UN I HARVARD UNIVERSITY Library of the Museum of Comparative Zoology MUS. COMP, ZOOU L RV OCCASIONAL PAPERS Ag8 3 ° '982 of the MUSEUM OF NATURAL HISTORY The University of Kansas Lawrence, Kansas NUMBER 103, PAGES 1-30 JULY 29, 1982 MOLTS AND PLUMAGES OF FLYING STEAMER-DUCKS ( Tachyeres patachonicus ) Philip S. Humphrey and Bradley C. Livezey1 INTRODUCTION The molts and plumages of southern South American waterfowl are very poorly known compared to those of the Northern Hemi- sphere. Weller (1968:209) noted that "fairly typical Northern Hemisphere patterns [of plumage sequence] are apparent in south- ern Cinnamon Teal and Argentine Ruddys, suggesting that these are recent arrivals to South America." Murphy (1936:941) asserted that "males of no South American duck have an eclipse plumage, which is so characteristic among northern-hemisphere species." He also indicated (1936:961, 971) that some South American species, including steamer-ducks (Tachyeres), have gradual instead of si- multaneous molt of the remiges. We began studies of the molts and plumages of steamer-ducks as part of our investigation of the systematics and ecology of the genus. The great similarity in appearance of the several species of steamer-ducks has been a source of difficulty in interpreting their taxonomic identities and geographic distributions. Some of the tax- onomic problems were resolved by Muqihy ( 1936) who determined that the widespread Flying Steamer-Duck (T. patachonicus, Fuego- Patagonia and the Falkland Islands ) , and the Falkland ( T. brachy- pterus) and Magellanic (T. pteneres) Flightless Steamer-Ducks were three distinct taxa rather than a single species, as had been believed by many authors (see review in Murphy 1936:951-972). Humphrey and Thompson (1981) described another species of flightless steamer-duck (T. leucocephalus) from the coast of Chubut 1 Museum of Natural History and Department of Systematics and Ecology, University of Kansas, Lawrence, Kansas 66045. 2 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY which, because of its great similarity in the field to other species of steamer-ducks, had been identified by other workers variously as T. patachonicus, T. pteneres, and possibly T. brachijpterus. We collected data on molts and plumages of steamer-ducks in Fuego-Patagonia during December 1980-February 1981 to attempt to determine the different sources of variation in appearance of the head and neck, i.e., taxonomic, geographic, sexual, seasonal, and developmental. This paper presents the results of our studies of the molts and plumages of Flying Steamer-Ducks. MATERIALS AND METHODS Specimens We collected 57 specimens of Flying Steamer-Ducks in Ushuaia (Tierra del Fuego), Puerto Deseado (Santa Cruz), and Puerto Melo (Chubut), Argentina, during September-November 1979 and De- cember 1980-January 1981 (Table 1; Appendices 1, 2). Each specimen was sexed by examination of gonads and the syringeal region of the trachea. We saved head pelts from 14 and skins of eight specimens collected during 10-16 October 1979 in Puerto Deseado and 5-17 November 1979 near Ushuaia. Within one to three hours after collection, the head and neck of each bird collected in 1980-81 were cleaned, dried, and photographed in color under standardized conditions with a Polaroid SX-70 camera. In addition, for most specimens from 1980-81, we examined the inside of the fresh skin and noted the distribution and abundance of new growing feathers. We obtained limited additional information on molts and plum- ages of steamer-ducks from notes, study skins, and color slides pro- vided to us by several colleagues. Although we have examined many skins of Flying Steamer-Ducks from several museums, we have not used data from them since none had associated informa- tion concerning condition of the bursa of Fabricius and very few had adequate information concerning condition of the gonads. Throughout our work we were concerned with field identifica- tion and therefore emphasized variation in aspect of the head and neck in relation to sex, age, and time of year. Estimated Age Classes We measured the gonads of all 57 specimens upon which this study is based and determined condition of the bursa of Fabricius ( and measured it when present ) for specimens collected in 1980-81 and for one collected in 1979. To facilitate interpretation of molts and plumages, we used data on size in mm- (length X width in mm) of gonads and condition and size in mm2 (length X width in mm) of the bursa, to divide STEAMER-DUCK MOLTS AND PLUMAGES CD OS oo c -O a > X 4-< 02 +J s '2 •3 cc — u 03 "O '5b CD -3 4_, -i-h rt CD CD & o 3 -o CD C r- 3 OS o 3 CD CD N O Cu CD & bo o CD a 03 '5b 3 CD .3 6 CD a DC no 3 3 CD 03 3 S "= OT a 3 -S -S o as -c -0 03 3 S5 O I Si PQ 00 CD 3 CD 0 CD c« -D 03 3 03 03 -O OS W PQ 3 pa ^h cm co 1 in cd 4 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY our specimens and associated information into five groups represent- ing three estimated age classes, described below ( Table 1 ) . 1. Juvenal birds a few weeks old. — Two juvenal males were col- lected from a family group on 20 and 22 January. They were in full juvenal plumage, approximately %-adult weight, and their growing primaries were approximately 7 and 10 cm long. The bursas of these birds were 720 and 954 mm in size and left testes 32 and 36 mm2. 2a. First-year birds approximately 10 months old. — Three speci- mens collected during September-October had very small gonads ( Table 1 ) , frayed elongate innermost secondaries lacking the silvery gray wash of the basic wing, and brownish upper wing coverts (medium bluish-gray in basic wings). On this basis we estimate that they were in their first year of life and probably approximately ten months old. 2b. First-year birds approximately one year old. — We collected six specimens in December and January with bursas 300-637 mm2 (x = 444) in size. Three were females in simultaneous molt of the remiges. Three males had plucked ninth juvenal primaries 7-23 mm shorter than plucked ninth basic primaries. Length of plucked juvenal ninth primaries is 209-213 mm (x = 211) and of plucked basic ninth primaries 220-232 mm (x = 225). Testes were 44-75 mm2 (x = 60) in size; ovaries 295-4S0 mm2 (x = 361). There is no doubt that the three females (bursas 300-507 mm2; x = 389) were one year old since they all were in simultaneous prebasic molt of the remiges. We believe the three males (bursas 416-637 mm2; x = 498) were also one year old rather than a few months old because they were collected between 24 December and 6 January, and we think the extensive wear and fading that was evident in their primaries and innermost elongate secondaries would have required as much as a year to attain. 