n A eee RNS nea co Nhl nak ate Steet: Se asmi vane 25 ei eel ad ad pate vit aie - ai ee Sue < mt Ase Sap a nk a: =e 20 Se ‘ Oot OS 2-55 . _ ~ e © ‘ ay “ \ » ~ - : : oe 5 a i. - _ J any . q — ij : - _ _ : 7 — 7 - rom Dg MNase om ae rn a a ster a iOS in aatitliniecey. Ce _— ee ‘epeury ‘OleyuG Woyyou Jo uoIe1 Avg UOospnyy ayy Ul spunols Hurpoorq oy UO UOLUUTOD OL OLOYY UMOYS OdA] OY JO SJSOU OSOOF) *SHOUTT[T UL AOVUTAL FEIT aso08 Bpvury oy) JO Spunoss Durpseiq oyy uo opis uvipuy vey —"[ “By Ne ee er ee er rece ee eee A _— ; . AS, - > Aad lar Gag pee 2 y : ats. , a pei Fh. : = y is, tid eh : . : fad iat natal . ; A 4 2 Aw 4 was ~ ~—— -« ‘ . J a - iF ae 9 Ped 5 f: ad - ~- ° > ¢ - ka. ~ - . * Z - Aad 2 Td hve ° f, +o Ist. : ; 1 . (CHARACTERS OF AGE, SEX, AND SEXUAL MATURITY IN CANADA GEESE The base upon which the year-to-year manage- ‘ment of a wild goose population must rest is a collec- tion of accurate data on the age and sex of individuals ‘in the population. Age and sex data collected during the fall and winter period can be used to make fairly accurate estimates of the productivity of a population in the previous nesting season and the probable num- ber of geese that will be returning to the wintering grounds in the following autumn (Hanson & Smith 1950:170-171, 192). The validity of these estimates is ‘in large measure dependent on the ability to distin- guish yearling adults from older adults as well as from immatures. External morphological criteria use- ful in aging and sexing Canada geese, Branta cana- _densis, in autumn and winter were summarized earlier (Hanson 1949). Subsequent studies on both the win- tering and breeding grounds have provided additional criteria and established their relative values at various seasons of the year. ACKNOWLEDGMENTS In making the studies reported here, the writer received the support of many organizations and indi- viduals. Studies at the Horseshoe Lake State Wildlife Refuge, Alexander County, Illinois, benefited greatly from the outstanding facilities and co-operation pro- vided by the Illinois Department of Conservation. Field studies conducted in the Hudson-James Bay region of northern Ontario, on the breeding grounds _of the Mississippi Flyway population of Canada geese, Branta canadensis interior, were made possible by a series of grants from the Arctic Institute of North America. Logistic support was provided by the On- tario Department of Lands and Forests. An oppor- tunity to study the population of Branta canadensis maxima wintering at Rochester, Minnesota, was of- fered by the Minnesota Department of Conservation and the U.S. Bureau of Sport Fisheries and Wildlife. (Prior to the writer's rediscovery of this race in Janu- ary, 1962, B. c. maxima had been thought to be extinct since about the turn of the century.) Studies of skin collections were made at the American Museum of Natural History, the National Museum of Natural History, and the Chicago Museum of Natural His- tory. The interest and encouragement of Dr. Thomas G. Scott, Head of the Section of Wildlife Research, Illinois Natural History Survey, has been important to the success of the author's long-term study of the HAROLD G. HANSON Canada goose. The presentation of the findings has benefited from the reviews of the editorial board of the Section of Wildlife Research and the editing of James S. Ayars, Technical Editor of the Survey. Dr. A. V. Nalbandoy of the College of Agriculture, University of Illinois, kindly provided the gonado- tropic hormone used in an experiment mentioned later in this paper. The photograph used for the cover of this publica- tion shows Canada geese on Horseshoe Lake, Alexan- der County. This and most other photographs repro- duced here were taken by the author; photographs for Figs. 9 and 11 were made by Wilmer D. Zehr, Natural History Survey photographer. MATERIALS AND METHODS Present findings are based on trap and/or bag samples of Canada geese at Horseshoe Lake, Alexan- der County, Illinois; at Rochester, Olmsted County, Minnesota; in northern Ontario along the Sutton River, Fig. 1, which drains into Hudson Bay; and on Akimiski Island in James Bay. In the subsequent discussions, the following age classification is used for Canada geese during the fall and winter period: immatures, 5-8 months of age; yearlings, 17-20 months of age; and adults, 29 or more months of age. During the spring and summer, four age classes of Canada geese can be recognized: gos- lings, yearlings, 2-year-old adults, and old adults (not all 2-year-old geese can be separated from older adults ). Except as noted, the discussions