of nest guarding pools, wallows and other sites associated with adult alligator activity were important in determining the movements of pods after hatching. If a guard pool was present, hatchlings in 2!) habitets typically remained in the vicinity of the nest for several! days. For 9 such nests, hatchlings spent a minimum of 14.3 + 10.5 days (range 6-39 days) within 10 m of the nest. as a Two other nests that were closely observed had no guard pools nearby, although some water was present at the base of the nest. Hatchlings from these nests spent, respectively, maxima of 5 and 7 days near the nest before moving away. Three additional marsh nests were located adjacent to large pools which appeared to be the female's alligator hole or den site; these pods showed no movement from hatching through the following spring. After this variable period near the nest, pods began moving away to their overwintering site. The integrity of the pod was maintained throughout these movements, which occurred as regularly-spaced journeys separated by periods during which pods remained in the same pool or series of pools (Figs. 3-4 and 3-5). Displacementsof up to 40 m in 24 hrs were recorded; after a long shift in position the pod usually remained stationary for several days. Females were observed moving with their pods in two instances, once during the day and once at night. Parental presence during most other movements was inferred from the fresh trails that connected new locations with the previous ones. Many of the smali pocls in which pods were found at this time were clearly created or eniarged by the movements of the female. Stands of Panicwn hematomon, Pontederta cordata, Sagittarta laneifolta and other soft marsh plants were found smashed down in roughly circular patterns 3 to 5 m across, which created enclosed pockets in the marsh or lake shore. The dens of three females which nested on Station Pond in 1975-1577 were adjacent to heads or peat isiands in the marsh. Traiis and pools wound through all of these heads like shallow canyons; hatcntings from two successful nests used these pools for the first two months after “alareadg s,eudeg ‘pod tyg/ ayy jo srusweacoy “H-£ aanbis Ln isa) AJSAR7 G1, dasz-Bnvog payyou @ LS3N = ‘eg ssictaeealiaiacaeiasacictas sui oe - eee ga ser G88 cime { ii Ss caateat ie Ac i Ee aa ose nae tien et teed, de geek ct / Pa ~— we, ee ee) G2,das 9] Gi,das gir } = i / / / U ' ! / / - cteecciaeens ; (ussow) ~ WO] / “A = WOb er) / 92, aunt GC] = 7 j ee ~N ¥ / Z \ { voljopaban 7 at Pie, ae paysows / pee Na | pint Pa i , 4 et ‘ XW a 91, how G -¢ at Q2 aUND HZ * wees al / DW YVOW OF e "y = awe / aa ah ia F GLZPO6 / == _ ju? ! anes. \ I = SoS A , / sdasaz yee Nee JIMIWed =S,INAVd Nn - “oe ‘pod ase) 4/6) 242 JO SqUusUaAOW °G-E J4nb14 tea ae reas "suv “4095 tI costiag e : ee S490 $2-E2- {49,0M) ga i, dag ¢ “3 38 hatching and intermittently thereafter. Observations of young alligators using heads with similar networks of pools were made at other shallow marshes near Station Pond. Two heads with adjacent poo!s were known to be used by large males. Neither of these had the extensive network of small pools observed in heads with young; the large pools adjacent to the heads were wider, and the a!ligator trails present seemed to be straighter. These casual observations suggested that long-term occupancy of a den by a reproductive female alligator might result in permanent habitat modifications related to care of pods. Most pods reached the den or overwintering site by mid-November. This site appeared to be used extensively by the adult female if it was not actually her den. Total minimum distances moved for 9 marsh pods which were tracked from nest to den averaged 80 + 34 m (range 25-120 m). The exact route taken was probably more circuitous, as illustrated by the movements of a pod through shallow marsh at the Carr property in 1974 (Fig. 3-5). Though the actual distance from nest to den site was 116 m, the minimum path length for the pod was 445 m, and included two reversals cf direction and four stops at different sites before the wintering pool was reached. Pods on Lake Griffin and on the fringe of Orange Lake showed a slightly different movement pattern. After leaving nests on the fringe of Orange Lake, pods moved gradually out to the edge of open water, and remained there until the onset of coid weather in November; at this point they moved back to a den site in the fringe (Fig. 3-6). Only tro nests were located on Lake Griffin, pout both of thepods from these nests followed a pattern similar to those on the fringe of Orange Lake, Each year in mid- to late September many pods became visible on the fringe ee) LD Ke | ORANGE LAKE | 6-i5 Oct '76 Small poo! | 30 Aug- |4 Sep'76 ADULT 10 Nov 76 i g ) | Pod not located Vio se \Q a @ «NEST HATCHED é 24-30 Aug '76 Figure 3-6. Movements of the 7609 pod, Orange Lake. of Lake Griffin. If peak hatching 's assumed to be at about the same time as on Orange Lake (late August to early September), these pods also must have spent approximately two weeks near the nest before moving away and did not follow a direct route from nest to den. Hatchlings moved little throughout the winter and, as already noted by Chabreck (1965), were largely inactive except on warm, sunny days. There was some tendency for pods to be extremely closely aggregated during cold weather, and their location in extremely smal! pockets or pools made them difficuit to detect. Two pods observed on Lake Griffin during the winter of 1976-77 were located several meters bac < from the cpen water margins of the brushy fringe. Both occupied pools tess than 150 cm in diameter. One pod observed on Orange Lake in March 1977 occupied a pool approximately 2 m across. Water tempera- tures throughout the winter on both Lake Griffin and Orange Lake ranged from 15-20°C (Fig. 2-2). Hatchlings were siuggish at these temperatures, but were capable of coordinated movements and vocalized readi!y when captured. When disturbed, they dove underneath the floating mats or vegetation into underwater refuges, some of which appeared to be caves used by adult alligators. Some basking took place on Orange Lake during the winter, and hatchlings on Orange and Griffin also fed, although at reduced rates, as indicated by stomach contents (Deitz and Hines, unpublished data). Pods not followed closely during the winter were found in March and April where last seen the previous fal}. Dispersal of alligators following their first winter was documented by periodic recaptures of pods on Orange Lake, Lake Griffin, and Station Pond, with supplementary observations of marked and unmarked juveniles 4] from these and other locales. The mark-recapture phase of the study, conducted from 1974-77 in conjunction with the Florida Game and Fresh Water Fish Commission, resulted in 559 recaptures of 382 alligators, from a total of 1685 alligators tagged; the majority of these were less than 150 cm in total length. Representative dispersal patterns of pods of alligators marked on Orange Lake were plotted in Figs. 3-7, 3-8 and 3-9. All three pods demonstrated a one-dimensional spreading along the lake or marsh fringe; dispersal distance after one year was similar for 7 additional pods studied on Orange Lake. Figures 3-7 and 3-8 also illustrate that the center of dispersal was the overwintering site rather than the nest. Seven pods followed on Lake Griffin (Fig. 3-10) showed the same sattern of bi- directional, linear spreading also observed on Orange Lake. However, one-year dispersals on Griffin appeared to be slightly less than on Orange Lake; this was possibly related to slower growth of Lake Griffin juveniles. As expected, dispersal on Station Pond and in marsh areas of Orange Lake was more two-dimensional, but the time sequence of progressively greater displacement from the den site during the first summer was similar. Pods were still recognizable as discrete aggregations in June of the first year after hatching in both lake fringe and marsh areas of Orange Lake, but they began to jose cohesiveness at about this time. : i Reaggregation into a single group following a night's feeding (see Chaoter 4) no lonaer ceccurred. and several ciumps of siblings scattered g g along 100-300 m of shereiine cr in aifferent pools in the marsh were 42 a > *y 5% . Seen . w/other pod 2172 POD hatch Sept'75 72 recaptures ORANGE LAKE : tee 35 = ayn ~ yo 3 ye shy? ee a ess Si oS eee a Figure 3-8. Dispersal of the 2301 ped on Orange Lake, 1976-1977. Sed r Mg GA 52 Ge a he. 9\ - eee CSS +oge NEST s en Aug i975 « 4 ES. he tgie gas ORS K See iP 2 Nov 77 ——— se 17,28 Sep'76 —W" \6, 30 Mar'77 : t ORANGE LAKE 20 June '77 7 ae ag ry q “ Sc pee eae £ vee Fa ae 5 : fe Raed al MeL tne: 45 vate te dys, a NEST- ft ive) i= gl we = oh 6S 8F ta © 1a ' ar val WwW) ad ee a ee \ te \ 13 Aug’ ic 6-197 7 pod on Orange Lake, i 06 he 76 % igure 3-9. F Bis Raa rE Bigs Pale Moraes ? Cue) Initial ioetticn 2539 pod Sept 77 One capture from 75 LGI pod ——a. ¥ PIGCIOLA GOVE ial es LAKE GRIFFIN way ees ene eee! ee “Initial location “Tnitio! location yas ft SWAMP: Sa GEG % -75.LG Lek ent es ciniti ee lceonorS One year dispersal md 75 LGS pod Ta Sep 76 Teo « if 75LGI pod- Sep 76 a5 Oe ei Tal — 2533 pod- Sen 77 eye oe Sep 77 Ps Ain INTE \ fEEEEGLES \ LESS RG ' PI A oa ie, NOS Me t Sariasies rik Dies oy S543 “te ee y. ‘S| eg Og: EY Figure 3-10. Dispersai of 7 marked shorejine of Lake Grif 46 47 observed. Prior to the onset of cold weather in late October many one-year old alligators were solitary, although small groups of siblings were still regularly found. Some one-year old animals in all habitats demonstrated movement back towards their first overwintering site at the beginning of the second winter. This was evident with pod 2172 on Orange Lake in 1976 (Fig. 3-7). By the end of the summer this pod had dispersed over a shoreline distance of about 330 m. On 27 October 1976, when water temperature had dropped to 19.5°C, 9 individuals from this pod were found together within an area of about 25 m>. A return of 1.5 year old alligators to their den site was also observed in 1977 on Station Pond, when severe drought eliminated most of the standing water on the marsh. Recapture data from hatching through the first year indicated that there was very little migration of alligators from one pod to ancther, even in situations where pods were relatively close together. The 2172 and 2301 pods on Orange Lake both hatched in 1975, and probably were separated initially by no more than 600 m. Movement eariy the next spring reduced this separation to about 300 m (Figs. 3-7 and 3-8). However, sibling groups remained distinct until September 1976, when one juvenile From the 2172 pod was captured with the 2301 pod. In October 1976, two alligators from the 2301 pod joined the 2172 group and overwintered with them. These 3 individusls represented 8.6% of the estimated 35 ailigators surviving from the two pods for at ieast one year. No shifts were recorded in 1976-77 for five pods on Orange Lake. Two transiocations were recorded on Lake Griffin in 1975-76, representing a total of 6.1% of the estimated 33 one-year survivors from these 5 pods. On Station Pond, } of an estimated 8 one-year survivors (12.5%) was from a different pod; this one animal appeared only after its siblings had vanished, probably through predation. Thus, even where nest densities were fairly high, Fidelity to pod or den site was sufficient to support the assumption that aggregations of one-year-old or younger alligators were composed almost entirely of siblings. For areas with low nest densities, the probability that alligators in a group were siblings probably approached 100%. Dispersal of juvenile alligators following the second winter appeared to be a continuation of patterns of first year dispersal, aithough fewer data were obtained in support of this. Larger animals dispersed farther than yearlings, as shown by plots of two-year dispersal on Orange Lake and Lake Griffin (Figs. 3-7, 3-8 and 3-10). Close associations with the natal area appeared to be lost by about the end of the second year on Orange Lake and on Station Pond, as indicated by recaptures and visual sightings of known-age and similarly- sized juveniles. Two-year old alligators remained dispersed at the begin- ning of their third winter after hatching. Dispersal on Lake Griffin appeared to be slower, possibly as a consequence of reduced growth, but captures and sightings of two-year-olds were few. Two 2-year-o!d alli- gators recaptured on Lake Gritfin had not moved from their first year ranges. The drusny shoreline and extreme wariness of juveniles from Lake Griffin made recaptures infrequent, and probabiy biased the sample; dispersal into fringe areas could have occurred, resulting in iow probability of recaptures or visual sightings. A summary of movement rates calculated from recapture data for the three size classes of juvenile alligators appears in Table 3-4. For size 9°C + £1 4 0 Z 6°h + Z'°2 8 1°99 + Sth LS €*l + 9°0 ral “(Akep/w) sdesay ff JusWwaAocy JO azey SSE[J 2821S Jaqunu aed! pul sasayqueted ul saoquny 4°6 + Z°E e°e + Ol 0 Of + 9° (Aep /w) JUaUaAOW jo a zey (Z)6 (L)1Z (1)9 (8) 04 sdesay # I} ssetg azis *sopeoo! $°0 * 1°O (Aep/w) JUBWAACW jo o7TeY (7)9 (8)98 (281 (91)S61 sdejay ff | sse[g azis *paquasaidas spod jo epl4so[y [e4squed pue yzsOU JUa4eJJIP WOsy S4uoZeHI_Le aytusanf yo JUuaWeAcW jo sazeRYy Baaqnem 4 Urgsjl49 7 ty S,auded PUuUGg UOI7VEIS 7 ebueiug ayeo4 “H-£ PLqeL 50 classes | and !1, only data from Orange Lake and Lake Griffin were sufficient for a useful comparison. Orange Lake alligators moved slightly more than Lake Griffin animals; this difference was significant (p < .05, t-test) for size class !. Larger juveniles from both shallow marsh habitats (Station Pond and Payne's Prairie) had higher rates of movement than alligators in the three lake habitats; the difference between Orange Lake and Station Pond was significant (p < .05, t-test). Extensive movements (over 1000 m between successive captures) by some juveniles in size class I!1 from all habitats suggested that movement rates calculated for this size class were substanti2l underestimates. The extremely low rate of movement obtained from recaptures on Orange Lake probably reflects some bias in collecting. since not all areas of the lake were visited equally. Capture efforts on Station Pond were more evenly distributed. The longest movement recorded in the study was for alligator 20103, a male 82 cm in TL at initial capture. This alligator was captured in the southwest corner of Lochloosa Lake on 7 Gctober 1975, and was recaptured on !7 September 1976 on the east shore of Orange Lake after moving a minimum distance of 5100 m in 346 days (14.7 m/day). Movements of males and females were not significantly different at any of the localities studied. This was not unexpected for alligators in their first year, since these individuals were still in pods. How- ever, larger, more solitary juveniles also demonstrated no sex-related differences in rates of movement. in the largest recapture sample “rom Station Pend, movement of males and femaies was identical (4.5 + - 7.8 m/day vs. 4.5 + 9.7 m/day for 33 male and 18 female recaptures, respectively). Data for males and females were combined in the above comparisons of movement rates between locales. Alligators tracked by radio telemetry moved very little, with one significant exception (Table 3-5). However, instrumentation periods were too short for valid comparisons with mark-recapture data. Movements of alligator 20337 on Orange Lake (Fig. 3-11) suggested that two year old alligators may sometimes travel extensively, and that movement rates calculated from recaptures were low estimates cf actual travel. Number 20337 was probably beginning its third year; the distance it moved in 20 days exceeded the maximum dispersal through the first 2 years for all members of the 2172 or 2301 pods on Orange Lake (Figs. 3-7 and 3-8). Two instrumented alligators were subsequentiy recaptured after their transmitters had failed. The sites of both recaptures suggested that the data obtained during telemetry were representative of the later movements of these individuals. Alligator 20145 was largely sedentary on Payne's Prairie from 23 April to 2] May 1976. It was recaptured on 14 July 1976 approximately 200 m from its last contact, having moved an average of 3.7 m/day in the interim. {ts weight had increased 210 gm (26% initial) from 19 April to 14 July, indicating that food was readily available and that the transmitter package (which was still attached) had not interfered with feeding. Contact with alligator 20089 was lost on Orange Lake on 2! October 1376, and regained when the individual was recaptured 60 m from its last known location on 16 March 1977. Weight loss in the intervai was 7%. waich was consistent with winter weight losses recorded for juveniles of similar size, and the recapture location suggested that little movement had occurred over the winter. 