3a. Adults with an estimated minimum age of 22 months. — We collected 20 specimens during October-November that had enlarged gonads (Table 1). We estimate they were in their second or later years of life and were no younger than 22 months. One female lacked the bursa. 3b. Adults with an estimated minimum age of two years. — We collected 14 specimens (nine males, five females) in December and January with bursa small in size (vestigial) and lacking lumen and glandular tissue. Bursas in males were 21-92 mm2 (x = 51) and females 37-72 mm2 (x = 48) in size. In addition, we collected 11 specimens (two males, nine females) in the same period that lacked bursas and one in which it was diseased. Six (five males) of these 26 two-year-old or older specimens were in simultaneous molt of their remiges; the balance had plucked ninth primaries of definitive length. Testes were 30-322 mm2 (x = 134) and ovaries 200-570 mm2 STEAMER-DUCK MOLTS AND PLUMAGES 5 (x = 376) in size. The testes of birds in wing molt (five) were 30-90 mm2 (x = 63) in size, suggesting that wing molt and regres- sion of the testes are correlated. Weller (1965) found that re- gression of testes was correlated with size of bursa in Great Horned Owls (Bubo virginianus) . Lacking specimens of known age, we do not know how long the bursa may be retained in its vestigial state, but wc speculate that female Flying Steamer-Ducks may lose it by the end of the second year and that males may retain it longer. Of 14 females with bursa vestigial or absent, five had vestigial bursas; this was the case for 9 of 11 males. We collected a pair of adults with a brood of /3-grown juvenal birds; the adult male had a vestigial bursa and the female lacked this structure. Weller (1965:105) suggested that atrophy of the bursa of Fa- bricius is associated with sexual maturity. Our data indicate that in Flying Steamer-Ducks, the bursa does not disappear during the first year of life and becomes vestigial or atrophied by the end of the second year and hence that birds of this species may reach sexual maturity toward the end of their second year of life. There are no data on age of sexual maturity in Flying Steamer-Ducks. Weller ( 1972:39-40) speculated that for "Falkland Flightless Steam- er Ducks . . . two years is minimal, and three or more is likely in such territory limited species." In what follows we use the term "adult" to characterize all speci- mens with estimated minimum ages of 22 months and two years. RESULTS Sequence of Molts and Plumages All ten adult male Flying Steamer-Ducks collected at Puerto Deseado and Ushuaia during 11-16 October and 5-17 November had dark caps, grayish-brown cheeks, and white postocular streaks. Three of the Puerto Deseado birds collected during 11-12 October had one or more new white feathers growing in the crown (Fig. 2E). Adult males collected in Ushuaia and Puerto Deseado during 4-26 January were all in heavy molt; seven had old, worn wings and five were in the early stages of growing new remiges. All the birds with old wings had predominantly white head and neck with varying amounts of a new, dark, growing plumage (Figs. 2A, B). Four of the birds with molting wings had entirely dark heads with varying amounts of old white feathers on the neck ( Figs. 2C, D ) ; one had a dark cap, brown cheeks, and white postocular streak. The aforementioned 22 adult male specimens collected in the spring and summer provide conclusive evidence that male Flying Steamer-Ducks have 3 molts and plumages per annual cycle. Flying 6 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY Steamer-Ducks are among the few species of birds known to have three or more molts and plumages per cycle, the others being the Oldsquaw (Clanguh hyemalis), the Ruff (Philomachus pugnax), and ptarmigan (Lagopus spp.) (Palmer 1976, Kozlova 1957, Salo- monsen 1939). Recent unpublished studies (Palmer, in litt.) indi- cate that a number of species of several genera of northern-hemi- sphere waterfowl including Anas and Aythya also have three molts and plumages per definitive cycle. According to Palmer (1972:72-73), the supplemental plumage "may be acquired during a period of molting into either Basic or Alternate, or possibly be offset from Prebasic or Prealternate molt. Not much is known about it." There is considerable overlap in the molts and plumages of those species known to have three or more plumages per cycle. In contrast, the pattern of plumage succession in Flying Steamer-Ducks is relatively simple. For most of the year, male and female adult Flying Steamer-Ducks wear unmixed, readily identifiable plumages on the head and neck. We interpret the sequence of molts and plumages of the head and neck of adult male Flying Steamer-Ducks as comprising: (1) a prebasic molt which at about the time the remiges are dropped, produces a briefly-worn, juvenal-like basic plumage with dark head and neck (Figs. 2C, D); (2) a prealternate molt while the new remiges are developing which results in a head with dark cap, brown cheeks, and white postocular streak, worn about nine months until mid or late spring (Fig. 2E); and (3) a presupplemental molt which results in a predominantly white head and neck worn for one to two months ( Figs. 2A, B ) . Specimens of adult male Flying Steamer-Ducks in supplemental plumages are practically non-existent in museum collections, which accounts for Murphy's (1936:968) statement that "The oldest males . . . have clear gray heads, except for the white postocular stripe and the reddish throat patch." Weller (1976:47) correctly stated that "mature males are white-headed" but believed (1976:46) that "younger males . . . [have] grayish or brownish face . . . [and] white eyestripe." The same sequence of molts and plumages is true for adult females, but the plumages are characterized as follows: ( 1) basic — the head and neck is dark and almost unicolor (Figs. 3B, C); (2) alternate — dark gray cap, white postocular streak, and dark brown cheeks (Figs. 3D, E); and (3) supplemental — dark brown cap, dark reddish-brown cheeks and slight or no postocular streak (Fig. 3A). Adult females appear to undergo the presupplemental molt somewhat earlier than males. In addition, the presupplemental molt in adult males near Ushuaia occurs more than one month later than in Puerto Deseado. At Ushuaia we found no males in presupple- STEAMER-DUCK MOLTS AND PLUMAGES 7 mental molt as late as 17 November and collected white-headed adults just starting prebasic molt as early as 4-6 January. We assigned names to the molts and plumages of steamer-ducks according to the following assumptions: (1) Plumages that more closely resemble the juvenal plumage are evolutionarily