below per- tain to sexing and aging geese during the fall and winter period. Immature Canada geese can be separated from older geese on the basis of plumage characters alone, but, for the identification of yearlings and for sex determination, the cloaca must be inspected. Another character useful in age and sex identification is the extensor portion of the carpometacarpus of the wing which, in the male, tends to form a bony spur or knob from repeated injury as the bird ages. Although this paper deals primarily with the char- acteristics of the Hudson Bay Canada goose ( Branta canadensis interior) after attaining flight stage, pho- tographs of growth stages of gosling giant Canada geese (Branta canadensis maxima) are included at the end of this second printing, Fig. 13. PLUMAGE CHARACTERS The tail feathers, the primary feathers of the wing, and the feathers of the breast and belly are all use- ful in determining age in Canada geese. Tail Feathers—The frayed or notched tip in the tail feathers of immature waterfowl, first shown to be a character of age by Beebe & Crandall (1914) and later described by Schigler (1924) and others, has been widely employed by waterfowl biologists (Elder 1946:98; most instances, the tail as a criterion of age Hanson 1949:179), Fig. 2. In feathers of the first postnatal plumage may be readily differentiated from those of the adult plumage by Fig. 2 Tail feathers of Canada geese: notched tip is evident in most of the feathers of the immatures D { and B, immatures in winter; C their narrower, more tapered outline and their less in- tense pigmentation. During the winter, the tail feath- ers of the immature plumage are gradually replaced by the longer, broader, and more deeply pigmented tail feathers characteristic of adult plumage. The tail feathers are generally replaced two at a time, begin- ning with the central pair. In immature Canada geese in southern Illinois, replacement of tail feathers in winter is largely limited to the central two or three pairs. Observations made in early May, 1959, on the breeding grounds of these geese in northern Ontario, revealed that the tail feather criterion of age could be employed, with nearly comparable accuracy, during adult in winter; D, immature in early May. A B ‘ Fig. 3.— Primary feathers of an adult Canada goose, A, and an immature, B, in winter. Feather tips of the adult are rounded; those of the immature are pointed. the migration period, the last half of April and the first half of May. Most yearlings retained some im- mature type tail feathers until the onset of the molt. The above findings apply particularly to Branta canadensis interior of the Mississippi Flyway. That they do not apply equally well to all races of Canada geese became apparent in late January, 1962, when 100 individuals of the subspecies B. c. maxima, the giant Canada goose, were examined by the writer at their major wintering area, the city park of Rochester, Minnesota, and the nearby surrounding countryside. Plumage characters of the immature B. c. maxima at Rochester revealed these geese to be in a much more advanced stage of development at a comparable date than the immatures of B. c. interior in southern Illi- nois. The tail molt was especially well advanced in the Minnesota birds; at least 5 of the 40 immatures examined had a complete set of adult-type tail feath- Fig. 4.— Dorsal view of lower back and tail of a lesser Canada goose, Branta canadensis parvipes, shot at Perry River, Northwest Territories, on July 3, 1949. The faded, pointed primaries of the immature plumage contrast with the black, adult-type tail feathers. late-hatched Fig. 5.—A still retained, in late February, the breast feathers of the juve- nile plumage. The prominence of the shaft in each feather gives the breast a streaked appearance. immature Canada goose that ers. This difference is not surprising, as B. c. maxima breeding on Dog Lake, Manitoba, build nests (Klop- man 1958:169) at least a month earlier than B. c. in- terior, which nest in the Hudson Bay lowlands of northern Ontario and Manitoba. It is advisable to consider both the nesting phenology and the char- acteristics of the individuals of populations before using collections of tail feathers to obtain age ratios. Primary Feathers. —When some of the immature geese in a population have a complete set of adult- type tail feathers in winter, the outermost primary feathers of the wings fortunately provide the investi- gator with a reliable guide to age determination. The primaries of the immature are pointed; those of the adult are obtuse or rounded, Fig. 