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 