more ancient or "primitive" than those which are less similar to the juvenal plumage. (2) Plumages that show less sexual dichromatism are evo- lutionarily more ancient or "primitive" than those which are more sexually dichromatic. (3) The basic plumage is attained by a complete molt of all feathering. In adult Flying Steamer-Ducks of both sexes the plumage of the head and neck acquired immediately prior to and during the onset of the prebasic molt of the wing closely resembles the juvenal plum- age and is most appropriately designated the basic plumage. This is replaced on the head and neck during prebasic molt of the wings by a plumage that exhibits moderate sexual dichromatism, differs in aspect from the juvenal plumage, and is worn for approximately nine months until mid or late spring. Because this plumage is suc- ceeded by one which is strongly sexually dichromatic (see assump- tion 2, just above), we term it the alternate plumage and its successor the supplemental ( Fig. 1 ) . Using the above criteria for determining the names and homolo- gies of plumages, the timing of the simultaneous prebasic molt of the remiges in Flying Steamer-Ducks is "normal" rather than "off- set" (Palmer 1972:74) in that it occurs concurrent with the prebasic molt of the head and body and "soon after nesting." Descriptions of Plumages As far as we can determine, Flying Steamer-Ducks start attain- ing definitive plumages with the second prebasic molt when they are about one year old. The second basic plumage of five one-year- old birds (three males, two females) is indistinguishable from that of older birds. We believe that the second supplemental plumage of the head and neck of males is predominantly white. There may be more white in older birds ( some birds have a pale gray cap and cheeks and some do not) but we have no specimens of known age and the variation may be in part geographic rather than age- related. The following descriptions are presented in ontogenetic order starting with the juvenal plumage and ending with the definitive plumages of the head and neck. Juvenal male. — Forehead and crown dark brownish-black; lores dark brownish-black becoming slightly lighter and somewhat reddish on the face and side of neck; long, narrow, rather faint 8 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY Figure 1. — Idealized diagram of the sequence and approximate timing of molts and plumages in adult Flying Steamer-Ducks of both sexes. The outer ring represents the plumages of the head and neck; the inner solid lines represent periods of molt. PA, prealternate molt; PB, prebasic molt; PS, pre- supplemental molt. whitish postocular streak on one specimen, only suggested on the other; eyelids white; throat and ventral neck dark cinnamon bor- dered by dark gray ( Fig. 4A ) . Two young males in full juvenal plumage on head and neck were collected on 20 and 22 January in Puerto Deseado from a group of five accompanied by a pair of adults. The specimens weighed 2150 and 2200 g, % the weight of the accompanying adult male. Their primaries, including sheaths, were approximately 7 and 10 cm in length. There was no molt on the head and very slight or no molt on the neck. Except for the back, on which there was heavy feather growth in one specimen and none on the other, the other feather tracts of the trunk showed heavy feather growth in both specimens. STEAMER-DUCK MOLTS AND PLUMAGES 9 Juvenal female. — Unknown but probably identical to male. First basic, male and female. — Unknown. First alternate, male and female. — Unknown. First supplemental male. — Forehead and crown dark brownish- gray; lores and cheeks dark grayish-brown with a slightly reddish cast; eyelids white; postocular streak broad and white anteriorly, becoming grayish and then grayish brown and diffuse posteriorly; throat dark cinnamon; neck medium gray, becoming paler ventrally and with medium cinnamon in the ventral neck (Fig. 4B). We collected two first-year males on 29 September (Puerto Melo, Chubut) and 10 October (Puerto Deseado). Both had juvenal wings, were molting, and were in what we judge to be first supplemental plumage with a few worn alternate feathers in the crown. First supplemental female. — Indistinguishable from male. We collected one first-year female with juvenal wings on 10 October at Puerto Deseado. Definitive basic plumages. — The basic plumages of the head and neck of Flying Steamer-Ducks are extremely variable and appear to have three color phases in males and two in females. Both sexes have brown and chocolate-colored phases; males also have a pur- plish-gray phase apparently lacking in females. We do not think these color phases are related to age because we collected two first-year females in full second basic plumage, chocolate phase, that were very similar to four adults in color of head and neck. In addition, the chocolate and brown phases occurred both at Ushuaia and Puerto Deseado. Based on these specimens, we believe the color phases of the basic plumage of the head and neck represent polychromatism. On the head and neck, the basic plumage, chocolate phase, and the juvenal plumage are very similar in appearance. In addition, except for the throat, the basic plumage of the head and neck is unicolor in both sexes and exhibits the least sexual dichromatism of the three definitive plumages. We collected 14 males and 14 females in various stages of the prebasic molt. Three of the males (late December to early Janu- ary) were one year old and in second prebasic molt as were two one-year-old females ( January ) . An additional one-year-old female (January) was in second prealternate molt and retained part of the second basic plumage on the head and neck. All three of the first-year females were in prebasic molt of the wings; the three males in second prebasic molt had juvenal remiges. Definitive basic male: brown phase. — Head and neck dark brown, crown slightly darker; posterior cheeks and side of neck slightly lighter; throat dark cinnamon bordered by medium to dark gray (Fig. 2D). 