3. Cloacal characters in wintering birds provide a nearly infallible guide for distinguishing immature males from adult males; however, the cloacal difference between immature and yearling females is largely limited to the depth of the bursa, which is variable. The use of the primary feathers of the wing for age determination probably has its greatest potential value in taxonomic studies of museum skins. In mak- ing a recent study, in various museums, of the skins of races of Canada geese, the author noted specimens that were labeled as to sex but not age or that were incorrectly aged. In these instances a preliminary age determination was made by inspection of the tail feathers and, if these were of the adult type, a con- clusive determination was made by inspection of the tips of the primary feathers. Primaries of geese col- lected in late spring or early summer prior to the molt are usually badly faded by the sun, particularly those of immatures. Being pointed and badly faded, the tips of the primary feathers of the immatures stand out in sharp contrast to the fresh, black tail feathers, Fig. 4, which usually are not attained in full complement until at least midwinter, several months after tail feathers of adults have completed growth. Breast and Belly Feathers—Taverner (1931:31) and Elder (1946:101) have pointed out that breast and belly, or contour, feathers can serve to differenti- ate immatures from older geese. Breast feathers in the juvenile and postjuvenile plumages of immatures are narrower than in subsequent plumages. They are readily recognized by the prominence of the shaft in each feather, which gives the breast a streaked ap- pearance, Fig. 5. Usually these feathers are replaced during the first winter of life by broader contour feath- ers, which give the underparts a smoother appear- Fig. 6.— Incubation patches of adult female Canada geese during early stages of incubation: A, a 2-year-old with a clutch of three eggs, June 3; B, an old adult with a clutch of seven eggs, May 28. 6 Fig. 7. — Adult female Canada geese in winter with, A, partially pigmented and, B, unpigmented contour feathers on s‘tes of former incubation patches. ance and a more even coloration. Geese in their second winter of life, and older geese, have wider— and somewhat stiffer—breast feathers. Although dif- ferences in shape, coloration, and texture of breast feathers might possibly prove useful in aging geese if no other characters were available, the time re- quired for accurate age determination from these feathers does not make their use an efficient technique. In late spring and the early part of summer, a sexually mature female that has produced eggs can be distinguished from a sexually immature yearling and from a nonproductive, older adult female by the presence, on the lower breast and belly, of a bare or partially bare area known as an incubation patch, Fig. 6. This area, from which the female has pulled feath- ers during the incubation period, is subsequently re- feathered. By the onset of the wing molt, or shortly thereafter, when the incubation patch has become refeathered, the fresh, unfaded, and unworn feathers stand out in sharp contrast to the worn and faded feathers of the rest of the breast and belly. The patch feathers, therefore, serve to identify a productive fe- male throughout the flightless period in summer. After this period, the remaining old feathers of the underparts of the body are replaced by new feathers, and the feathers of the patch area may become in- distinguishable from the rest of the underparts. In a small percentage of females, the patch area produces some white or atypically colored feathers, Fig. 7. These feathers are retained until the next spring and hence, during the winter period, indicate the site of the pre- vious incubation patch (Hanson 1959:145). THE WING SPUR The extensor portion of the carpometacarpus bone of the wing can be used in aging geese. In the im- matures and yearlings of both sexes in the wintering populations, the skin at this portion of the wing re- mains feathered, Fig. 8A. In adult females, the tip may be partially bare as a consequence of earlier nesting activities. In sexually mature adult males, the tip of the extensor portion of the carpometacarpus is en- larged and sometimes notably knobby, and the skin over it is usually partially denuded of feathers, Fig. 5B. This condition is a behavioral or anatomical artifact, the result of repeated injury in fights with other adult males. The development of a clublike tip to the ex- tensor serves to increase the effectiveness of the wing as a weapon of defense. Fig. 8.