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. 
