(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. 