10 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY Two adult males in prcbasic molt were collected on 26 January at Puerto Deseado; both were growing new remiges. The molt on the head and neck was quite advanced, but both birds retained white supplemental feathers on the neck intermixed with new brown basic feathers. Both birds had a short whitish postocular streak not present in a third adult collected on the same date. This bird had molting wings and heavy body molt in all tracts, and complete basic plumage of the head and neck. Two first-year males from Ushuaia collected on 4 and 6 January, had worn juvenal primaries, heavy body molt in all tracts, and new brown second basic feathers on the anterior part of the head. Definitive basic male: chocolate phase. — Head and neck dark chocolate brown; throat dark cinnamon, bordered laterally by me- dium gray. We obtained no specimens of this phase in full basic plumage of the head and neck but we hypothesize the above description on the basis of one adult specimen collected on 6 January in Ushuaia. This bird had old worn wings, and head and neck mostly in white supplemental plumage. Its forehead, anterior crown, lores, and anterior cheeks had new dark chocolate-brown basic feathers. Since the definitive basic plumage of the head and neck in all other phases is unicolor except for the throat, we suspect this is also true for the chocolate phase. Three additional January specimens, all adults, one from Ushu- aia and two from Puerto Deseado, had old wings and most of the head and neck in white or white and light gray supplemental plum- age. Each of these birds had small patches of new, dark chocolate brown feathers in the anterior forehead and anterior lores. Definitive basic male: purplish- gray phase. — Head and neck dark purplish-gray, throat dark cinnamon bordered by medium gray; very short trace of a whitish postocular streak (Fig. 2C). On 23 January we collected three adult males in prebasic molt at Puerto Deseado. Two of them had old, worn remiges and con- siderable amounts of retained white supplemental plumage on the head and neck; the new incoming basic feathers on both were dark purplish-gray. One bird had wings in molt and the growing pri- maries were approximately 4 cm long. This specimen was in full basic plumage of the head and neck except for a few lighter feathers on the sides and ventral parts of the neck. Figure 2. — Plumages of head of male Tachijcrcs patachonicus. A and B, adults in supplemental plumage with incoming basic feathers (A, KUMNH 79216, 23 January, Puerto Deseado; B, KUMNH 79205, 6 January, Ushuaia); C, adult in basic plumage, purplish-gray phase (KUMNH 79220, 23 January, Puerto Deseado); D, adult in basic plumage, brown phase (KUMNH 79230, 26 January, Puerto Deseado); E, adult in alternate plumage with incoming supplemental feathers (KUMNH 77954, 15 October, Puerto Deseado). STEAMER-DUCK MOLTS AND PLUMAGES 11 B /»*" '-1^- E 12 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY Definitive basic female: brown phase. — Head dark brown, cap darker; neck medium brown; throat dark cinnamon; very short, whitish postocular streak ( Fig. 3C ) . An adult specimen collected on 25 January in Puerto Deseado had old, worn remiges that were easily pulled and apparently about to be shed, and head and neck in what we think was full basic plumage. Another adult collected on 27 December in Ushuaia had old, worn remiges, and apparently retained a few supplemental feathers on the lower neck; otherwise it was like the Puerto Deseado specimen except that the throat was darker cinnamon. Definitive basic female: chocolate phase. — Head and neck dark chocolate brown; throat dark cinnamon, eyelids white; short, faint, whitish postocular streak ( Fig. 3B ) . Two first-year females in second basic plumage were collected on 6 January near Ushuaia and 26 January at Puerto Deseado; they were in heavy body molt in all tracts, and had new growing pri- maries 1 and 2 cm long. We collected four adult females in third or subsequent prebasic molt and chocolate-phase basic plumage on the head and neck. Two of these were collected on 4 and 5 January near Ushuaia and two on 22 and 24 January at Puerto Deseado. One bird was in wing molt, and its head and neck were in full basic plumage indistin- guishable from the second basic plumage of first-year birds. The other three birds had old worn remiges, and retained varying amounts of the supplemental plumage, mostly on the lower neck. The basic feathering of the head and neck on two of these birds was somewhat lighter and more brown than that of "typical" choco- late-phase birds. Definitive alternate male. — Crown medium to dark gray; lores and cheeks medium dull grayish-brown; prominent white postocular streak; throat medium cinnamon ( Fig. 2E ) . We collected 10 adult males between 11 October and 17 No- vember near Puerto Deseado and Ushuaia. All were in full alternate plumage of the head and neck; some specimens showed consider- able wear, especially on the anterior crown and forehead. Three of the birds from Puerto Deseado were just initiating the presup- plemental molt on the head, each of them having one or several new white feathers in the anterior crown. Definitive alternate female. — Forehead and crown dark gray; Figure 3. — Plumages of head of female Tachyeres patachonicus. A, adult in supplemental plumage ( KUMNH 77949, 11 October, Puerto Deseado); B, adult in basic plumage, chocolate phase (KUMNH 79204, 5 January, Ushuaia); C, adult in basic plumage, brown phase ( KUMNH 79222, 25 January, Puerto Deseado); D, adult in fresh alternate plumage (KUMNH 79191, 27 December, Ushuaia); E, adult in worn alternate plumage with incoming supplemental feathers (KUMNH 77950, 11 October, Puerto Deseado). STEAMER-DUCK MOLTS AND PLUMAGES 13 ^ •^ D i p - - ._..*,..: ~^ i %nn fe? 14 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY ^ s> B L *t r^ D / ^n*?. '8f G STEAMER-DUCK MOLTS AND PLUMAGES 15 lores and cheeks dark brown becoming medium brown on sides of neck; white postocular streak occluded posteriorly by medium brown becoming a whitish patch on sides of neck; whitish collar; throat dark cinnamon (Figs. 3D, E). A first-year female collected on 20 January near Puerto Deseado had heavy body molt in all tracts and new primaries 4.5 cm long. This bird was in almost full second-alternate plumage of the head and neck. Two adult females collected on 27 and 29 December near Ushuaia had fully grown new wings. One of the birds was in heavy body molt and the other was molting slightly on the head, belly, and lower back. Both birds were in full alternate plumage of the head and neck. Definitive supplemental male. — Head and neck white with pale gray wash on cheeks, darker on lores; throat medium cinnamon bordered with pale gray ( Figs. 2A, B ) . There is considerable variation in the amount and distribution of gray on the head and neck of birds in supplemental plumage. We suspect that some individuals have completely white head and neck except for a cinnamon patch on the throat. Most individuals we collected had considerable gray on the head and neck varying from having the cap, cheeks, and lores light brownish-gray to the head and upper neck being light or medium gray with a short, narrow white postocular streak. Three males collected at Ushuaia and six at Puerto Deseado during 4-26 