52 *paangdesar Aj quanbasgqns skep i| OZ1 9°8 LL *4dy 72 - “4dv g 71 ebuesg S*h 009£ gol W SQE02 skep QZ O9E 1 0°66 QL “AON H - *290 GI 7 abuesg G 0202 c6 W LEEOZ ushep 9 06 €°ge 9f£ °390 12 - °390 SI 7 a6ue19 cG 0691 88 d 68062 ySAep [2 "of Aew Iz - € 0z 9° “gf “Ady 97 - EZ 4d S,auAeY 5° 018 id J S41 OZ skep g 09 ool SL “AON 9 - *390 LE 4d S,auAed c 604 95 = 8O0LOZ sAep ¢ 0 0 GL °AON € - 390 1€ 4d S,auAeg Aa | n9Ol a7 cs LS2z (Ww) J9e}]UOZ Jseq] OF (Aep /w) pa zyusuNa su, sazeqg uo1zed07 (s4A) (16) (2) XS aquNN, at!1g sangdeg perqiuy JUSWIAOYW , aby “aM yybuaq wory aouRe sig go azey a_qeqoug Leo, *As}owWa[3} Opes Aq pamo,{os suojeBiyppe apruaanr -G-¢€ ayqey saye] ebueig uo Asqowsasaq orpesa Aq pamo, [oy */EEOTH sorebi ple yo sqyuauanoy “EL-€ e4nbir4 SS EX € 3 35 Discussion The effects of habitat on growth rates of juvenile A. misstssippiensis are presumably related to food availability. Prey of small A. missts- stpptensts consists largely of macroinvertebrates and fish (Fogarty and Albury, 1967; Chabreck, 1971; Deitz and Hines, unpublished data). The abundances and availability of these items must vary considerably with water temperature, water depth and trophic state of the habitat. Captive studies of young 4. mtsstsstpptensts have documented the relation- ship between food availability and quality (measured via protein con- version rates) and growth rate (Coulson et al., 1973; Joanen and McNease, 1974). Food consumption by young alligators from brackish marshes is less than that of alligators from fresh marshes, probably leading to slower growth (Chabreck, 1971). £ ! Growth rates of juveniles from other portions of the range of 4. misstsstppiensts are compared with those from north and central Fiorida in Table 3-6. The high rates observed for south Florida alifgaters presumably result from a reduction in or slimination of the winter dormancy period (Hines et al., 1968). Orange Lake aliigators growing for 12 months at the same rates observed for the 7 menth active season would have an annua! increment in total length of approximateiy 36 cm-- rcughly the same growth as Everglades animals. Seasonal influences on growth are also illustrated by Murphy's (i976) data from South Carolina, where juveniles grew faster in artificially heated portions cf 4 lake BI g ; than in unheated parts (Table 2-6). Prey availability is undoubtedly guite variable both within and between iccales, as well as seasonally. zZ61 ‘eseg 9f61 ‘Aydanw +1 9Z6t ‘Aydanw “1 "Apnys siyy "Apnas sty “Apnas Siyt HEGL ‘AuUaYt OW 89GI ‘°722 7a sautH 20.4n0S "S'N UsaISsYyINOS 94} YnoYbnosy "€G SEM SpeWyUe Pug Jed [Le 4OJ az1S aj dwes | 1"He (4A/w2) quawetouy eZIS jLenuuy peleey ‘puog seg - puodg Jeg - UPJS IAD 1 - puog uol eqs - “| abuesg - sape,Buaaqz - uo} eda} sisuarddississqm 407P6177¥ 4O seze4 yIMoINH *g eULf,OIeY eulpoue) eulpouey epl4sol4 PPltol4 eplsol4 euelsinoy Epl4sol4 -€ 91qeL ¢ » 57 Growth rates for most other crocedilians have not been determined. Growth rates (converted to increment in total length)of Crocodylus porosus in northern Australia averaged about 36 cm/yr for males and 33 cm/yr for females (Webb and Messel, unpublished data). Seasonal variations were not as pronounced as in A. mtsstsstpptensts. Rates for C. ntlotteus from east Africa reported by Cott (1961) from various sources were slightly below the 31.7 cm/yr increase in total length determined for captives. Other data for C. niloticus from Graham (1968) suggest that sub-optimal habitat reduces growth considerably. Males grow faster than females in Crocodylus porosus (Webb and Messel, unpublished data), C. ntlotteus (Graham, 1968) and A. miests- stpptensts (Mcilhenny, 1935). Differences in growth rates of Louisiana A, mtsstsstpptensts are probably not significant until juveniles reach conclusions for Florida alligators. Juvenile alligators are sometimes difficult to sex; Hines et al. (1968) have reported 80% males in their south Florida sample, a figure which they believed to result from sexing errors. The sex ratio determined for north Florida juveriles (1.59:1) fs in excellent agreement with the sex ratios of Louisiana adults (1.5]:1- Chabreck, 1966). Survivorship of juvenile crocodilians is unknown, but has deen widely assumed to be low. Popular and semi-technical accounts of A. misstsstpptensts report mortality to be 90% or more for the first year (Neill, 1971); the few data available indicate that it may be signif- icantly lower. My estimacres probably represent minimum figures for survivorship, since many juveniles which were known to be alive 58 (subsequently captured) were not captured or seen on some visits to their pods. The two-year survival of 2 pods in South Carolina was approximately .16 (Murphy, 1976), which is comparable to my figures. Nichols et al. (1975) estimated one-year survivorship of Louisiana alligators to be .35 and two-year survivorship to be .21, although ne supporting data were provided for these estimates. The survivor- ship of one Louisiana pod marked in 1921 was apparently at least .66 through 1927 (McIlhenny, 1935). Quantitative data on survivorship in other crocodilians are available only for Croeodylus porosus in northern Australia, where the one-year survivorship of one cohort of 58 hatchlings was at least .40 (Webb, 1977). Observations by Graham (1968) for ¢. ntlotteus indicate that where habitat is unsuitable for juveniles (bare shoreline) mortality may be nearly 100%. While not statistically significant, the differences in survivor- ship between habitats suggested differences in predation. This is supported by the Frequency of injuries, which, like mortality, was highest in shallow marsh habitats. This pattern implies that wading birds are an important predator; their access to sma}] alligators is probably much better in shallow marshes than in deep water areas. Wading Dirds are known predators of other juvenile crocodilians such as Crocodylus niloticus (Cott, 1961) and C. palustris (Dharmakumarsinhii, 1947), and have been observed preying on juvenile alligators at the Carr pond (Carr, pers. comm.). Droughts are more jikely to increase mortality of marsh alligators above that of lake alligators (Nichols t al., 1976); this could be by desiccation or result from increased access by predators. Drought mortality of subadu!ts on Station Pond 59 in 1977 was severe (Himes, Woodward, and Deitz, unpublished data), and Staton and Dixon (1975) attributed low survivorship of some Catman crocodtlus in Venezuela to drought. An age-related increase in the natural incidence of injuries similar to that observed for A. misstsstyptensie appears to be typical for other juvenile crocodilians as well. I!njuries to hatchlings and juveniles less than about 1 m in total length have been assumed to represent predation, while injuries to larger juveniles and adults are attributed to social interactions and, possibly. attempted cannibalism (Webb and Messel, 1977; Staton and Dixon, 1975). Fiuctuating water levels concentrate Catman crocodilus populations and increase social conflict (Staton and Dixon, 1975, 1977); this could account for the higher frequency of injuries in marsh-dwelling A. misstssipptensis. However, alligator population densities on Orange Lake and Lake Griffin were as high or higher than on Station Pond (Hines, Woodward and Deitz, unpublished data), and the high incidence of injuries on Station Pond was recorded prior to the 1977 drought. Evidence for significant cannibaiism in A. mtsstsstpptensts is likewise poor, as will be discussed below (Chapter 5). The movements of juvenile A. misstsstpptensts in north Florida correspond closely to those of Louisiana alligators with respect to movement from nest to den, overwintering, and the initiation of dispersal 1935; Chabreck, 1965). Chabreck (1965) W = oO at o 3 a << the following ssrin has also described reduced movement of pods when nests are located adjacent to dens, as well as the movement of pods to open water when nests are situated nearby (similar to my lake fringe nests). The importance of the female's guard pool or wallow in determining post-hatching movements has not previously been emphasized. In addition to possibly providing deeper (and cooler) water for the adult during attendance of nests and young, the wallows may be important in providing a smal! but locatable refuge in which young can assemble after hatching. Pools created by females during movements of the pod to the den may similarly aid in assembly, and function to minimize losses of stragglers. While these pools could increase the chances of predator detection, particularly by wading birds, this may be offset by the increased visibility of young which they provide the attending parent. Smashed vegetation provides basking sites for the hatchlings; in some areas of marsh these are not readily available. Hatchlings in pools are also able to disperse more during nocturnal feeding without entering dense vegetation (see Chapter 4); this may facilitate foraging by in- creasing range and also by improving access to insects which would otherwise be unobtainable on plant stems above the water. Dispersal of juvenile alligators during their first summer, foi by returns to the den during the second winter or during droughts, has also been reported by Chabreck (1965) for Louisiana and by Fogarty (1974) for the Everglades. From comparisons of Lake Griffin and Orange Lake, | suspect that pod dispersal is related to size in all habitats and occurs more slowly if growth is retarded. However, mean movement rates computed for individual recaptures (Table 3-4) did not correlate well with growth rates. Movement rates of size class I1! juveniles indicated that alligators of this size have lost permanent contact with their natal] areas. 61 Movement of immature alligators in Louisiana decreases from spring through fall, with males exhibiting slight preferences for open water areas and females for marsh (McNease and Joanen, 1974; Taylor et al., 1976). Both sexes show wide variation in daily movement, and occasional long movements (1 km) are regularly observed. My observations of juvenile movements based on recapture data from Florida are consistent with these patterns. Sex-related differences are not evident in small juveniles in Florida; the juveniles tracked by McNease and Joanen (1974) were larger (mean SVL 73 cm), which is probably significant. Wallows or guard pools are also used by nesting female Crocodylus porosus; the photograph by \ bb et al. (1977) of a nest in northern Australia shows walliows which appear identical to those used by 4. musstssipytensts on Orange Lake. Small pools are also reportedly used by adult C. palustrts (Dharmakumarsinjhi, 1947) and C. ntlotteus (Cott, 1961) in caring for their young. For C. niloticus, use of these poels may requireoverland movements of female and young from river bank nests to suitable inland sloughs (Cott, 1961). The semi-permanent habitat alterations produced by A. misstssipptensts in making dens and trails (Mclihenny, 1935; Craighead, 1968) have not teen reported for other crocodilians, although C. ntlotieus and Catman crocodylus will deepen poois in response to drought (Cott, 1961; Staton and Dixon, 1975). #arental care is sufficiently widespread in crocodilians (see Chapter 4) that permanent nursery areas such as those used by Station Pond alligators may be formed by the reproductive activities of other marsh-dweiling species. 62 Australian Crocodylus porosus form creches (= pods) after hatching, and in some cases these are moved or accompanied by an adult (presumed parent) for several weeks (Webb et aZ., 1977). Subsequent dispersal of C. porosus hatchlings occurs earlier than in A. misstsstppiensts, and distances moved by one- and two-year old juveniles are much greater (Webb and Messel, 1978). Tidal currents in the rivers where these groups were studied are evidently significant, since there is some tendency for animals to disperse downstream (Webb anc Messel, 1978). Medem (197la, b) has suggested that Paleosuchus palpebrosus hatchlings, which generally occupy swift streams, also disperse rapidly without forming large pods. Occasional long distance movements similar to those observed in individual A. mtsstsstpptensts also occur in juvenile C. porosus, and these have been postulated to represent excursions which are followed by returns to a core area (Webb and Messel, 1978). Juvenile 4. misstsstopiensts apparently possess homing abilities sufficient to allow such returns (Chabreck, 1965; P. Murphy, 1978; G. Rodda, unpublished data). CHAPTER IV SOCIAL BEHAVIOR OF JUVENILE ALLIGATORS Introduction The recent world-wide interest in crocodilian conservation has resulted in many new observations of crocodilian behavior. Enough infor- mation on adult social behavior has accumulated for 3 species (Alligator mitsstsstpptensts, Crocodylus acutus, and C. niloticus to support valid interspecific comparisons (Garrick and Lang, 1977), although compre- hensive field studies of adult behavior such as Modha's on C. niloticus (1967) are still lacking. Attempts to breed most crocodilians in captivity have produced surprising new data on nesting and parental care (2.g., Alvarez del Toro, 1974; Hunt, 1975; Pocley, 1977) and suggest - that recently discovered behaviors such as parental transport of young . ! in the mouth may be a consistent feature of the order. Descriptions of juvenile social behavior in crecodil'ans usually have been confined to observations that the young of most species remain in groups for some period after hatching. Vocalizations have been presumed to be important in maintaining these groups (Campbell, 1973), but the actual maintenance behaviors and duration of groups have not been systematically studied. Whiie some parentai care of groups of yourg has been regularly observed in captivity, the consistency, duration ard significance of parenta!l care in wiid crocedilians are largely