— Wing of yearling male Canada goose, A, and of an adult male, B. The enlarged, knoblike portion of the car- pometacarpus of the adult is conspicuous. THE CLOACA Within the past quarter century, characters of the cloaca have become widely recognized as criteria of sex and age in waterfowl (Gower 1939; Hochbaum 1942; Elder 1946; Hanson 1949). A Canada goose can be most easily subdued for examination of the age and sex characters of the cloaca if the goose is held upside down on the operator’s lap and the breast of the bird is firmly tucked under the operator's chest. The goose can be readily placed in this position if the operator grasps the bird across the humeri with one hand so that the front of the bird is toward the op- erator. The bird is in position to be placed on the operator's lap with a half-turn of his hand. If the bird is first held so that it faces away from the operator, it must be turned end over end to be in position for examination. It is awkward to handle a goose in this manner, and the abrupt change in position causes the bird to increase its struggles. The struggles of a bird being held can be greatly minimized if its head and neck are tucked under one wing. Internal examination of the cloaca with the aid of a nasal speculum, Fig. 9, is relatively simple provided the goose is securely held. A metal rod about 2 mm in diameter and with a smoothly rounded tip should 8 be used as a probe. Extending the cloaca greatly fa- _ cilitates probing for the bursa. The oviduct attaches _ to the left wall of the cloaca about 15 mm below the sphincter muscle. To explore the cloaca for an open- ing to the oviduct, the operator should hold the specu- lum at right angles to the axis of the bird’s body. The site of attachment of the oviduct is most easily in- spected if the probe is held nearly parallel to the left wall of the cloaca and moderate lateral pressure is used to stretch and smooth out the tissue in that area. A speculum can be used with no harm to the bird if the cloaca is spread open rapidly and firmly. Repeated, gingerly made attempts, in addition to causing the bird to struggle, are apt to rupture small blood vessels. The Sphincter Muscle—The size, conformation, and color of the external bare area of the sphincter muscle, Fig. 10, provide some immediate clues to the age and sex of the bird being handled. In immatures of both sexes, the sphincter muscle is flat, small in diameter, and pink-red in color. In yearlings, in winter, the bare area is somewhat larger and may be slightly darker in color. In older, sexually mature geese, the sphincter muscle is usually a darker red or varying hues of purple. Adult males can usually be distin- guished from adult females by the marked convexity of the muscle in the males. In adult females, the bare Fig. 9.— A, method of using speculum and probe to explore the proctodeum of the cloaca of a Reach moo in tape or absence of a bursal opening; B, method of exploring the cloaca to determine whether or not the oviduct is open at its j ture with the cloaca. 9 q meet ; ; i a { j : / : é / | : . i / : | : | Fig. 10.— Anal sphincter muscles of female Canada geese in winter: muscle in repose; C and D, the muscle partially everted. 10 A and C, immature; B and D, adult; A and B, the area of the muscle is particularly large and flat in cross section, Fig. 10B and D, and the extent to which it can be readily everted usually distinguishes females of this age class from yearling females, Fig. LOA and C.. The Bursa of Fabricius.—Use of the bursa of Fabricius to distinguish immature from older water- fowl has been described, with reference to ducks, by Gower (1939:427) and by Hochbaum (1942:304-306 ) and, to Canada geese, by Elder (1946:106-108 ). Be- cause Canada geese require a longer period to become sexually mature than do most common species of ducks, the bursa of Fabricius is a useful age criterion for distinguishing yearling geese, in winter, from sexually mature adults (Hanson 1949:179-180). The depth of the bursa in immatures ranges be- tween 24 and 35 mm. The average is about 27 mm. In yearlings, it varies between 15 and 24 mm and averages about 20 mm. The bursa is either closed or has been resorbed in approximately 58 percent of geese in their third winter of life; the remainder have a bursal depth varying from 17-21 mm and an aver- age depth of 15 mm. Penis characters must be es- pecially carefully evaluated in aging these males. As a criterion of age in Canada geese, the bursa is of value chiefly in separating yearling from older geese, but it must be used in