January were in various stages of prebasic molt of the head and neck, on which dark basic feathers were replacing white or gray supplemental feathers. Two birds were molting their wings and retained supplemental feathers only on the neck. The other seven birds had old, worn wings and on the head and neck showed the anterior-to-posterior replacement of white or gray supplemental feathers with dark basic feathers. Three specimens with old wings had just started the prebasic molt of the head and neck and had small patches of dark basic feathers restricted to the anterior fore- head and lores. The supplemental plumages of these birds varied from almost completely white to having the cap and cheeks light brownish-gray or with the head and neck light medium-gray with faint white or whitish postocular streak. Figure 4. — Plumages of head of juvenile and 10-month-old Tachyeres patachonicus and colors of feet. A, ;a-grown male in juvenal plumage (KUMNH 79214, 22 January, Puerto Deseado); B, male approximately 10 months old in first supplemental plumage (KUMNH 77944, 10 October, Puerto Deseado); C, foot of juvenal male (KUMNH 79214); D, foot of adult male not in wing molt (KUMNH 79203, 5 January, Ushuaia); E, foot of adult male not in wing molt (KUMNH 79215, 23 January, Puerto Deseado); F, foot of adult female not in wing molt (KUMNH 79229, 26 January, Puerto Deseado); G, foot of adult female in wing molt (KUMNH 79204, 5 January, Ushuaia). 16 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY Four adult specimens with old wings had extensive patches of new basic feathers on the head. The retained supplemental plumage of the head and neck of one of these birds appears to have been completely white except for the throat. Three adult specimens were collected during 11-12 October near Puerto Deseado. All had definitive wings, and were just beginning the presupplemental molt of the head on which one to several new white supplemental feathers were among the worn dark alternate feathers of the crown. Three additional adult birds collected near Puerto Deseado during 5-16 October and four from Ushuaia during 5-17 November had definitive wings and showed no signs of pre- supplemental molt on the head and neck. Definitive supplemental female. — Crown dark grayish-brown; lores and cheeks dark reddish-brown, grading to dark grayish-brown and then darkish medium gray on the neck. There is no pale or white collar at the base of the neck. The postocular streak is short, the white feathers in its posterior part having been replaced by medium-brown feathers (Fig. 3A). We collected 10 adult females between 11 October and 17 November near Puerto Deseado and Ushuaia. Two were in pre- supplemental molt of the head and neck, three were not molting and were in full supplemental plumage of the head and neck, and five were not molting and were in full alternate plumage of the head and neck. The definitive supplemental plumage is quite similar to the alter- nate but differs in lacking the white collar, having a very short postocular streak, and in having a pronounced reddish cast in the lores. Colors of Soft Parts Photographs of specimens collected during 1980-81 enabled us to compare colors of soft parts of Flying Steamer-Ducks by sex, locality, and estimated age. The following descriptions of colors of soft parts are from birds collected during 34 days in December and January representing three age classes: juvenal birds (approxi- mately two months old), one-year-olds, and adult birds two years of age or older ( Table 2 ) . Juvenal male. — Bills of two juvenal males from Puerto Deseado were bluish-black with a trace of dull orange at the base and a bluish-white crescent around the black nail. The feet were dull medium tan and "knuckles" prominently marked with blackish- brown (Fig. 4C). Juvenal female. — Unknown but probably identical to male. First-year male. — Three males from Ushuaia of approximately one year of age, in prebasic molt, and with juvenal wings, had bills medium to dark slaty blue with orange more limited in extent STEAMER-DUCK MOLTS AND PLUMAGES 17 1-1 CU 3 r— cfl •— 05 CU c 05 c G CU G bt G o 5 38 § i— ( >- 3 w CO cu ~< -2 Cv G i- CU CU bt CO 1* G 3 , rt E 4-» M-i 5 c c/3 wa t! 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In addition, the feet were dull tan (orange-tan in one bird) with dark patches on the "knuckles." We lack specimens of one-year-old males from Puerto Deseado. Soft part colors of one-year-old males from Ushuaia are very similar to those of adult males from Puerto Deseado in wing molt except for the feet which are tannish (instead of yellowish) and have more prominent markings on the "knuckles." One-year-old males from Ushuaia also have the nail surrounded by crescent of bluish-white as do definitive males from Puerto Deseado. First-year female. — One first-year female from Ushuaia in wing molt had bill light to medium blue with dull orange at the base and the culmen becoming pale around the black nail. The feet were tannish-orange with dark patches of intermediate prominence on the "knuckles." Two first-year females from Puerto Deseado in wing molt dif- fered from the Ushuaia specimen in having more yellow or greenish- yellow in the dull orange of the bill, a white or whitish-blue crescent around the black nail, and feet light yellow or yellowish-tan with "knuckle" markings faint or intermediate in prominence. An adult female from Ushuaia in wing molt was identical in colors of soft parts to the comparable first-year bird except for slightly less extensive orange on the bill and richer orange feet with more prominent markings on the "knuckles." An adult female from Puerto Deseado in wing molt was very similar to one of the comparable first-year birds except the feet were light orange-yellow. We collected no first-year females that were not in wing molt. Adult male. — Bills of adult males from Puerto Deseado are mostly orange or yellowish-orange with a large area of medium blue below nostril at the onset of the prebasic molt of the head; the feet are rich orange-yellow (Fig. 4E). Birds in wing molt have bills medium to dark slaty-blue with orange much reduced in extent and duller; the feet are paler and yellowish. Three adult males from Ushuaia, all beginning prebasic molt of the head but none in wing molt, differed from comparable birds (four not in wing molt) from Puerto Deseado in having: (1) bills almost entirely orange or yellowish-orange with only a faint wash of bluish below the nostril; (2) orange on upper mandible extending to and surrounding black nail (in Puerto Deseado birds the black nail is surrounded by a crescent of pale bluish-white which is duller, bluer, and less extensive in birds