unknown. Parental care for 5 weeks after hatching has been reported for Crecodylus cay od 64 acutus by Alvarez del Toro (1974); Cott (1971) has observed 12 weeks of post-hatching care in C. ntloticus. Mcllhenny's (1935) observations of A. mtsstsstpptensis indicated that pods persisted until the following spring, suggesting that they were actively maintained, and were protected by the parent female through- out this period. These observations were imougned by Neill (1971). However, both Chabreck (1965) and Fogarty (1974) also reported pod persistence for one year, and Kushlan (1973) provided unequivocal evidence for maternal protection of the young. The objectives of this portion of the study were to obtain additional data on the social behavior =H r 1 of pods and the quency of parental care and, by examining pods in different locales, to determine the extent to which these might vary with habitat. The significance of vocalizations in maintaining pods and mediating parental care was also investigated. Methods General locations of pods were determined as in Chapter Iil. Diurnal observations of pods were usually made with binoculars from within 10 m; smail alligators could be observed successfully without 4 blind from this distance if observer movements were reduced to ea minimum. Temporary blinds were occasionally used, out frequenz position snifts by pods made their regular use impossidle. Juveniies so successfully observed from ar airboat seat; it appeared that movements made high (2 m) above the water surface were not easily detected. OCBetailed observations of nocturnal behavior proved impossibie. Passive night vision equipment (starlight scope) was used on severa! occasions, but resolution and image intensity were both too poor to distinguish juvenile alligators from emergent vegetation. General movements and behavior of juveniles after dark were recorded by flashing a headlamp beam at regular (usually 15 minute) intervals and noting positions and any other activity of alligators visible. Eyeshines (reflections from the tapetum lucidum) were helpful in locating alligators in dense cover. Flashes of 15 seconds or less appeared to have little effect on movements or rates of vocalizations; longer flashes seemed to produce some avoidance and cover-seeking behavior and were avoided. Some nocturnal observations were made by covering a headlamp with a red filter (auto taillight cover). This light had limited range and produced dim eyeshines at best, but it was also far less disturbing. Many indgividuais appeared entirely unaffected and continued to move and feed in an apparently normal fashion while the red light was on. Positions of individual juvenile alligators during the day were recorded at regular intervals. Each animal was scored as: 1) moving or stationary; 2) on land or in the water; 3) in the sun or shade; and 4) uncer cover or in the open, t.e., relatively exposed when viewed from above. Verbal descriptions of important physical features as wel! as Jy 4 field sketches were made to assist in plotting movements. Jadividi recegnition was possible for some juveniles that had anomalies in their banding patterns. The vocalizations produced by hatchling alligators have been referred to as grunts by Campbeli (1973) and Herzog and Burghardt (i9 These grunts were quite audible at most distances from which | observed ? i pods. Grunts frequenciy occurred in bursts of one or more single grunts 66 produced in rapid succession by one individual; following Herzog and Burghardt (1977) each of these groups of grunts was ccunted as a single series. The number of vocal series produced during each 10 or 15 minute period was tabulated; if the individual vocalizing was seen, context was also recorded. Each pod received a score for number of vocal series/alligator-hour (VAH) for each period, calculated in the following fashion: the observation period period length in hours) VAH = # vocal series durin # juveniles known to be present Differences in frequency, intensity and tocation between vocalizations of different individuals were such that scoring was difficult only if a large number of individuals were vocalizing simultaneously. Tape recordings of vocalizations were made with an AKG 451E directional microphone and a Nagra I1!8 or Tandberg Model 11 tape recorder, and analyzed with a Kay Sonagraph (Model 7029A). Results Activity Cycle At sunrise, small alligators were in the water, usually in dense cover such as emergent Cladiwn or Pontederia stands. Little activity was evident at this time; those alligators whicn were visible remained motionless and seldom vocaiized. Emergence from cover began about one hour after sunrise (Figs. 4-lb and 4-2b), and appeared to depend on iliumination by the rising sun of portions of the small coves where hatchlings were located. Prior to emergence, a few juveniles would begin to swim about ana emit low intensity juvenile grunts. The number 67 {6 SEPT. i977 30 SUNRISE AT O714 I8 ANIMALS OBSERVED Ir 20 4 2 i ie) . 100 ae we an 20 \ on "\ no. visible © 75 / 15 is” 4 me 4\ a cna | 1 0730 0800 0300 ee rs) 1000 OO TIME (EDT) Figure 4-2. Morning emergence by hatchling alligators on Payne's Prairie. TOTAL NO. VISIBLE 68 69 of grunts by seen and unseen hatchlings rose rapidly at this point (Figs. 4-la and 4-2a). As most aliigators in a group began to vocalize sporadically, the first few individuals emerged from cover and climbed out of the water onto tussocks or clumps of vegetation in the sun, grunting regularly as they did so. The rest of the pod followed immediately, climbing out into the sun while grunting. Most of these hatchlings used the same tussock or clump of weeds as the first individuals to emerge. Alligators ceased vocalizing once they had climbed out of the water and moved onto a suitable basking spot. At the time of emergence, site air temperatures were almost always equal to or greater than water temperatures. The movement of the group from aquatic cover to terrestrial basking sites usually took less than 30 minutes and was often completed in 15 minutes (Figs. 4-1 and 4-2). As indicated above, alligators oriented te basking spots already occupied by other pod members, even though there were often many other apparently suitable sites nearby. This resulted either in one large aggregation of basking alligators within an area sometimes as smal! as | i” or if small clumps of emergent vegetation were being used, in two or three smaller groups adjacent to each other. datchlings that remained in the nursery pool by the nest Frequently basked on the base of the nest; those which hed moved into other pools used vegetation which nad been flattened down by the femaie's body. If the female was present and remained stationary in che sun, hatchiinas sometimes used her head and back as basking sites. Cloudy skies or coo! temperatures delayed or inhibited this coordinated morning emergence. |! made no systematic observations of 70 pods in mid-winter but hatchlings which were observed basking at this time of year were as tightly bunched as on other occasions. Following morning emergence, juvenile alligators basked for varying periods; the duration of those was probably dependent on individual thermoregulation. For most hatchlings, the period on land lasted about 2-2.5 hours, and included movements between sun and shade (Figs. 4-Ib and 4-3). Little movement and few vocalizations were evident in the group during this period; VAH for 8 pods observed on 14 sunny days averaged 2.3 + 1.7. Alligators were quite tolerant of being stepped on or jostled by other juveniles while basking, and it was not uncommon to see individuals basking with the heads or tails of others lying across their backs. Some hatchlings appeared almost comatose, and were observed to lie motionless and fully exposed to the sun for 30 minutes cr more with their eyes closed. Hatchlings would also occasionally climb up the stems of emergent vegetation, especially Cladium jamatcensts, while basking, and ! observed some that had climbed more than 30 cm above the water surface. After basking, hatchlings moved into shady areas on land or in the water (Fig. 4-4). These movements were accompanied by sporadic vocal- izations. While movements off of the basking platforms were not as concerted as emergence, most alligators left within about | hour of one another; this usually took place from 4 to $ hours after sunrise (see Figs. 4-3 and 4-4). Overheating may have been the principal stimulus for these movements, since the alligators selected cooler areas and air temperatures at this time often exceeded 30°C. However, | rarely observed obvious behavioral thermoregulatory responses, such “Aep jo Sawi} YUs4es4JIp ye 497eM ay} UL Suojzebi pe Burjyosiey jo a6equa.seg *¢-y asnb14 fon) JaSUNS s10jaq SuNOHY {OSUNS JOLD SUNO}Y Ol az o¢ Orv os ' aos OL i PSHUNS 4S] 4,0 sano O'e= Ol- SS Z 0'9 O'S O'b Oe Oz OO; NS ame ci a a 0—1— 90 -whr a fee!—__1———+- G t Zz £ 1 ! 2 ° cee ia o® *e e oF ® ee ee e eo # e ® e °,0 ® Pe e * @ 9 eo” oo ~ OZ a“ oe e@ ® > 9 9 ” 2? % a - Ob % ee” - | 2 e e e rT c & : 2 o- e ® - O9 ’ * e o® e ° | C) Oa o 8 i) ® 6 » @ ® e eka ¢ t @ e8 eereskQO0 we om es eeoe @ eeteoe oa ®e @¢ @ ¢ oF ool O°H NI % 73 "sanoy Bulusow ayy Bulanp Buryseq 40 49000 sapun saoqzebrype Burpyouey yo uolinaraysig “We BING SSIYNAS YALAV SYNOH 9-GG< SG-c&KS-SP | \ a JIMNVS JO LNFOY¥3d ae > % ~ a % em Pa 4 “N aN aN =e os " oO 74 as postural! adjustments, that would support this supposition; gaping was only rarely observed. Some hatchlings and larger juveniles yawned briefly once or twice before entering the water, but this also was infrequent. During warm weather, young alligators spent most of the remainder of the day in the water, generally remaining under the cover of floating or emergent vegetation and moving occasionally. As noted above, basking was prolonged in cooler weather. Throughout the afternoon some alligators climbed out of the water to bask briefly or to lie in the shade, but tnere appeared to be no group coordination to these movements and most pod members remained in the water (Fig. 4-3). Short movements by individuals gradually dispersed the pod as the day progressed, and the hatchlings were never as densely aggregated as during the morning basking period. Vocalizations were few; VAH for the midday - sunset period averaged 2.4 + 1.3. Although alligators were relatively inactive, they responded readily to potential prey and feeding strikes were regularly observed at al] hours. By sundown, a!! individuals in a pod were normally in the water, under cover and largely motionless. Immediately after sundown there was an increase in activity which duplicated the morning emergence in its rapid, synchronous onset. The number of alligators moving and grunting rose steeply over a 15 minute geriod, and as these juveniles began swimming around they also emerged from cover. Figs. 4-5 and 4-6 are representative temporal plots of the rate of vocalization by the pod (VAH) and number of alligators visible to me. In Fig. 4-5 grunting oeaked before most of the pod became late ON a bt li | |- ‘ayey ebueig ‘pod ¢¢o// 342 Jo aouabsoua Buyusag G-h 24nb14 (103) 3WiL Z¢ 6] J8SUNS O€le Gll2 OOI2 SvO2d ocd? GIO2 0002 Sbé6l ; ‘eceneneaeeen aan mama aie O ig Se eae “~ HYA OS OOo! OG! ~On B}qISiA ON — | TH ag es as a se att cee o77 002d G3AYISEO SONITHOLVH €2 God ¢¢ & LL L261 1dJS 8 OGe HVA sayey o6ueig ‘pod 4,-// e471 jo asouabsowa Buruaagz “9-H a4nb14 77 JTIEISIA YSEWNAN TWLOL i's) O02 Otl2 OO12 Or02d (sanoy) AVG 40 3WIL / ~~ FA J1GISIA NBBWAN SS / a visible--it appeared on this occasion and others that hatchlings began swimming about while vocalizing and then emerged from cover. An increase in feeding strikes was also associated with these increased movements and feeding continued as the pod rapidly dispersed. Alligators vocalized as they moved, and for the first hour after sunset mean VAH was 8.8 + 6.9, significantly higher than mean VAH observed for the morning or afternoon (p < .01, t-test). Thereafter, vocalizations declined; this was coincident with a decrease in feeding activity and swimming move- ments. Figures 4-7 and 4~8 are representative plots of the positions of most of the members of one pod on Orange Lake during nocturnal emergenc Tne rapid dispersal following emergence is evident. The jimits of dispersal were approximated by the end of the first hour after sunset, although some individuals continued to move away from the center of the group for the next few hours. By 0030 hours feeding activity had ended, and alligators had moved into or adjacent to vegetation along the nearest shoreline (mostly Hydrocotyle wnbellata in Fig. 4-7). Little additional activity was seen until O445 hours when the hatchlings began returning to their initial emergence point, disappearing into the vegetation when they arrived. In contrast to most other movements, these were not accompanied by an increase in vocalizations. By 6615 the distribution of the pod had contracted to a 20 m strio of shoreline m + hy io) y ? 83 "wo €1-Zt IAS ‘s7suazddississi1iu 409PH277¥ JO SyunsB ayruaanf Ajyisuaqui-mo, yo ydesbosqoads punos "Ol- e4nBiy SQGNODdS NI JWIL ee eee en ee ee ee ee = Ny 89 "Wd €1-Zl IAS ‘szsuazddississi *y JO squni6 ajruaanf Aqysuaquli-ybry yo ydesboaqoads punog "14-4 a4nbry SQGNOD4AS NI JWIL ZH "(¥xe1U0D Sse4isip) WO Z] WS ‘szsuerddississ pu ‘y @,lueanf ppay-puey e yo syyeo jo ydesBouqoeds punog ‘ZI - e4nbl4 SGNOD4S NI JWIL i) | | | ! + N ZL ‘Oo se) Sil "669 ue ulory szsuazddiseiesq *y peysjeyun ue jo sqpeg "€[-h a4nbiy4 SGNOOD4S NI JWI L Cee ee Se ae a A ee ™ ~. oN 92 Distress calls were emitted in rapid succession when juveniles were alarmed by my approach and when they were captured. In some instances, they resulted in the approach of adult alligators, assumed to be the female parents (see below). The behavior of other juveniles upon hearing calls emitted in these contexts was quite variable; my observations were complicated by the fact that it was often impossible to determine whether the alligators were responding to the distress calls or to the original disturbance. Many juveniles, whatever their sub- sequent behavior, vocalized in response to distress calls (as did many in response to juvenile grunts). Some juveniles appeared to be alarmed, and responded by submerging or by swimming or running into cover. Others responded by moving toward the source of the calls. This Jast response was so consistent that it was sometimes useful in capturing juvenile alligators. Distress calls of captives could be elicited by Squeezing them or by agitating the bag in which they were being kept; many of the remaining pod members would then emerge from vegetation and approach. Older juveniles could also be attracted in this fasnion, although not as regularly as hatchlings. Submerged hatchlings surfaced in response to calls of hand-held siblings, indicating that the calls were audible underwater. Although vocalization appeared to be of great importance in main- taining pod cohesion, visual contact was clearly an important close range signal. Moving hatchiings were often fol lowed closely by other hatchlings. As noted above, the first hatchlings to emerge from cover in the morning were followed by the remainder of the pod. Juveniles normally swam with only a small portion of their back exposed; they 93 were never observed to inflate sufficiently to expose more than this. The distal half of the tail was allowed to protrude, so that both the head and tail of hatchlings which were swimming or resting in the water were visible above the surface. This posture was identical to the head-emergent tail-arched posture described by Garrick et al. (1978) for adult A. misstsstpptensts. In hatchlings, the posture was probably used to increase visibility of individuals to other pod members or to the parent; it appeared to have no other social significance. The tail was submerged and only the head was visible when hatchlings were alarmed or concealed under cover. No structured social organization was evident in pods. Those which emerged first to bask were different individuals from day to day. Hatch- lings were extremely tolerant of close contact. An individual would occasionally grunt if stepped on, but more frequently would either ignore the disturbance or move over. By July of their first year pods of juvenile alligators were much warier of my approach and more difficult to observe as a group following dispersal. Consequently | have no quantitative data on rates of grunt- ing in different social contexts by animals older than | year. Yearlings and older juveniles which were observed feeding at night vocalized rarely; this was markedly different from what was observed for hatch- lings. Yearlings were heard grunting during emergence from the water to bask, when approaching or approached by an adult alligator, and when Startled by my appearance. They also grunted while swimming with smal} grouss of other yearlings; vocalizations in this context appeared to be used to maintain contact since these individuals answered each other's grunts. 