combination with other cloacal char- acters. Absence of the bursa can be considered quite certain evidence that a goose is 24 or more years of age. Closure of the bursal opening into the proctodeum of the cloaca apparently proceeds most rapidly during the second year of life, that is, in the age group achiey- ing sexual maturity in the third spring of life. A fe- male, Fig. 6A, shot along the Sutton River, Ontario, near the coast of Hudson Bay in early June and judged to be nesting for the first time, had a clutch of three eggs, a very restricted incubation patch, and a bursa that had membranous walls that could be probed only with difficulty. She was judged to be nearly 2 years of age. The Oviduct.—In female Canada geese, the mem- brane that occludes the opening of the oviduct into the cloaca is usually not resorbed until after the geese = — i | Hi Hilt i ! tl Fig. 11.— Penis of, A, an immature Canada goose during the first winter of life; B, a yearling during its second winter of life; and, C, an older adult in winter. The stage of development the penis a yearling, D, attains during its second spring of life (an immature the previous winter) is nearly comparable to that attained by an adult, E, in spring. have left their wintering grounds in their third spring of life. Therefore, determining the presence or absence of an occluding membrane at the juncture of the ovi- duct with the cloaca is the best way, in winter, to distinguish females approximately 1'2 years old from older females. Accurate age determination is of singu- lar importance if the success of the past breeding sea- son is to be estimated from age and sex ratios obtained from trapped birds prior to the hunting season. Studies conducted in preparation for an earlier report (Han- son 1949:181-182), based on banded birds of known age, indicated there was a high degree of accuracy in Fig. 12. hormone: 18 days; C, and gonadotropic hormone; E, light and gonadotropic hormone injections daily for 18 days. 12 differentiating females 142 years of age from those older. In approximately 97 percent of the cases, a female goose that, in fall or winter, has adult-type tail feathers, adult-type primary feathers, and a closed oviduct is approximately 1% years old; if she has an open oviduct, she is about 2'2 years of age or older. (In a few individuals, the oviduct may open in the second spring of life. ) and es- The Penis.—For most species of geese pecially for the immatures—determining the presence or absence of a penis is essential to accurate sexing. Eversion of the penis from the cloaca of a male bird Stages of development of the penis of Canada geese as shown by an experiment involving use of light and A, adult male, untreated in early February; B, yearling male, March 2, after receiving 16 hours of light a day for captive yearling male, April 11, caged outdoors; D, yearling male that received daily, for 4 days, 16 hours of light stage intermediate between D and F; F, yearling male, March 2, after being given 16 hours of is a simple matter in ducks; in geese, because of the larger size and greater strength of the sphincter mus- cle, eversion is more difficult. The technique is the same in both cases—application of a firm downward and outward rolling pressure of the thumbs when placed on either side of the sphincter muscle. The forefingers are used to bend the tail back to aid ever- sion of the cloaca. At the same time an upward pres- sue is applied from below the bird by a lateral surface of the middle finger of each hand. Experience in sexing geese and in examining the cloaca with the speculum is probably best gained, at first, by working with dead birds. The presence of an immature penis in a wild goose being examined immediately identifies the bird as an immature male. (Captive geese sometimes de- velop more slowly than wild geese, and some cap- tive yearling males may have immature penes.) The everted penis of an immature will be seen as a small, corkscrew-shaped organ (about the size of the ex- posed lead tip of a sharpened pencil) situated in the 8 o'clock position, Fig. 11A. Present in female geese is a small papilla on the internal edge of the sphincter muscle. This papilla, situated in the 6 o'clock position, is minute in im- matures but somewhat larger in older females. It is believed to be homologous to the clitoris in mammals. The penis of the yearling male goose in winter, Fig. 11B, can be described as intermediate in size be- tween that of an immature and an adult, Fig. 11A and C. In the great majority of instances, penis characters, when considered together with