molting their wings); (3) patches on "knuckles" of toes darker and more prominent (Fig. 4D) (most but not all adult males from Puerto Deseado have faint markings on the "knuckles"). We lack adult males in wing molt from Ushuaia. STEAMER-DUCK MOLTS AND PLUMAGES 19 Adult female. — Bills of seven adult females not in wing molt from Puerto Deseado were slate blue; two of them had only a faint trace of dull orange on the culmen; two had dull orange on the culmen extending to the nail; and in three the dull orange occupied approximately the basal half of the culmen and a patch of varying size on the dorsal part of the lateral base of the bill. These varia- tions are not correlated with the extent of the prebasic molt of the head. Five of the seven females had the black nail surrounded by a crescent of pale bluish-white; two had dull orange extending to the nail and in this respect were similar to adult males from Ushuaia. The colors of the feet of these seven specimens were orange- yellow, yellow, or tannish with "knuckle" markings varying from faint or very faint in three birds with yellow feet to more or less prominent in the rest ( Fig. 4G ) . An adult female in wing molt from Puerto Deseado had more extensive dull orange on the culmen and sides of bill at the base than any of the comparable birds not in wing molt. In addition, the rest of the bill was light-medium blue in contrast to the much darker and more extensive slate blue of the birds not in wing molt. The nail was surrounded by a crescent of pale tannish-white and the feet were yellow with faint markings on the "knuckles" (Fig. 4F). Bills of five females not in wing molt from Ushuaia were medium slate blue with limited dull (three birds) or brighter (two birds) orange extending the length of the culmen and becoming paler around the black nail. An adult female in wing molt had a bill identical with those of females not in wing molt but with brighter orange on the culmen. The colors of the feet of the five adults not in wing molt were yellow to orange yellow with "knuckle" markings absent to faint. The adult in wing molt had slightly darker or richer orange-yellow feet with prominent markings on the "knuckles." In summary, bearing in mind that samples are small and repre- sent three estimated age classes collected during a 34-day period during late December and January (Table 2), wc conclude that: (1) There is an ontogenetic change in foot color from dull medium tan in juvenal birds to tannish, yellowish-tan, or yellow in one-year-old birds, to orange-yellow or orange in adult birds not in wing molt. (2) Adult males in wing molt have feet that are more yellow (less orange) than those of non-molting birds. (3) "Knuckle" markings on the feet are prominent in one-year- old and adult males from Ushuaia and faint in comparable males from Puerto Deseado. "Knuckle" markings are prominent in juvenal males from Puerto Deseado and variable in females from both localities. 20 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY (4) Adult males from Ushuaia not in wing molt have orange bills faintly bluish below nostril, and nail surrounded by orange. Comparable males from Puerto Deseado have a large blue patch below nostril and a bluish-white crescent surrounding the nail. (5) Adult males from Puerto Deseado in wing molt have more blue and much less orange in the bill than comparable males not in wing molt. This probably also is true of adult males from Ushu- aia but we lack specimens in wing molt. ( 6 ) There appears to be an ontogenetic progression of bill color from: (a) bluish-black with a trace of dull orange in juvenal birds to (b) light, medium, or slate blue with dull orange limited or ab- sent in one-year-old birds of both sexes and adult females, to (c) orange with large blue patch (Puerto Deseado) or almost com- pletely orange (Ushuaia) in adult males not in wing molt. Bills of adult males in wing molt become female-like in color. DISCUSSION Flying Steamer-Ducks arc the only southern-hemisphere water- fowl for which three molts and plumages per cycle have been docu- mented. The patterns of plumage succession in other species of Tachyeres are poorly known. Although very similar in appearance, Flying Steamer-Ducks from Puerto Deseado and Ushuaia may be taxonomically distinct. Data on skeletal measurements and biochemical characters, not presented here, support this view. In addition, the soft part colors of adult males not in wing molt differ between the two localities. Our samples of specimens of comparable age and plumage are too small to test this hypothesis in terms of plumage characters. We speculate that the white-headed plumage of Flying Steamer- Ducks functions principally in relation to establishment and defense of nesting territories. All adult male Flying Steamer-Ducks we collected during October and November at Puerto Deseado and Ushuaia were in alternate (not white-headed) plumage; none of the paired males we saw or collected had white heads. Males already are paired by the time they undergo the spring presupple- mental molt and are in the white-headed plumage at about the time they are establishing and defending nesting territories. There is evidence that steamer-ducks, especially young birds, frequently occur in flocks throughout the year (Vallentin 1904, Crawshay 1907, Percy in Phillips 1925, Murphy 1936, Pettingill 1965, Woods 1975, Weller 1976). It may be advantageous for Flying Steamer-Ducks to wear the white "combat" plumage only during the season when nesting territories are established and defended, and to have a more "sociable" plumage the rest of the year. At times, food resources may be found and utilized more effectively STEAMER-DUCK MOLTS AND PLUMAGES 21 and safely by birds in flocks (Rand 1954, Ward and Zahavi 1973, Caraco 1979). Although we have no data from marked birds, we believe that the prebasic molt in adult steamer-ducks occurs after nesting as in many other species of waterfowl. We collected a pair of adult Flying Steamer-Ducks on 20 January 1981 near Puerto Deseado accompanied by a brood of five %-grown juvenal birds. Both adults were in heavy prebasic molt of the head, neck, back, and upper breast but retained the old primaries. On 17 February at Puerto Melo, we collected a pair of adult T. leucocephalus accompanied by several large juvenal birds. Both adults were in moderate to heavy molt in various regions of the body; the male was in wing molt with new primaries approximately 7 cm in length. The peak nesting season for steamer-ducks appears to be during the austral spring and summer (October-January) but for three of the species there is evidence of nesting all seasons of the year. Murphy (1936:961) reported for