94 One-year-old alligators were observed in the midst of many pods, and one yearling was captured twice with the same pod. Yearlings observed with pods of hatchlings were of normal size for their age. These yearlings emerged, basked, and foraged along with the hatchlings, but grunted infrequently during these activities. Parental Care The amount of parental care that pods received was extremely variable in nature and in duration. The shyness that most adult alli- gators in all habitats exhibited towards humans made direct observation difficult; for reasons discussed below | regard my assessments of the degree of parental care of different pods to be minimimum estimates. With one exception (see below), only a single adult alligator was ever observed in close association with a pod of hatchlings. The only adult alligator at the Carr property was known to be a female; her behavior was consistent with the behaviors of other protective and attentive adults, and | follow Mcilhenny (1935) in believing all such alligators to be female. | used three artificial categorizations for female parental behavior in 4, mtsetsstpptensts: minimal care, attendance, and defense. Pods that received minimal care included some with which females were sighted on ane or two occasions, but most minimal care pods were never observed with an adult alligator. Females were considered attentive if they were present on at least one-third of all observations of the pod but did not threaten humans when the pod was approached. Defensive females were those which actively threatened me when | approached a pod and/or attempted to capture the young. 95 It appeared that most if not all pods in the study received some parental care. The appearance of all successful nests on Payne's Prairie and on Orange and Lochloosa lakes indicated that they were probably opened by the female (Deitz and Hines, in press) and the pods were probably then led or carried to the guard pool (Meyer, 1977). The role of the female parent in subsequently creating additional wallows and trails which determined movements of the pod has been discussed above. There were evidences of regular adult alligator presence (t.2., trails, tracks, recent excavations, smashed vegetation) associated with most pods where | never actually observed adult alligators. Approximately one-third (34%) of the pods encount red in this study were cared for by attentive or defensive Females, although this composite figure was biased by differences in female behavior between locales (Table 4-1). The major difference between attentive females and al! others observed was apparently their reduced shyness towards humans and/or boats. Eight attentive females were observed on 22 occasions. During 9 encounters (41%) females remained largely motion- less while | observed the pod, and submerged only when | approached to within about 10 m. On 8 occasions (36%), females submerged immediately after my arrival. Two females (9%) initially moved toward their pods Dut submerged when | continued to approach, and on three additional encounters (14%) females responded by submerging, returning to within about 10 m, submerging, returning again, etc., for the duration of my visit. Postures and threats such as those used by defensive female alligators were not observed. Defensive female alligators protected their pods with a series of threat displays directed towards me. if ignored, these displays Table 4-1. Locale Payne's Prairie Orange Lake Lake Griffin Lake Wauberg Station Pond Biven's Arm Carr property pond in south Gainesville Total Parental care of hatchling alligators. Pods Observed 13 20 1] 59 Type of Care Minimal Attended Defended 7 3 3 6 14 4 2 6 10 | 0 ] 5 9) 2 0 3 3 3 3 39 (66%) 10 (17%) 10 (17%) 20 96 97 culminated in approaches by the female which, if not actual attacks, were sufficiently menacing that | ended the encounters by retreating. | provoked 24 encounters with 9 different defensive alligators; two of these alligators were observed with pods in two separate nesting seasons. Upon observing my approach (usually by wading) near their pods, defensive females swam toward me with their bodies inflated. This elevated their dorsal surfaces several cm above the surface of the water, and this posture was easily distinguished from the normal Floating or swimming posture where the dorsum was but slightly emergent. Females normally halted 5 or 10 m away from me in the inflated or head-emergent tail-arched posture (Garrick et al., 1978), and were at this point usually closer to me than any of the hatchlings were. If I continued to approach or remained stationary, from one to several loud hisses were emitted. Females were stationary as they emitted these hisses; the head was elevated out of the water and pointed toward me, the snout was lifted and the jaws were from slightly to widely agape. This posture was identical to the bellow-growl posture described by Garrick et al. (1978, Fig. 7A) although bellow-growls were not heard. One female thrashed her tail from side to side while hissing. If 1 attempted to move to one side, females oriented their heads to follow my movement and then repositioned their bodies. Subsequent behavior was variable. If | remained stationary, some females withdrew to their pods within several minutes, while others maintained the bellow-growl stance or head-emergent tail-arched posture and continued to hiss. Advances by me were met with renewed hissing and jaw gaping. During one nocturnal 98 encounter, a female bellowed twice at me from less than 5 m away. Females lunged at me twice with jaws opened wide; one of these animals then pursued me for approximately 10 m. Although defensive females sometimes responded to my approach before any reaction by the pod was observed, distress calls by the hatchlings were clearly important in stimulating female protective behavior. | was sometimes able to approach and observe defended pods without being detected by the female. When these hatchling finally became alarmed by my movements and began grunting, the female appeared immediately. Females in these situations seemed initially to swim toward the vocalizing hatchlings and appeared to orient to me only after they reached the pod. On three occasions | captured hatch!tings from defended pods; these hatchlings grunted continuously after capture. This provoked extremely rapid approaches by all three parents. In contrast to other encounters (which, except for the one pursuit described above, ended with my retreat from the vicinity of the pod), these Females all pursued me as | retreated with hatchling in hand. Two of the females followed me out of the water up onto the bank, and the third pursued me for approximately 10 m through shallow marsh. After all three of these alligators had reached the limits of their pursuit, ! returned and released the captive hatchling between us. In all three cases the hatchlings (which continued to vocalize) were ignored. In addition to exhibiting threats toward humans, defensive female alligators were nore consistently present with their pods than attentive x females. Females were present at 38 of 39 visits (97.4%) to 6 defended pods, but were observed on only 20 of 37 visits’ (54.1%) to 6 attended pods (p < .01, Chi-square test). The behavior and regularity of both attentive and defensive females with their pods was similar to their behavior at their nests during incubation (Table 4-2). All pods from nests that were undefended received minimal care. There were no evident differences in distance of pod movements, use of additional wailows, or timing of movements from nest to den between pods which received different degrees of protection against humans. There were also no significant differences in first-year mortality between attended or defended pods (n = 3, for pods with reliable data) and minimal care pods (n = 20), although sample sizes were quite smail and these comparisons were made across different locales (see Chapter i11). Two adult alligators were observed with one Orange Lake pod on 6 May 1977 and again on 20 May 1977. The length of the larger of these adults was estimated at 3.0-3.4 m (10-11 feet); it was assumed to be a male on the basis of size (Joanen et al., 1974) and behavior (Garrick et al., 1978). Courtship was observed between these two adults on 6 May; | assumed but could not be certain that the male observed with the presumed female on 20 May (same location) wes the same individual observed on € May. On both dates, hatchlings were ignored by the male and did not respond to his presence. The only reaction that | observed were sporadic grunts by some individuals in association with movements of the adult; some hatchlings moved slowly out of the path of the male as he swam past them. Tre duration of parental care by attentive and defensive females was variable (Table 4-2). All attentive and defensive females appeared 100 uoleDIuNWWOS *Saed S4api4ag -q €/e ‘a ¥(d) aye] S,UBUMaN 9L (Yo! JedtunwWOd *s4ad f44e9) Qf *390 97e| €/é ‘a Z/z ‘a Ase) g/ GL Bujsds ul aaysuajap you g - 4L *390 42 El/ElL ‘dQ = gz/gz ‘a 41e9 hl z/z ‘a h/y “a dd tad gZ eure hz €i/et ‘a o/s ‘a dd Lisl LL Bbujads ul quasqe g - gf “AON § 8/h ‘Y 6/y SW dd 9099L GZ Sulsds ul quesqe § - / *390 4Z 01/5 ‘WY oOl/9 ‘Y¥ dd 1g9SL yZ °220 ZI S/S “da 02/61 ‘a dd PASTA — pangasqg Aegaseytst~S~S POd YIM ISON IWS~™~CYLDI "FON 159N pue sea, Jo1Aeyeg apeua, "SJISIA [P}07/JUaSa4Id seM ajeulsy YOIYM UO SUOISe990 Jo sdquwnU au4e Jo;Aeyeq 4a}4e Staquny “aA1SuaJop = Gg f9A}}U9zIIe = Y :s4olAeyag *spod y2IM pue szseu ye paasasqo suojebi, je apeweas Jpnpe Jo soraeyog "Z- PLqeL 10] to care for their pods from hatching to the onset of cold weather; analysis of the tovements of minimal care pods suggested that they too had some association with the female throughout the first two months following hatching. Some females remained in close association with their pods through the following spring, while others clearly did not (Table 4-2). The latest date that maternal pod defense was observed was 24 June 1977. The defending female on this occasion inflated her body and swam directly at me as | approached--a response consistent with my other encounters with this female. One pod on Orange Lake (not shown in Table 4-2) was regularly attended through 20 May of the year following hatching. Pod attendance or defense also varied with locale (Table 4-1). Differences in the extent of human disturbance (and possibly, therefore, harassment of alligators by humans) between these locales seemed the most likely explanation for this. Payne's Prairie had been a state Preserve and closed to the public since 1971; furthermore, long-time residents of the area agreed that during private ownership of the Prairie trespassers were probably more often molested than alligators. Orange Lake, Lake Griffin and Lake Wauberg were ai! regularly used by fishermen and punters. However, there were large portions of Orange Lake that were normally inaccessible to most boats; this was not the case on Lake Griffin or Lake Wauberg. Human-a!lligater contact on Station Pond was presumably minimal, but too few pods were observed for valid comparisons. Biven's Arm, the pond in south Gainesville (beth within the Gainesville city limits), and the Carr property were localities at which alligators Frequently encountered humans but were 102 not exposed to motorboats and probably received little harassment. Most of the pods in these three areas were attended or defended (Table 4-1). Although sample sizes were smail, there was no indication that duration of pod attendance was correlated with habitat. As discussed above (Chapter Ill), dispersal of pods began at about the same time in all areas. Discussion The activity cycle of wild Alligator mississtpptensts appears to be typical of that reported in studies of thermoregulatory behaviors of other crocodilians. Synchronous emergence from the water to bask has previously been reported for both adult and juvenile A. mtsstsstppiensis (Lang, 1975a, 1976) and Crocedylus niloticus (Cott, 1961; Modha, 1968). After basking, a return to the water for the remainder of the day with occasional brief re-emergences is also characteristic of other croco- dilians studied (Cott, 1961; Modha, 1968; Lang, 1975a; Johnson, 1973). Two to four-year old 4. misstsstoptensis in outdoor pens in Florida studied by Lang (1976) emerged at sunrise and remained on land until sunset; my observations of wild juveniles of this age suggest that later emergences in the morning as well as an earlier return to the water are typical under normal conditions. Social coordination in the timing of emergence from cover and movement to land has not been oreviously reported for any crocadilian. The most striking consequence of the rapid peak in vocalizations as juvenile A. mississtpptensts emerged from cover and moved to a common basking site was the close aggregation of pod members. Similar behavior 103 may occur in Crocodylus ntloticeus, based on the observations of Modha (1967, p. 94) that hatchlings of this species basked in clumps with ''four or five animals sitting on top of one another.'' While some reaggregation occurred in the early morning hours Following a night's feeding, pod members were still scattered at sunrise, and some individuals were 10 m or more from the main group (see Fig. 4-8). The morning vocalizations produced 4 sustained signal which probably enabled most stragglers to locate the main group. Diel basking rhythms have been reported for juvenile A. misstsstpptensts (Lang, 1976) and C. ntlottous: there is no reason why isolated juveniles could not predict the approxi- mate timing of these vocal peaks and be prepared to orient to the group when they were heard. Isolated animals could generate additional vocal cues, if needed, by grunting and orienting toward the subsequent vocal responses. The