the bursa, are useful in distinguishing yearling adults from older adults. The penis in yearlings is about 4 mm in diameter and 10 mm long. Its most salient features, a pale, translucent color and a smooth surface appearance, Fig. 11B, tend to give it a rather turgid aspect. The sheathed and unextended penis in older geese, in winter, is generally one and one-half to two times as large as this organ in typical yearlings. It is usually a darker red than the penis in yearlings and is some- times tinged with purple, particularly toward the distal end. The surface of the sheath is wrinkled in appearance, and the visible venation is more prom- inent than that of yearlings. No discernible change in the development of the penis is seen in wintering immatures prior to north- ward migration in late February and early March, but in yearlings and adults some enlargement and a tendency to become unsheathed may be noted. By the time Canada geese arrive on the breeding grounds in late April and early May, the penes in all age classes have undergone notable development, Fig. 11D and E, particularly the penis of the immature. In the 2- month interval between departure from the winter- ing grounds and arrival on the breeding grounds, the penis of the immature, Fig. 11D, undergoes develop- ment nearly comparable to that of the adult in spring, Fig. 11E. However, the immature still possesses a large bursa, Fig. 10D, and in most cases immature tail feathers, which provide incontestable evidence that the bird is, indeed, only a 1-year-old. The maturation of the penis can be observed in a series of photographs, Fig. 12, taken in the course of an experiment on the effects of increased light and of daily injections of gonadotropic hormones on the maturation process. DISCUSSION AND SUMMARY In addition to the principal characters of age and sex discussed above, there are general clues to the age and sex of the bird being handled. For example, birds in the various age and sex classes vary con- siderably in size. In winter, the weight of an immature Branta canadensis interior averages about 1%2 pounds less than that of the adult; the weight of a yearling averages one-half pound less. Males are heavier than females by an average of nine-tenths of a pound in the immature and yearling age classes and 142 pounds in the adult age class. These differentials in weight are reflected in muscular development. With experi- ence, an operator should have a fairly accurate idea of the age and sex of a live goose simply by grasping it by the humeri. The muscles around the humeri of immatures are not fully developed and they feel stringy; those of older geese, particularly adult males, are well developed. The inexperienced can most ef- fectively learn to sex and age geese in fall and winter by using the key below: 1. Some or all tail feathers with notched, worn tips and relatively narrow vanes, Fig. 2A, B, D; color blackish Dic uirieeereyie on car neeaie mieten ict eioue aoe cc’ Siew vais 6 All tail feathers with unnotched, unworn tips and relatively broad vanes, Fig. 2C; color black...... 2. Primaries pointed at tips, Fig. 3B.............. 6 Primaries obtuse or rounded at tips, Fig. 34...... 3 Oo CIS tDLONC Mba aha etaTura iWin Sietsia eis Wisre is «// bis sia alalais.eje 6's 4 Jape} Che) cs Ak GAs Seon icaee UG nO Caer 5 4. External portion of sphincter muscle a pale flesh color; penis intermediate in size, Fig. 11B, usually a pale flesh color, translucent and smooth; bursa open and easily probed, usually to a depth of 15-20 mm; spur of each wing smooth and feathered over at tip, Oy ee ayo a an ie A ee yearling male External portion of sphincter muscle dark red or purple; penis large, Figs. 11C and 12A, dark red or purplish in color, with wrinkled surface and fairly prominent venation; bursa closed or, if open, shallow and probed with difficulty; tip of each wing spur en- larged and knobby at tip and more or less denuded OLMLentUPIS OIE OD eee hess trv hateele so oe adult male 13 5. External portion of sphincter muscle, Fig. 10A, not much larger than that of immature and light flesh- red in color; oviduct closed at juncture with cloaca; bursa open and easily probed, usually to a depth of 15-20 mm, as in yearling male...... yearling female External portion of sphincter muscle, Fig. 10B, much larger than that of either immature or yearling fe- male and dark red or blotched with purple; oviduct open and easily probed; bursa closed or, if open, shallow and probed only with difficulty. . .adult female Gn benisspresents Bugs iA rer pyeeteicesie etek immature male Penis Absentistj.,.