T. pteneres that "older young, and fledglings with very short sprouting primaries include odd birds or entire broods taken in Cockburn Channel, March 5; Bertrand Island, April 22; Gable Island, Beagle Channel, May 4; Chiloe, May 19; and Ushuaia, July 19." Cobb (1933:81) stated that for T. brachypterus "nesting proper commences in September, but odd nests have been found all through the months of the year." "Oustalet (1891:229) reports newly hatched young [of T. pa- tachonicus] in Beagle Channel on November 13 and February 1 . . ." (Murphy 1936:972). "Three [fledglings] of the flying species . . . were taken at Ushuaia on April 1. At the same period adults in the vicinity had lost most of their rectrices, while the remiges were in the midst of moult, old worn primaries standing in juxtaposition with fresh ones" (Murphy 1936:971). Weller (1972:44) stated that in the Falkland Islands "Reproduc- tive behaviour patterns are influenced by a climate moderated by the sea and, although seasonal breeding is common in Upland Geese [Chloephaga picta] and Kelp Geese [Chloephaga hybrida], nests of Crested Ducks [LopJwnetta specularioides] and Chilean Teal [Anas] . . . have been recorded in all months of the year." Since a maritime climate prevails as well throughout coastal Pata- gonia, the Fuegian archipelago and along the Pacific coast of south- ern Chile, we suspect that steamer-ducks in those regions may nest throughout the year with the principal reproductive season concen- trated in the austral spring and summer. This would account for cases reported by Murphy ( 1936:961, 971) of steamer-ducks in wing molt during fall (April and May). Another explanation for steamer-ducks molting their wings in the austral fall is that they molt their wings twice annually as do 22 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY stiff-tails (Oxyura spp.) (Frith 1967, Siegfried 1970, Palmer 1976). We feel, however, that late nesting is a more likely explanation for autumnal wing molt in steamer-ducks. D. Bridge and P. Angle collected three specimens of Flying Steamer-Ducks at Isla de los Estados in moderate to heavy body molt on 25 May 1971. The one female preserved as a skin (USNM 536,351) had slightly worn wings, and had supplemental plumage on the head being replaced anteriorly by new, dark basic feathers. The specimen clearly indicates that some individuals of this species undergo the prebasic molt in late fall, presumably having nested somewhat earlier. Bridge and Angle also collected four specimens (two males and two females preserved as anatomical specimens) of T. pteneres during 1-12 May 1971 at Isla de los Estados in heavy molt; three were molting their wings. The most reasonable explanation for the fall wing molt of these birds is that autumnal nesting delayed the prebasic molt. Weller (1976:47) noted that in steamer-ducks "sexual dichroma- tism is reduced in comparison with that of most northern Anatinae." We agree that this is so for T. pteneres. There is, however, marked sexual dichromatism in adult T. patachonicus in supplemental plum- age for approximately two months, adult T. brachijpterus when males have predominantly white heads (possibly supplemental plumage) and adult T. leucocephalus in which the males have white heads 10-11 months of the annual cycle (Humphrey and Thompson 1981). Adult Flying Steamer-Ducks are not sexually dichromatic in basic plumage (of the same phase) worn for about one month, moderately sexually dichromatic in alternate plumage (9-10 months ) , and markedly dichromatic in supplemental plumage ( 1-2 months) during the nesting season. The timing of these plumages appears to be closely linked with the time of reproduction which may occur throughout the year but is most frequent during No- vember-January. SUMMARY Adult Flying Steamer-Ducks 1) have three molts and plumages per cycle, 2) are sexually dichromatic except in basic plumage, 3) are polychromatic (have color phases) in basic plumage of head and neck, and 4) have simultaneous prebasic molt of the remiges. Data from 57 specimens of Flying Steamer-Ducks (T. patachoni- cus) collected during September-November 1979 and December 19S0-January 1981 in Ushuaia (Tierra del Fuego), Puerto Deseado (Santa Cruz) and Puerto Melo (Chubut), Argentina, indicate that this species has three molts and plumages per annual cycle. These are in adults: (1) a prebasic molt into a briefly worn, non-sexually dichromatic, juvenal-like basic plumage; (2) a prealternate molt STEAMER-DUCK MOLTS AND PLUMAGES 23 into a moderately sexually dichromatic alternate plumage worn about nine months; and (3) a presupplemental molt into a strongly sexually dichromatic supplemental plumage when the head of males is mostly white, worn one to two months in the austral spring. The molts and plumages of first-year birds are poorly known. Flying Steamer-Ducks are the only southern-hemisphere water- fowl for which three molts and plumages per cycle are known. In Flying Steamer-Ducks the bursa of Fabricius probably does not disappear during year one and evidently becomes vestigial or atrophied by the end of year two when birds may reach sexual maturity. Plumages of the head and neck and colors of soft parts are described for juvenal, first-year, and adult specimens aged by size of bursa and gonads and juvenal versus adult remiges. RESUMEN Los adultos del Pato Vapor Volador tienen: 1) ties mudas de plumaje en cada ciclo anual, 2) dicromatismo sexual con excepcion del plumaje basico, 3) polycromatismo en el plumaje basico, y 4) muda prebasica simultanea de las alas. Datos de 57 ejemplares de Pato Vapor Volador (Tachyeres patochonicus) coleccionado durante los meses de Septiembre a Noviembre de 1979, Diciembre de 1980 y Enero de 1981 en Ushu- aia (Tierra del Fuego), Puerto Deseado (Provincia de Santa Cruz), y Puerto Melo (Provincia de Chubut), Republica de Argentina, indican que la especie tiene tres mudas de plumaje en cada ciclo anual. Estas son en adultos: 1) una muda prebasica que resulta en un plumaje llevado corto tiempo que parece el plumaje juvenil y falta dicromatismo sexual; 2) una muda prealternada que produce un plumaje llevado aproximadamente 9 meses y que tiene dicroma- tismo sexual moderado; y 3) una muda presuplementaria que resulta en un plumaje llevado 1 a 2 meses en la primavera austral el que tiene dicromatismo sexual bien marcado y en el que la mayor parte de la cabeza del macho es blanca. Las mudas y plumajes de in- dividuos de un afio o menos de edad son poco conocidas. El Pato Vapor Volador es la unica especie de la familia Anatidae en el hemisferio del sur en que se ha descubierto tres mudas y plumajes por ciclo. Los datos sugieren que en el Pato Vapor Volador la bolsa de Fabricius no desaparece durante el primer ano de vida y se reduce a un vestigio al fin del segundo ano cuando posiblemente se llega a la madurez sexual. Los plumajes de la cabeza y del cuello cstan descritos para ejemplares classificados como: 1) juveniles, 2) del primer ano y 3) adultos. 