similarities between the re-~aggregations following disturbance of the pod and the social bask also suggested that these choruses of grunts helped to achieve pod cohesion. Individuals vocalizing as they emerged from cover were likely to be answered by other nearby juveniles. Moving individuals were likely to continue vocalizing even if unanswered. The most likely orientation of individual alligators responding to the grunts of others would therefore be toward the largest concentration of juveniles. Pitman (1936, in Cott, 1961) referred to increases in vecalizations by hatchling Crocodylus niloticus as they regrouped after disturbances. The rise in VAH associated with evening emergence may also promote pod cohesion, although a rapid dispersal of feeding individuals 104 followed immediately. Based on the hypothesis that juvenile grunts functioned as a contact call, Campbell (1973) predicted that rates Of vocalization by a pod would increase after sunset when visual cues became useless. This was partly true for A. misstsstpptensts; VAH did remain elevated for at least one hour after sunset. Thereafter, vocali- zations declined along with feeding and other movements by the pod, and the return to cover prior to sunrise took place with little grunting by moving juveniles. Vocalizations may serve to limit evening dispersal in so far as feeding juveniles may attempt to remain in audible range of other juveniles. However, studies of orientation and homing in juvenile A. misstsstppiensis indicate that celestial cues may also be used to return successfully (P. Murphy, 1978; G. Rodda, unpublished data). Contexts in which juvenile 4. misstssipptensts grunted were discussed briefly by Herzog (1974). His observations and mine are in agreement with respect to the association of movement with grunting fn all contexts, and support the nypothesis that grunting promotes pod cohesion by acting as a contact cal}. My observations of hatchlings separated from a pod suggest that vocalizations alone provide sufficient information for accurate relocation of the main group. The increase in calling observed in isolated alligators have also been observed in gallinaceous birds isolated from their mates (Potash, 1975). The broad range of frequencies used may facilitate location of the caller in the jou dense!ly-vegetated habitats often occupied. In addition to serving as a contact call, the juveniie grunt also seems to alert other hatchlings tc unusual or new Stimuli, without conveying any information about their nature. Campbell! (1973), Herzog i05 (1974) and | have all observed grunting during feeding; it appears that these calls might stimulate other juveniles to forage as well. Movements (including arrivals and departures) of the female stimulate grunting, and hatchlings are attracted to the female's location by the grunting of other juveniles near her if she is invisible to them. The female's continued presence thus also insures group cohesion. MclIllhenny (1935) reports a female A. mMisstsstpptensts calling young to her from the nest, and H. Hunt (unpublished data) has regularly observed deep grunts (Garrick et al., 1978) used by female alligators to attract their pods. Similar behavior has been reported at hatching in Catman crocodilus (Alvarez del Toro, 1969). 1 never heard deep grunting by female A. misstsstppiensts in attendance with their pods; it may be that the deep grunt is frequently used only when pods are being transported or attracted to a new location. My observations of the juvenile distress call Support Campbell] (1973), who has suggested that this call serves only an alerting function and does not necessarily communicate alarm to other juveniles (see Chapter \). Hatchlings and other juveniles are consistently attracted to the calls of captive sidlings; in my experience juveniles appear frightened and seek cover only if alarming visual stimuli (¢.2., close approach by large objects such as humans or boats) are also present when distress calls are given. > The group behaviors of hatchling Iguana tguana show interesting similarities to those of young 4. mLsstsstpptensts. Hatchling iguanas c “> @ 3 ct emerge from nest holes in groups, and hatchlings from several diffe holes have been observed to emerge simultaneously (Burghardt et Gh 5 106 1977). Young iguanas remain in small groups after leaving the nest, and show some social attraction in selecting common basking and sleeping sites. Visual cues appear to be the mechanism by which contact is maintained, and the conspicuous dark eyespot of young iguanas has been likened to the contact calls of vocal species (Burghardt, 1977). The increased predator detection resulting from these groups is probably their principal adaptive value (Greene et at., 1978). The frequency and duration of parental care in Florida 4. misstestpptensts are both much greater than has been stated by some authors (Neill, 1971); my observations basically support Mcllhenny's (1935) generalizations. The duration of pod defens through June of the year after hatching indicates that at least some female 4. all year. This suggests one explanation for the restricted movements of adult female A. mtsstssipptensts when compared with movements of males (Joanen and McNease, 1970, 1972a; Goodwin, 1977). The dispersal of pods beginning in June may be related to the initiation of nesting by females at this time. Some females devote considerable time to mest construction and during incubation may seldom leave the nest site (Carr, 1976; Deitz and Hines, in press). Parental care of the Previous year's young must certainly be reduced once these activitias nave begun. The restricted dispersal of young 4. misstsstpptensts during their First summer could permit them to receive some maternal care, althougn its extent is probably limited by the female's preoccupation with nesting. Juveniles presumed to be 2 years oid have been observed with 107 females during droughts (Fogarty, 1974; Chabreck, 1965), and similar associations are reported for Catman crocodilus (Staton and Dixon, 1977). Juvenile A. misstesipptensis greater than 1 m TL were rarely observed near hatchlings and in view of their evident attraction to juvenile grunts and persistent references to cannibalism in the croco- dilian literature, it seems possible that they are actively excluded by protective females. A 1.2m alligator was seen to enter an enclosure containing hatchlings and eat one (D. Crider, pers. communication), and | saw an adult female threaten and chase a subadult during her response to playbacks of juvenile grunts (see Chapter V). Hunt (1978) has several observations of the exclusion of captive juvenile Crocody Lus morelett from groups of hatchlings by the parent female. The sequence of defensive behaviors used by females with their pods includes several postures which are also used in intraspecific agonistic encounters: the inflated posture, the head-emergent tail- arched posture and the bellow-grow! posture (Garrick et al., 1978). The graded series of threats which | observed in pod defense is similar to that which Kushlan and Kushlan (in press) and | have observed in females defending their nests. In both pod and nest defense, females followed initial approaches with oOpen-mouth threat postures, hissing, and open-mouth lunges. | did not pursue the pod defense sequence ct beyond open-mouth lunges and subsequent pursuit by the female, bu Kusnian and Kushian (in press) have shown that females wil] deliver mock bites'' before actually biting dummy nest intruders. in view of the similarities, the same may occur curing pod defense. One important difference in the two series of behaviors is the orientation of the 108 female. Alligators defending nests are clearly oriented to the nest; they move directly toward it when approached and often display while lying across it (Kushlan and Kushlan, in press; personal observations). Female alligators responding to my approach of their pods initially . moved toward the pod (this may have been a response to the vocalizations of the young), but thereafter directed all threats toward me. While defensive female A. misstsstpptensts approached me prior to any reaction by their young, distress calls by juveniles augmented the intensity and persistence of female threats; Mcllhenny (1935) and Kushlan (1973) have made similar observations. The fact that some females appeared only after hatchlings began to emit distress calls Suggests that this call may convey alarm to adults, or at least alert them of novel stimuli. H. Hunt (unpublished data) has observed a blind female A. misstsstpptensis which nested successfully and cared for her young by responding vigorously to their calls. Female 4. mtsstsstpptensts which protect their young against humans presumably protect them against other predators. | did not observe any instances of this, although the defensive female at the Carr property has been observed to drive away Great Blue Herons, Ardea herodtas, which attempted to eat hatchlings (A. Carr, pers. communication). Defensive behavior by nesting female A. misstssiroiensis significantly reduces nest predation (Metzen, 1977; Deitz and Hines, in press), and one would therefore expect defensive behavior to be negatively correlated with pod mortality. It was not. This could be attributed to smal] sample sizes, but a more important failure in this study involved my inability to observe many females with their pods. These pods were Y y 8) p 109 classified as minimal care pods, but they clearly had an adult alligator in attendance at least part of the time, and may have received sub- stantial protection against predators. Female A. mtsstsstpptensts which did not defend their nests against humans did nevertheless visit and maintain them, and one nesting female which had never threatened humans was observed to drive off a raccoon, Procyon Lotor (a known nest predator--Deitz and Hines, in press). Learned avoidance of humans may not necessarily disrupt all reproductive and parental activities of alligators, even though the parental care of alligators in areas with high human activity was probably somewhat reduced. Both Reese (1915) and Mc!lhenny (1935) believed that human disturbance affected the protective behavior of female A, misstsstppiensts. The behavior of other juvenile crocodilians has not been wel l- Studied, although scattered accounts suggest that it may be similar to that of A. mtsstsstpptensts. The young of all crocodilians vocalize (Neill, 1971: Campbell, 1973; Herzog and Burghardt, 1977). Pods which are defended by a parent are known to occur in Crocodylus ntlotteus (Cott, 1961, 1971; Modha, 1967), Crecodylus palustris (Dharmakumarsinhji, 1947), Croeodylus acutus (Alvarez del Toro, 1974), rocodylus morelet? (Alvarez del Toro, 1974) and Catman erocodtlus (Staton and Dixon, 1977). Medem (1971) indicates that female Melanosuchus niger and Paleosuchus valpebrosus both defend nests, but that only the young of MW, niger are gregarious and are defended. Little information js available beyond the fact that pods occur and are defended. Both Cott (1971) and Modha (1967) have observed hatchling Croeodylus niloticus basking on the head and back of adults; Modha (1967) also reports increased vocalizations by groups in response to the arrival of the mother. Cott 110 (1961) indicates that juvenile C. niloticus are extremely cryptic by day and are presumably hiding in dense vegetation. Lang (1975b) reports that hatchling Crocodylus aeutus in Florida remain under cover’ by day and emerge at night, and Webb et al. (1977) have described tidal influences on the behavior of hatchling Crocodylus porosus, an estuarine species. Flight and cover-seeking behaviors are reported in response to vocalizations of other hatchlings in wild Crocodylus ntlotteus (Pooley and Gans, 1976), and Caiman erocodilus (Campbell, 1973). Response to vocalizations and care of the young by adult males has been observed in captive Crocodylus niloticus (Pooley, 1977), Crocodylus morelett (Hunt, 1975) and Catman crocodilus (Alvarez del Toro, 1969, 1974). In the wild, males do not seem to be involved in Parental care in Crocodyius ntlotteus (Cott, 1961, 1971; Modha, 1967) or Caiman erocodilus (Staton and Dixon, 1977). While males are evidently capable of caring for young in these species, their normal contribution to parental care may be negligible. Webb et al. (1977) present evidence suggesting that the movements of Crocodylus porosus are similar to A, misstsstpptensts, in that adult females may have restricted home ranges near breeding areas while males travel extensively (Webb and Messel, 1978). Such differences in movement patterns would imply that most, if not all, parental care is likely to be maternal. Duration of parental! care is likewise uncertain for most species of crocodilians. Cott (1961) has observed maternal! defense 81 days + after hatching in Crocodylus ntlotieus, with other observations of shorter duration, and defense has been observed 5 weeks after hatching in Crocodylus acutus by Alvarez del Toro (1974). Attendance of the pod without active cefense occurs for at least 4 months in some female 111 Catman erocodilus (Staton and Dixon, 1977) and at least 2 months in some Crocodylus porosus (Webb et al., 1977). All of these studies also suggest that there is considerable individual variation in the duration and expression of parental care. CHAPTER V EXPERIMENTAL ANALYSIS OF THE VOCALIZATICNS OF JUVENILE ALLIGATORS Introduction The vocalizations of crocodilians have long been known to scientists; some of the oldest accounts include references to bellowing or roaring by adults as well as grunting or chirping by the young (see reviews by Cott, 1961, 1971, and Neill, 1971). Three main functions have been attributed to these juvenile vocalizations: attraction of the parent at hatching time to release the young from the nest, attraction of the Darent or other adults for aid in distress contexts, and attraction of siblings and other juveniles to maintain group cohesion. Data at present available (many of them from captive studies) have supported some or al] of these speculations for 1] of the 2] extant crocodilian species, and it is probable that parental care is elicited in these contexts by vocalizations of all 21 species (see Chapter iV). Lee (1968) has suggested that vocalizations of Alligator misstssipptensts might help synchronize developmental rates late in the incubation pericd and thus insure a synchroncus hatch. Data from his single experimental test support his hypothesis, but the experiment has never been repeated (Lee, 1968). The possibility that juvenile vocalizations might function arm calls within sibling aggregations has also been discussed 113 Few experimenters have examined further the function of juvenile vocalization. Playbacks of recordings of conspecific juvenile grunts were used successfully to stimulate nest opening by captive female Crocodylus morelett (Hunt, 1975) and C. ntlotteus under semi-natural conditions (Pooley, 1977). Both of these investigations also reported approaches to piaybacks of juvenile grunts by adults of both sexes; additional parental behaviors were then elicited by the presentation of eggs and/or hatchlings (Hunt, 1975; Pooley, 1977). Captive adult C. palustris attacked keepers when tape recordings of juvenile calls were played (Whitaker, 1974). Captive adult and subadult 4. misstsstpptensts also approached playbacks of hatchling calls (Herzog, 1974). Campbel! (1973) reported that captive juvenile 4. misstsstppiensts vocalized and approached the speaker in response to playbacks of their calls (and a variety of other sounds also), but in similar experiments with 4. misstsstpptensts Herzog (1974) found no consistent response. Groups of hatchling C. ntZoetteus vocalized and moved toward playbacks of their calls conducted by Pooley (1977). Observations of parental defense of young 4. mLsstsstpptensis by MclThenny (1935), Kushlan (1973) and me (Chapter 1V) all indicated that vocalizations by the juveniles were important in provoking approaches and other protective behaviors by adults. My major objectives in con- ducting playbacks to adult alligators were to characterize more completely the responses of adult and subaduit alligators of both sexes to juvenile vocalizations, and to test the hypothesis that juvenile vocalizations alone were sufficient to elicit protective behavior by parent females. Juveniles observed during the study vocalized in a variety of contexts (Chapter IV); my main purpose in conducting both field and tank play- backs to pods of hatchlings and other juveniles was to characterize group and individual responses to vocalizations in the absence of other specific stimuli. Field observations of the grunts of juvenile A. mtsstsstyptensis and their use in natural settings supported Campbell's (1973) contention that the juvenile distress call was distinguishabie from some other juvenile grunts only by the context in which the calls were given (see Chapter IV). However, juvenile A. misstsstpptensts did vocalize more rapidly when alarmed (¢.2., the repetition rate for grunts given by one individual increased). It therefore seemed reasonable to test the hypothesis that this increased rate of vocalization might indicate a distress context by conducting playbacks of grunts with different repetition rates.’ Methods Field Playback Experiments Tape loops of hatchling and yearling calls were made from calls recorded in an acoustically insulated room using an AKG 451E microphone and Nagra i!l or Tanberg Model 11 tape recorders at a tape speed of 9.5 cm/sec. Tape loop 1 was prepared from the ''distress'' calls of a hand-held hatchling alligator (SVL 12 cm) and loop 2 was prepared in an identical fashion from calls of a 26.5 cm (SVL) juvenile. in order to examine the effects of call rate on behavior, loop | (repetition rate approximately 1 cali/sec) was used to produce loop 3 (repetition rate 0.25 calls/sec). Several hatchlings calling together were used to produce a recording of multiple vocalizations (joop 4). On the basis of spectral qualities and context (the alligators were forcibly restrained and sometimes pinched to induce calling), all of these recordings fit definitions of "distress' calls by Neill (1971) and Burghardt and Herzog (1977). The recorded calls of an adult male Rana grylto used as a control were obtained from Master 13b, Bioacoustic Archive, Florida State Museum. Equipment for most playbacks consisted of one 8-inch acoustic Suspension speaker connected with a 10 m extension cord to a Roberts 6000 stereo tape recorder. The output of this system in d8 SPL for different tape loops at the playback volume settings used was calibrated using a 2.5 cm B & K condenser microphone placed 200 cm from the speaker in an acoustically insulated room (Insect Attractants Laboratory, USDA, Gainesville, FL) and connected to a B & K 2608 measuring amplifier. Amplitudes of the distress calls of two hatchling alligators also measured in this fashion ranged from 50 to 64 dB SPL; most field playbacks were conducted at 58-59 dB SPL at 200 cm. The volume of Field playbacks conducted with other systems was not measured, but was set at levels ! regarded as normal. Field playbacks were conducted in a variety of situations. Speaker placement was at water jevel on a Float, on land adjacent to water, or in the bow cf a boat. 1 remained as far from the speaker as was practical for observing responding alligators with binoculars. Many playbacks to adults were made efter the alligator had already 116 been sighted (usually basking); such alligators were almost certainly aware of my presence. In other instances, particularly playbacks to juveniles, natural cover was used effectively for concealment, and alligators in these situations were probably unaware of my presence. Some playbacks were conducted with a juvenile alligator tethered near the speaker with a light string around one hind foot. The tether permitted the juvenile to assume normal postures, but forced it to re- main. within 150 cm of the speaker. Playbacks were presented for at least 5 minutes. A positive response was scored if an alligator moved steadily toward the speaker for at least two body lengths. Negative responses were scored if movement was directed sideways or away from the speaker. For animals initially visible, response latency was the time from start of the playback to the beginning of a directed movement. Response latency for other alligators was the time from the start of the playback to the time of their appearance; thus, mean response latencies calculated were biased in favor of larger latencies. Tank Experiments Controlied experiments on the response of juvenile alligators ts recorded calls were carried out in 1977 at the Savannah River Ecology Laboratory in Aiken, South Carolina, using the apparatus described by P. Murphy (1978). This consisted of a circular tank (swimming pool) 305 cm in diameter and 91 cm high, filled to within 20 cm of the top. Opaque, uniformly dark-colored cloth screens were placed around the perimeter of the tank, and observations made through slits in the screens. 117 This left celestial cues and irregularities in the screen and tank as the only visual cues availabie to experimental alligators. The play- back apparatus consisted of two 8-inch acoustic suspension speakers connected to a Roberts 6000 stereo tape recorder. The speakers were placed in 180° opposition just outside the screen, either NS-SE or NE-SW. Air temperatures at the time of testing were 26°C-33.5°C during the day and 25°C-27°C at night. These temperature ranges corresponded to those measured when juveniles were active in the field. All tests were run under clear, moonless skies. Tests were conducted both day and night. Alligators were intro- duced into the tank from the sides of the pool; different release points were used for each trial. A release device located in the center of the tank was used during preliminary trials, but abandoned because it appeared to interfere with the response of alligators to the playbacks. Following introduction, the test alligator was allowed two minutes to acclimate to the tank. After two minutes, the speaker farthest from the alligator, designated speaker A, was turned on. An ''A'' response was recorded if the alligator moved to the wall adjacent to speaker A (within 50 cm of the wall for hatchlings, 100 cm for yearlings). Once an A response was obtained, the other speaker (B) was turned on and speaker A was turned off. !f the alligator then moved to speaker 8, a ''B'' response was recorded and the experiment was terminated; other- wise speaker B or speaker A (depending on the response of the alligator) ling calls and loop 2 for yearling calls. Results Field Playback Experiments a SYP SCR Experiments: Almost all subadult and adult Alligator misstsstpptensts of both sexes responded positively to playbacks of loop 1, the juvenile grunt (Table 5-1). Response latencies could not be determined for some responding alligators which were able to approach the speaker unseen and whose presence was then belatedly noted. The slightly lower percentage of positive male responses versus positive female responses was not statistically significant and was possibly due to the fact that | was visible to all three non-responding males. However, there were other consistent sexual differences in response to playbacks of loop 1. Female response latencies were signifi- cantly lower than those of males (p < .05, t-test); although problems with visibility make these latency data somewhat suspect, males never exhibited the immediate orientation to the speaker that | observed with most females. In 1? of 12 instances, responding females assumed the inflated posture (Chapter IV) while swimming toward the speaker and/or while motionless during the playbacks; only 2 of 7 males used this inflated posture when responding to playbacks (difference significant, 5 | p = .01, Fisher exact probability test). All alligators returned to a norma! floating posture after playbacks ceased. They usually remained motionless for a few minutes, then swam back in the direction from which they had come. On two occasions | re-started the playback after alligators had begun to swim away; both alligators (adult females) returned to the inflated posture immediately and oriented toward the Table 5-1. Responses of adult and subadult American alligators to playbacks of the juvenile distress call. No. of Maximum Response Alligators No. of No. of Positive _Latency (min) Tested Animals Trials Resoonses X + s.d. (range) Ena ee ee ee eae rae eng Ad. 2 8 10 7 6.0 (4.0-9.3) n = 3 Ad. 2 7 iz 12 12 @ Isl (il=3.5} wn = 9 Unk. Ad. 5 5 5 9.0 + 6.2 (2-16) n=4 Subadult 5 5 5 0.7 * 1.3 (143) n= 5 Total 25 32 29 (91%) 120 speaker. Females also came closer to the speaker before stopping than males, although this was not statistically significant; 7 of 12 females stopped 2 mor less from the speaker, while only 2 of 7 males approached this closely. On one occasion in which a truck was used as a blind and the speaker placed next to it on a levee, a male and female alligator both emerged from an adjacent canal and climbed up the levee in response to a playback. Three of the above playbacks of loop | to females were aia with a juvenile alligator tethered next to the speaker. The first of these was conducted on 15 May 1977 at the Carr pond to a female which had nested successfully the previous year. The speaker was placed on Floating water weeds (mostly Hydrocotyle wmbellata) approximately 3 m from the north shore of the pond, and the juvenile (TL 35 cm) tethered to adjacent vegetation. | observed from bushes approximately 15 m to the northwest of the speaker; all locations (letters) in the following account from my field notes refer to Fig. 5-1. 1632 - Playback begun. 1533 - Adult female alligator (total length approximately 2.6 m) observed at A (Fig. 5-1) swimming toward the speaker in an inflated posture. Immediately after becoming visible, the female turned toward a 1.2 m subadult alligator (not previously observed) at B and swam rapidly toward this juvenile, chasing it into the marsh to the southwest. The female (still in the infalted posture) stopped at 8 for approximateiy 15 sec. (open water) 12] Resconse of an adult female alligator at the Carr property to playbacks of juvenile grunts and to a natchling alligater tethered near the speaker. Letters refer to locations described in the text. 122 1637 - Female resumed swimming toward speaker. 1640 - The female arrived at C. She had maintained the inflated posture for the entire trip, but deflated as she arrived and paused briefly. The female then pushed her head into the weeds toward the speaker, and at this time the tethered juvenile began to grunt rapidly. 1641 - The female submerged her head with a quick downward and slightly backward movement, and immediately surfaced it. 1641:45 - The head submergence was repeated, and the juvenile ceased grunting. 1642:45 - The female pushed her head forward (north) into the weeds next to the juvenile and again briefiy submerged her head. 1643 - The female bit quickly to the side into the weeds by the juvenile, then pulled her head back and submerged completely. She surfaced at D, still facing the speaker, and assumed the inflated posture; masses of weeds were sticking out of both sides of her mouth. 1643:45 - The female shook her head from side to side once and deflated. 1645 - The female moved her head slightly, and the previously tethered juvenile became visible next to her snout. She had apparently carried the juvenile (along with adjacent plants) from the speaker to D in her mouth. 1646 - The juvenile began swimming slowly toward the speaker. 1647:30 - Playback was turned off. The juvenile was approximately 1.5 m from the female's snout. 1648 - The female turned and began swimming south. The juvenile was still tethered to the vegetation stuck in the female's jaws and was pulled underwater backwards as the female moved. The juvenile vocalized as it submerged, and the female then stopped swimming. 1650 - The juvenile surfaced next to the female's head. A second smaller alligator (size consistent with 1976 hatchlings) was observed at H, oriented toward the female. For the next 20 minutes, the female alternated short (5 mor less) move- ments to the south in a normal swimming posture with return movements toward the speaker (which was turne off) in the inflated posture. These returns were initially associated with the grunts of the juvenile as it was pulled under by the tether stuck in her jaws, but continued in the absence of any discernable stimuli after the female released the remaining weeds from her jaws at 1703. Once released, the juvenile continued to orient to the female's head. It crawled up on her neck twice and on the second occasion actually rode there as the female moved about 2 m. A playback with a tethered juvenile alligator was repeated with the Carr female on 4 June 1977. This female had begun nest construction and approached from the vicinity of her nest site in response to the playback. The tethered juvenile on this occasion did not vocalize or move after the female's arrival at the speaker, and it may have been invisible to her in the weeds. The female remained near the speaker for > minutes before swimming into the marsh near her nest. Three other playbacks of joop 1 with tethered Juveniles were attempted on Orange Lake In areas previously known to contain females 124 with young (sighted in the area within 2 weeks of the playback). None produced a response. However, no adult alligators were sighted in the playback areas on the dates of the playbacks; consequently no conclusions could be drawn from these failures. At 1430 on 15 September 1977 a playback of loop 1 with a tethered hatchling (TL 28 cm) nearby was presented to an adult female alligator (TL approximately 2.4 m) on Biven's Arm. This female had nested success- Fully in 1977 and had previously defended her nest and pod against humans (D. Jackson, personal communication). The female responded immediately to the playback by moving up to the speaker with her head near the hatchling, and appeared to orient alternately over the next 10 minutes between the speaker, the tethered hatchling, hatchlings from her pod which had followed her and were also vocalizing, and my move- ments as |! attempted to film her behavior. Approximately 10 minutes after the start of the playback one of her head movements brought her eye next to the tethered hatchling, which was grunting rapidly at this time. In one continuous movement the female swung her head toward the natcnling, tilting her snout down slightly as she did so, opened her mouth and closed it around the tethered hatchling. She remained in this position for approximately 10 seconds, then opened her mouth and released the hatchling as she backed away about 60 cm. These movements were not sufficient to pull the hatchling off its tether: it continued to struggle and call occasionally after being released. By this time at least 7 other hatchlings from the pod had followed the female and approached to within 2 m of her. One of these hatchlings climbed on the female's snout while she was facing the tethered hatchling and the 125 speaker (which was turned off). The female responded by lifting the tip of her snout out of the water and then tilting her snout (by rotating her head around its long axis) approximately 20 degrees to the left; the hatchling slid off after the third tilt. This was the only occasion on which | observed a hatchling shaken off a parent female's head or body. The female and her pod remained by the speaker and the tethered hatchling until after sunset (2200). 1! removed the tethered hatchling on the next day; it was uninjured. The responses of groups of hatchlings to field playbacks of loop | were quite variable; the proportion of individuals in a ped responding to a playback ranged from 0 to 100%, making generalizations difficult. The ''typical'' response of individuals in a pod was bimodal: there was an initial positive response and approach to the speaker, followed by a pause and then a steady movement away from or oblique to the speaker into vegetation. For 10 pods, a mean of 31.0 + 31.0% of the hatchlings visible responded positively to the playback; this was significantly more than the 11.9 + 16.8% which initially responded negatively (p < .01, Chi-square test). Playbacks of Rana gryltico calls presented in identical fashion to 3 groups of hatchlings and 2 individual one-year old aliigators produced no reaction. Many positively-responding natchlings emerged from cover where they had not been visible prior to the start of a playback. The average increase in number of hatchlings visible during the playback was 40.7 + 7. 3% (range 0-150%) for 9 playbacks, and this increase was significant (p < .01, t-test for paired samples). However, by the conclusion of the playback the mean increase in number of juveniles visible was an insignificant 2.5 + 42.9% (range -100 to +57%); this was 126 a reflection of the movement into cover by many animals which had initially responded positively. There was also a slight, non-significant increase in the proportion of the pod in the water for 5 playbacks. Hatchlings moving toward the speaker or cover grunted, as was customary for moving animals. Other pod members occasionally grunted in response to the Speaker; these grunts appeared similar to those of group members in response to the grunts of solitary juveniles. The group as a whole did not appear to vocalize more during playbacks, and VAH's calculated for two playbacks were within normal ranges. One-year old juvenile alligators responded similarly to loop 1 playbacks. Positive responses were obtained From 3 yearlings in one playback to a pod of at least 7 one-year olds, but 2 of these 3 then moved under cover after approaching the speaker. The third yearling had initially approached the speaker and paused. It then turned 90 degrees to its right and began swimming rapidly towards an adult alligator (TL 2.4 m) which was approaching the speaker in the inflated posture from about 15 m away. The yearling entered a clump of vege- tation directly in the path of the adult and was lost from view. Five of 7 individual yearlings observed with pods of hatch!ings responded positively to playbacks of loop 1. Three playbacks of loop 2 also produced bimodal responses from juvenile alligators. Positive responses were recorded from 5 to 8 hatchlings (68%), 6 of 8 yearlings (75%) and 2 of 2 subadults (summary of 3 playbacks); five of these yearlings and both subadults subsequent ly moved away into cover after this initial positive orientation. All three of these playbacks were conducted in locations where adult females were believed to be present, but no adults were seen. One 2.1 m adult of unknown sex approached a playback of loop 2 in a normal swimming posture before it also turned and moved away. Three additional field experiments were conducted in which playbacks with different call rates were presented successively to the same pod of hatchlings (Table 5-2). Loop 3 (which was created by spacing out the calls on loop 1) produced no response. Playbacks of loop 1 produced responses typical of other playbacks of this loop (see above): there was an initial positive response by several hatch- lings (none of which had responded to loop 3), an increased number of animals became visible and finally there was a general movement away from the speaker into cover. The responses of 2 pods to loop 4 were similar to those produced by loop 1, but more animals became visible and more responded positively during loop 4 playbacks (Table 5-2). Qualitative differences in the responses to loop 4 were especially striking. The response latency for all animals that responded positively was virtually 0, and most animals grunted. Hatchlings swam toward the speaker rapidly, and when stationary lifted their heads high out of the water while craning their necks up and forward, as though looking for the source of the commotion. Occasional head-lifting was observed during leop | play- backs, but not to this extent. Most hatchlings responding positively to loop 4 playbacks paused for 1.5-2 minutes after their initial approach, then turned away and swam slowly back under cover; they did not appear alarmed. An adult alligator emerged from shoreline vegetation near the pod during one playback of jioop 4 and stopped, facing the speaker with head only emergent. This was the only occasion that an adult was observed with this pod. 128 (%0S) § Ol 9 (262) Z 6 if 0 ) 9 £ (409) 9 Ol Ol 0 6 6 z (%98) 9 l S 0 S S l S2y SOg “ON bulang 7412815 SOY SOg “ON burang SOY SOd “ON Burang 4845 ~ pog PLGISIA s4equny PIGISIA s9quiny PIGISIA sequin "Des/S[[e0 G < “Das/,{peo | “DJ9S/S{[e2 Gz7°o doo | doo q € doo7 "saqes UO}11}Ade4 YUB4945 Ip YIM squn46 apruaanf 07 s4uojzebiyye Buljyoaey yo spod yo sasuodsoy "Z-G apqey Tank Experiments When tested individually in the arena at the Savannah River Plant, most hatchling A. misstsstppiensts oriented and moved to playbacks of hatchling distress calls presented at | call/sec (Table 5-3). Eight of the Il hatchlings responding reversed an initial directional response in order to approach the playback (B response). Four of these animals grunted during responses, and two of these attempted to climb over the wall of the pool closest to the speaker. Controls were tested in silence (natural sounds available around the outdoor arena); these alligators swam slowly around the arena generally close to the wall of the pool, with frequent pauses and no preferences for a particular direction. Two controls vocalized. During the initial 2 minute acclimation period, the behavior of hatchlings which demonstrated A or B responses during testing was identical to that of controls. Nine one-year old alligators were also tested in the arena using playbacks of yearling distress calls (loop 2). Results were similar to those obtained in hatchling tests: five yearlings produced B responses and the remaining 4 gave A responses. Five of these yearlings vocalized during testing. Only two controls were run; both of these animals remained largely motionless for most of the test period and did not vocalize. Discussion The results of field playbacks clearly indicate that juvenile vocalizations alone are sufficient to elicit some interspecific agonistic displays (inflated posture) and to provoke approaches by adult 4. 130 Table 5-3. Response of hatchling alligators in an artificial enclosure to playbacks of juvenile grunts at 1 call/ sec. All control animals swam slowly around the edge of the tank, pausing frequently. Experimental Control] Response Number No Number Tested A 8B Response Tested Response Day ) z & 3 6 Circled arena slowly Night 7 l 4 2 7 Circled arena slowly Total 16 3.6COUB 5 13 13] misstsstopiensts of both sexes. The differences in responsiveness between males and females further indicate that males are not principally involved in parental care in A. misstsstpptensts, although the possibility that males might be protective in some situations remains. The responses of females to tethered hatchlingsraise intriguing possibilities. Mouth transport of a juvenile in May, 8 months after the hatching season, clearly indicates that this is a well-developed protective response which is not necessarily restricted to hatching. It provides additional evidence that parental care in A. mtsstsstpptensts includes active protection of young up through the following nesting season. While protective females correctly oriented to playbacks and approached to within | m of tethered hatchlings, it appears that visual stimuli might also be necessary to induce mouth transport. Both females in which this was observed picked up juveniles only when these juveniles were visibly active near the speaker. Hatchlings which | released near protective females in attempts to duplicate Kushlan's (1973) observations all swam or crawled away normally and were ignored. The observation at Biven's Arm is particularly noteworthy, since the female in this instance chose to mouth the tethered hatchling, which was struggling, in preference to other young from her pod which were vocalizing nearby but swimming normally. The curious head submergences which the Carr female exhibited when next to the tethered hatchling have not been previously reported. They might have been associated with vocalizations, but if so these were inaudible to me 15 m away. The purpose of the head movements might be to signify presence of the adult to the juvenile. 132 An extremely active protective role for some female A. missts- stpptensts is suggested by my observations of mouth transport and those of Kushlan (1973). The female at the Carr property swam across the pond and probably left the remainder of her pod in response to a playback. In another trial, two adult alligators on Payne's Prairie climbed out of the water and up on to a levee, and J. Kushlan, M. Kushlan, and | (unpub. observations) have observed a female 4. misstsstpptensts in the Everglades emerge from a canal and approach a truck where some of her hatchlings were being tagged. Positive responses to playbacks conducted while | was concealed from view were exhibited by 4 aduit alligators (believed to be females) apparently associated with peds with which | had never seen an adult. These results further support the hypothesis (advanced in Chapter IV) that human presence may inhibit the behavior of females which are otherwise protective of their young. The positive responses of subadult and adult male alligators to juvenile calls can be interpreted as weak evidence for protective be- havior, genera! curiosity or investigation of cures which might potentially lead to food. Adult bullfrogs, Rana catesbetana, are attracted to the distress calls of immature frogs and evidently make feeding attempts on the immatures and/or their predators upon arriva} (A. Smith, 1976). Cannibalism has deen documented in A. misstsstpptensts (Kellogg, 1929; Perkins, 1955), but evidence from large scale food Studies indicates that it is extremely rare. Three analyses of the stomach contents of alligators 91 cm (3 feet) or larger from Louisiana report a total of only 5 of 935 stomachs (0.5%) containing alligator parts (Giles and Childs, 1949; Valentine et aZ., 1972; Joanen and McNease, 1977); predators of juvenile alligators were much more frequent in stomach contents. Modha (1967) has reported positive responses by adult Crococylus niloticus (presumably of both sexes) to playbacks of juvenile calls; both cannibalism and protective behavior by adult males have been documented in this species (Cott, 1961; Pooley, 1977). The responses of hatchling and one-year old alligators to playbacks of loop | are consistent with the hypothesis that high-intensity juvenile grunts (= distress calls) alert and stimulate movement by young alligators, but do not communicate alarm. Reasons for the bimodal] response are not clear to me. In some cases, juveniles may have detectec my presence after their initial approach and responded by moving under cover. However, this is not likely for instances in which | was well-concealed and observed identical responses. In responding to juvenile grunts, juvenile alligators may simply be alert for meaningful visual stimuli--¢.e., the approach or presence of the parent female, other juveniles, potential prey or potential predators. Subsequent behavior may depend on what is encountered. 1{f there are no visible stimuli associated with grunting (as was probably the case Tor most playbacks), then the probability that the vocalizing individual is separated from the pod and/or being eaten may increase. Since these are undesirable situations, cover seeking by the remaining pod members would be adaptive. If this is true then juvenile grunts would communicate distress to other juveniles only if persistent. In addition to their initiaily positive responses to playbacks of distress calls, juveniles Clearly are attracted to calls of juveniles which have been captured and are unequivocally in distress. 134 The probable explanation for this must be the likelihood that the parent female will also respond (Table 5-1). Juveniles moving toward the source of vocalizations would therefore be reducing their separation from the parent. Presumably, proximity to the adult female offsets any increased risks of predation incurred in moving toward locations where predators are potentially present. Adult alligators are known to consume virtually all known predators of hatchlings (Mcllhenny, 1934, Valentine et al., 1972; Joanen and McNease, 1977). Hatchlings which fail to respond to vocalizations may also risk separation from the pod; the disadvantages of this (in terms of increased probability of future predation) may be greater than the potential disadvantages of a positive response. The results of my limited trials using different rates of grunt- ing suggest that the extent to which juveniles are-initialiy alerted by grunts depends on the repetition rate rather than the frequency spectrum of these grunts. Amplitudes and frequencies of the calis were identical for all trials, but it remains possible that the increased response to loop 4 was a response to the increased number of calling individuals eon this recording. If so, this would imply that juveniles could successfully distinguish the grunts of different individuals on the basis of siight differences in frequency. Garrick and Garrick (1978) have found that the repetition rate of grunts of distressed Catman erecodtius is relatively stable (within broad ranges) between 18 and 33°C. Ten minutes after emergerice into morning sunlight, basking alligators could have body temperatures 5°C higher than juveniles remaining in the water, and differences between adults and juveniles 135 in some situations could be even greater (E. Smith, 1976; Smith and Adams, 1978). I repetition rate of grunting conveys information, then it is important that the rate-temperature relationship observed in C. erocodilus be valid for A. mississtpptenste as well, in order to reduce signal ambiguity (Garrick and Garrick, 1978). Arena playbacks provided additional evidence that calls given in distress contexts did not necessarily convey alarm when played back in other contexts. The hypothesis that grunts of juvenile A. mtsstsstp- piensts function as contact calls was also supported by the resuits of the arena tests, although these were poorly controlled. Juveniie alligators had no difficulty in locating the source of the sounds, and in individuals which gave B responses, only momentary confusion was produced by switching speakers. When tested in the same arena in the absence of auditory cues, juveniie alligators used celestial cues to demonstrate a significant preference for directions normal to their home shorelines (2.9., Y-axis orientation--P. Murphy, 1978). The results from my tests indicated that individual alligators in novel situations respond to auditory cues more readily than to celestial ones. CHAPTER VI SUMMARY AND CONCLUSIONS The behaviors of juvenile Alligator misstsstpptensts are effective in actively maintaining group cohesion for at least 9 months after hatching. The most important of these behaviors is the juvenile grunt, which functions as a contact call. Grunts are given most often in situations likely to rasult in separation of individuals from the group, t.