24 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY ACKNOWLEDGEMENTS Our field research in Argentina would not have been possible without the generous assistance of many people and organizations. We are grateful to the following: Bernardo Mayer, Mr. and Mrs. Folmer V. T. J. Faming and their associates at Patagonia Comercial, Chubut, for providing warm hospitality and facilities for field work at Puerto Melo. Dr. Oscar Kuhnemann for arranging for us to work at the Estacion de Biologia Marina, Puerto Deseado, and the Estacion de Biologia Marina Austral, Ushuaia, and Jorge Sesti and Pedro Medina of those two stations. Dr. Jose Maria Gallardo, Director, Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" (M.A.C.N.), Sr. Rogelio A. Bockel, Jefe de Servicios Publicos, and the administrative staff of the Museum. Dr. Jorge Navas for space and facilities in the ornithology section of the M.A.C.N. Dr. Eduardo O. Gonzalez Ruiz and his colleagues, Direccion Nacional de Fauna Sylvestre, for providing permits for field work in Tierra del Fuego and to export specimens. Ing. Qca. Lidia O. Saigg de Chialva, Directora de Protection Ambiental, Provincia de Chubut, and Dr. Daniel Horacio Soria, Director General de Ganaderia, Provincia de Santa Cruz, for issuing permits for scientific collecting in their provinces. Dr. Arturo Tarak, Direccion Nacional de Parques Nacionales, Dr. Guillermo A. Giaroli, Subsecretario de Recursos Naturales Renovables y Ecologia de la Nation, and Seiiores Fernandez Lobbe and Florencio Villar, Ceremonial, Ministerio de Economia, for their assistance in making arrangements essential to the success of our field work. Lie. Gabriela Piacentino, for her concern for the success of our field work in Puerto Deseado, and Yolanda Lucero and Pablo Canevari for obtaining dry ice to save our frozen tissue samples. Dra. Beatriz de Ferradas, Prof. Luis Orquera, and Lie. Ernesto Piana for their hospitality and for helping us obtain supplies and equipment. Mr. and Mrs. Ralph Gibson for being home and family in La Lucila. William Conway, Roberto Straneck, Francisco Erize, Pablo Canevari, David Bridge, Philip Angle, and Oscar Salzgeber for lending slides of steamer-ducks. Mauricio A. E. Rumboll, Pablo Canevari, Francisco Erize, Ro- berto Straneck, and William Conway for their interest in our re- search and for sharing their knowledge and impressions about steamer-ducks. STEAMER-DUCK MOLTS AND PLUMAGES 25 Sr. Ignacio Torres, Supervisor de Cuentas Comerciales, Braniff International, and Abel Arnoldo Gonzalez, Aerolineas Argcntinas, for arranging for thermoses of liquid nitrogen to be flown with us as accompanied luggage. Professor Frank B. Cross for serving as Acting Director, Museum of Natural History, during Humphrey's research leave, and the Museum staff, and Jane Rawlings for holding the fort so well for so long. Robert M. and Marion Mengel and their colleagues in the Divi- sion of Birds and Robert Patterson for cataloging, cleaning, num- bering and labelling skeletal specimens with extraordinary rapidity and good will. The authorities of the University of Kansas for awarding Hum- phrey research leave for three months. Mary Lou Humphrey for her patience and enthusiastic support. D. Bennett for the line drawing. Robert M. Mengel for painting the three color plates and for suggesting improvements in the manuscript. Kenneth C. Parkes and an anonymous reviewer for constructive criticisms of the manuscript. The Kansas University Endowment Association, Southwestern College, Dr. and Mrs. W. Saul, Prof. M. C. Thompson, Mr. and Mrs. L. A. Osborne, Dr. R. T. Peterson, Dr. T. Mastin, Mr. R. Hamilton and the Humphrey family for funds that made possible the field research during 1979. This study was partially supported by National Science Founda- tion grant no. DEB-8012403. LITERATURE CITED Caraco, T. 1979. Time budgeting and group size: a theory. Ecology 60: 611-617. Cobb, A. F. 1933. Birds of the Falkland Islands. H. F. & G. Witherby, Lon- don. 88 pp. Crawshay, R. 1907. The birds of Tierra del Fuego. Bernard Quaritch, Lon- don. 158 pp. Frith, H. J. 1967. Waterfowl in Australia. East-West Center Press, Hono- lulu. 328 pp. Humphrey, P. S. and M. C. Thompson. 1981. A new species of steamer-duck (Tachycres) from Argentina. Univ. Kansas Mus. Nat. Hist. Occas. Pap. No. 95. 12 pp. Kozlova, E. V. 1957. [Evolution of seasonal plumages in Ruff.]. Zool. Zh. 35:1908-1910. (Russian with English summary.) Murphy, R. C. 1936. Oceanic birds of South America. Vol. 2. Am. Mus. Nat. Hist., New York. Pp. 641-1245. Palmer, R. S. 1972. Patterns of molting. Pp. 65-102 in D. S. Famer and J. R. King, eds. Avian biology, Vol. 2. Academic Press, New York. 612 pp. Palmer, R. S. 1976. Handbook of North American birds. Vol. 3. Yale Univ. Press, New Haven and London. 560 pp. 26 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY PETTiNGrLL, O. S., Jr. 1965. Kelp Geese and Flightless Steamer Ducks in the Falkland Islands. Living Bird 4:65-78. Phillips, J. C. 1925. A natural history of the ducks. Vol. 3. Houghton Mifflin Co., Boston and New York. 383 pp. Rand, A. L. 1954. Social feeding behavior of birds. Fieldiana, Zool. 36:1-71. Salomonsen, F. 1939. Moults and sequence of plumages in the Rock Ptar- migan (Lagopus mutus [Montin]). Dansk. Naturh. Foren. 103:1-491. Siegfried, W. R. 1970. Double wing-moult in the Maccoa Duck. Wildfowl 21:122. Vallentin, R. 1904. Notes on the Falkland Islands. Mem. & Proc. Man- chester Lit. Philos. Soc. 48:23-45. Ward, P. and A. Zahavi. 1973. The importance of certain assemblages of birds as "information-centres" for food-finding. Ibis 115:517-534. Weller, M. W. 1965. Bursa regression, gonad cycle and molt of die Great- horned Owl. Bird-Banding 36:102-112. Weller, M. W. 1968. Notes on some Argentine anatids. Wilson Bull. 80: 189-212. Weller, M. W. 1972. Ecological studies of Falkland Islands waterfowl. Wild- fowl 23:25-44. Weller, M. W. 1976. Ecology and behaviour of steamer ducks. Wildfowl 27:45-53. Woods, R. W. 1975. The birds of the Falkland Islands. Compton Press, Ltd., Wiltshire. 240 pp. STEAMER-DUCK MOLTS AND PLUMAGES 27 3 -a > C 3 a o ca cl. Oi „ >— > 03 PL, u ... c « O c t5 £ 3 c a-i o. a a g Cu _ ?«" CJ .„ — 3 O ^ ■s — < — 03 C > 3 i; = < X u < — en c Ol .s * a o pa 01 T3 a - Oi no pa " rt o X o> £ > £ -00 Id , £ o> en z a; sr « 3 Ph T3 0 C ^ T3 - ca "V- CD CI CD C p. 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