@., during or in response to movement, and during nocturnal foraging. They are used by isolated individuals to orient and return to the group, and are given in response to other stimuli of interest to alligators, such as prey, the approach of potential predators, and the approach or movements of the female. !ncreases in grunting also occur at two predictable intervals, morning and evening emergences, and follow long periods of relative silence during which pod members have become more widely separated. The social bask is particularly important in main- taining cohesion, and the reaggregation of juveniles following dispersal by an intruder fis quite similar. All of these behaviors indicate that while the presence of an adult female is an important stimulus in promoting pod cohesion and coordinating movements, pod cohesion can be effectively maintained in her absence. The use of regularly repeated signals which have continual effects on the receiver nas been referred to as tonic communication by Schleidt (1973). Tonic communication via contact calls such as those used by 136 137 alligators is also characteristic of waterfowl and gallinaceous birds when maintaining contact with mates or siblings (Collias, 1960; Stokes, 1967). Schleidt (1973) has hypothesized three main functions for tonic communication. The first is the use of calls as a beacon or homing signal, which has been documented for 4. mtssissippiensis. A second function may be that repetition insures receipt of a signal over background noise, especially if receivers can use signal averaging. This might be another way of accounting for the increase in VAH of pods of alligators after sundown; the loss of visuai contact would make the receipt of at least some vocal signals more important, particularly during a period of rapid movement. Finally, Schleidt has suggested that repetition of signals for different periods or at different rates may convey different information than individual signals; this is suggested in A. musstsstpptensts by the bimodal responses of hatchlings to playbacks. The use of juvenile grunts by predators may become a problem when rates of vocalization increase. One playback of juvenile alligator grunts on Payne's Prairie attracted a raccoon, Procyon lotor, from over 100 m away to within 20 m of the speaker. In A. mississtpptensis, a reduction in the number of grunts/series is concurrent with the rise in VAH. This might represent a partial solution to the predation problem; single grunts would provide general location information to other pod members, but would be more difficult to locate than a longer series. Qne of the major advantages ascribed to group behavior js that it results in a reduction in each individual's risk of predation. This may result from increased likelihood of predator detection (Vine, 1971), the reduced likelihood of any one group member being chosen over another 138 ("selfish herd"! hypothesis, Hamilton, 1971) and the possibility of group coordination in escape which may confuse or alarm potential predators (see Wilson, 1975, Chapter 3). 1! do not consider either of the latter two to be likely for A. misstsstpptensts. Pods of alligators scatter rather than contract when approached; their escape responses are coordinated only in the sense that juvenile grunts increase, and in any case the submergences and cover-seeking behaviors normally used suggest a cryptic strategy rather than an escape response intended to confuse or alarm. Increased predator detection is a likely result of grouping in A. mtsstsstppiensts, and since pod members are normally siblings it is also possible that kin selection has favored the use of juvenile grunts as alerm calls in distress contexts (Staton, 1978). !t is much more likely, however, that grouping in A. mtsstssipptensts is related to the large amount of parental care, including defense against predators, that pods receive. As discussed in Chapter 4, the restricted home range of adult female alligators makes it likely that even those females which are not always in attendance would potentially be close enough to their pods to respond to a juvenile in distress. The fact that juveniles first begin to disperse significantly from the den in June when nesting begins is circumstantial evidence that there may be some expectation of parental care until this time. Femate A. mtsstsstoptensts may be involved in reproductive activities including parental care virtually all year, although there is individual variation in female solicitude toward nests and young. The reproductive effort of femaie alligators begins with nest construction in June, and maintenance of the mound, including repair following 139 predation, continues through the entire incubation period for some females. Some females actively defend the nest, using a consistent ritual which includes displays also used in other intra- and interspecific agonistic encounters. Nests are opened by the female and some young are transported to the water in her mouth. Subsequent care of the young may involve regular attendance by the female up through the following year. During this period, young are led through small pools created by the female until they arrive at her den, where they overwinter. Communi- cation between parent and offspring involves a positive response by the young to the sight of the female as well as their use of distress calls to attract her; females use ocalizations to attract young to them. Active defense of pods involves ritualized threats similar to those used during nest defense; protective females may be able co distinguish young in distress from other pod members. Juveniles in distress are not Ooniy protected prior to predation, but in some instances retrieved and returned to the pod by the female. A variety of evidence from recent studies of other crocodilians suggests that the behaviors mediating pod cohesion and parental care . . . ° ensts may be widespread throughout the Crocodylidae 3 os ‘ = 3 m0) ww ct oO i ot 3 e? °. (Chapters I11, IY and V). It is significant that while no other crocodilians have been as well studied as 4. misstssipptensts, all Parental behaviors described above (including nest opening, mouth trans- port of young by acults, pod formation, attraction of adults to calls oF juveniles, and vocalizations by juveniles in response to disturbances, appreacnes of adults and during feeding) occur in at least one other crocodilian species and usualiv in members of both the Alligatorinae 140 and the Crocodylinae. Some differences, probably related to habitat, clearly occur. For example, Garrick and Lang (1977) have suggested that there may be slightly greater emphasis on vocal communication in marsh- dwelling species such as A. misstsstpptensis, while visual signals may play a greater role in crocodilians which occupy larger water bodies, such as Crocodylus niloticus. Possible differences in formation and duration of pods in crocodilians from lotic versus lentic habitats have also been discussed (Chapter lil). Nevertheless, a basic system that involves parental care of a coordinated social group of juveniles and is mediated by vocal communication is typical of the family. Sound spectrographs of juvenile grunts of all species of crocodilians studied are strikingly similar (Campbell, 1973; Herzog and Burghardt, 1977; Deitz, unpublished data). Nests opened at hatching by Caiman crocodtlue (Staton and Dixon, 1977), Crocodylus porosus, (Webb, 1977), Crocodylus movelett (Hunt, unpublished data) and A. misstssipptensis appear identical, and it has been suggested that the nest-opening responses of crocodilians may be quite stereotyped (Deitz and Hines, in press). The behavioral similarities of the Alligatorinae and the Crocodyl]inze are of considerable evolutionary significance, for they provide con- Vincing evidence that their common eusuchian ancestor, at least, possessed weli-developed systems of juvenile social behavior and parental care. The Ailigatorinae and the Crocodylinae have been distinct since the late Cretaceous (Siil, 1968); this suggests a considerably earlier origin for parental care and juvenile social groups, which inust have been fairly advanced by the time of the split. The behaviors of the extant crocodilians Tomistoma schlegelt (Tomistominae, Crocedy!idae} and Gavtalts gangeticus (Gavialidae) are almost entirely unknown; the 14) young of both species emit typical juvenile grunts (H. Campbell, pers. comm.; C. A. Ross, pers. comm.). Some additional evidence of the behavioral sophistication of the early Eusuchia is provided by the similarities in adult social signals of A. mtsstsstpptensis, Crocodylus acutus and C. ntlotteus (Garrick and Lang, 1977). The behaviors of extant Crocodilia may thus constitute better evidence for the existence of complex social behavior in Mesozoic thecodents than inferences based on dinosaur morphology (Brattstrom, 1974; Farlow and Dodson, 1975), physiology (Bakker, 1975), or fossilized tracks (Ostrom, 1972). Some conjectures concerning the origin of parental care in the Crocodilia can be made, although it is obviously impossible to do more than speculate on the origins of behaviors which are at least 65 million years old. The most reasonable guess would be that parental care of the young developed as an extension of care of the eggs. £gg-broeding appears to have evolved several] times in Recent reptiles: it occurs in several skinks, Ewmneces (Smith, 1946; Evans, 1959), in the king copra, Ophtophagus hannah (Oliver, 1956) and in Python molurus, wher it also involves metabolic changes in the brooding female (Vinegar et al., 19790). It does not seem unreasonable to postulate its existence in the earliest crocodilians or in other thecodonts. Active protection of the eggs might readily evolve in response to high nest predation; colonial nesting by Recent Crocodylus ntloticus (Cott, 1961) might represent another such response. Cott (1961!) also points out that young C. nticticus cannot escape from most hole nests unaided, and | nave found hatchling A. mtsstsstpptensis that were not removed by the carent dead in mound nests (Deitz and Hines, in press). Thus, even if active defense did not always occur, the nesting strategy of ancestral crocodilians might have required at least a return by the parent at hatching. Protection of young thecodonts after hatching would most likely also develop in response to predation. Trivers (1972) has reasoned that once a female has invested heavily in her offspring, further investments wiil be strongly selected for to protect this initial committment. If this is true, early crocodilians would have progressed readily to post-hatching care. An analysis of parental investment by Maynard-Smith (1977) suagests that even though initial investments by males are lower, male parental care is also expected in situations where predation on juveniles is severe. Data on natural mortality of young Catman erocodilus and Crocodylus morelett would be of great interest in tis regard, since substantia! parental care has been observed in captive males of these species. Protection of scattered hatchiings would be difficult and probably ineffective against most predaters. If parental protection is important to juvenile survivorship, aggregations of juveniles would also be favored, since these would be advantageous to both protective parents (which could more efficiently protect more young) and individual offspring (whose probability of being close to and protected by the parent would increase in a group). The possibility that crocodilian juvenile groups evolved in the absence of parental care is suggestec by the existence of juvenile social aggregations in Iguana tguana (Burghardt et al., 1977). However, the positive responses of juveniies to the sight and vocalizations of adults and the protective responses evoked in adults by juvenile distress calls make it more 143 plausible that the protective parent has been the major selective ad- vantage to pod formation in crocodilians. One last consideration that has received far too little discussion is the role of learning in the behavior of the Crocodilia. Learning in crocodilians has been largely neglected, despite rampant speculation on the mental capacities of dinosaurs and indications that when their physiology is taken into consideration, crocodilians learn quite rapidly (Northcutt and Heath, 1971). Throughout this study of A. mtsstssippiensts there is evidence that the behaviors of individuals are readily modified to suit different environments and conditions. Behaviors such as parental defense of young may be 65 million years old, yet individual females are able to eliminate defensive behavior in response to human disturbance without altering other parental behaviors such as nest opening or cre- ation of pools for juveniles. The ontogeny of crocodilian behavior patterns will unquestionably be difficult to study, but such studies should produce some interesting results. Crocodilians have survived and flourished as aquatic carnivores while their terrestrial relatives have become extinct. The develop- ment of mutable reproductive and juvenile social behaviors that provide for extensive parental care in a variety of environments has probably been an important factor in the evolutionary persistence of this order. 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He arrived at the University of Florida in 1973 to continue his lifelong interests in zoology. He will be married to Joan Hilarie Spiegel on June 24, 1979, WwW nh | certify that | have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. | eee eS Archie Carr, Chairman Graduate Research Professor of Zoology | certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Walter Auf fenber Professor of Zoglogy | certify that | have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Odin M hooApgceren A Jon H. Kaufmann r Professor of Zoology | certify that | have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for Doctor of Philosophy. Donald A. Dewsbury : Professor of Psychology This dissertation was submitted to the Graduate Faculty of the Department of Zoology in the College of Liberal Arts and Sciences and to the Graduate Council, and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. June, 1979 Dean, Graduate School UNIVERSITY OF FLORIDA TT 3 1262 08553 9764