Diseases and accidents. — Diseases and accidents are not 
usually considered important in breeding Canada geese, 
and they were not major causes of mortality during our 
study. Nevertheless, these factors were examined at Buldir 
because of the endangered status of the goose, 
In 1975 goslings captured at Buldir to replenish captive 
stocks were heavily infested with coccidia when they arrived 
at the Patuxent Wildlife Research Center, Laural, Mary- 
land (R. Erickson, personal communication). Analysis of 
goose droppings subsequently collected at Buldir in 1975 
showed that a high percentage of the wild birds were carry- 
ing coccidia (J. Carpenter, personal communication). 
Apparently under normal conditions the birds suffer no 
detrimental effects, but under the stress conditions incurred 
during shipping, the parasitic infection overwhelmed them. 
It is not known if conditions of stress occur in the wild suffi- 
cient to induce coccidiosis. 
A female with a bare brood patch was found dead in June 
1976. Necropsy indicated the bird died from generalized 
peritonitis caused by a ruptured egg in the oviduct (L. N. 
Locke, personal communication). 
Two goslings that had apparently fallen from the slope 
above were found dead on a Buldir beach (K. W. Kenyon, 
unpublished report). In 1975 we found a dead Class Ic 
gosling with a swelling and discoloration in the area of the 
wrist. The injured bird may have died from infection. 
In 1976 we saw at least 11 geese that were either limping 
or dragging a leg in flight. We captured two recently fledged 
goslings that were either injured as a result of an accident 
or had been hit by predators. One had a broken ulna, the 
other a crippled foot. Perhaps accidents occur while goslings 
are learning to fly. We observed some possibly injurious 
landings made by fledglings during high-velocity, gusty 
winds. 
1976 Populations 
To estimate the number of Aleutian Canada goose fledg- 
lings produced at Buldir Island in 1976, we used the formula 
of Ricker (1958) — 
n= MC + UD 
R+ 1 
where N = estimate of the total population of fledg- 
lings 
M = number of goslings marked with color 
bands in 1976 (105) 
C = total number of fledged goslings seen on 
census (962) 
R = number of color-marked fledged goslings 
seen on census (197) 
and calculated that 
105 (962 + 1) 
197 + 1 
510 fledglings. 
Zz 
ll 
15 
Given an average brood size of 3.99 (Table 9), 128 breeding 
pairs produced young. Since 93% of all nesting pairs were 
successful in 1976, 138 pairs laid clutches. 
Given an April 1976 population estimate of 900 Aleutian 
Canada geese (Woolington et al. 1979), and no correction 
factor for the unknown amount of adult mortality from 
April to September, the 1976 production would have in- 
creased the number of geese to 1,410. A population esti- 
mate of 1,200 to 1,400 geese was derived from flock counts 
at Buldir during the last week of August 1976. This esti- 
mate is similar to the count of 1,280 Aleutian Canada geese, 
thought to include the entire population, made 12 Novem- 
ber 1976 in California (Springer et al. 1978), If 1,300 is 
used as the pre-migration population at Buldir, the age 
structure was 21.2% breeders, 39.5% non-breeding year- 
lings and adults, and 39.3% fledglings (Table 11). 
1977 Populations 
Using statistical sampling for the first time at Buldir, we 
estimated that 171 + 13 (confidence interval 90%) pairs 
of geese nested in 1977 (Table 12), It was not possible to 
collect data on nesting, hatching, and fledging success in 
1977, so averages from previous years were used to estimate 
production and the fall population. 
Based on the average nesting success for 1975 and 1976 
(91%) and the average fledglings per pair (3.99), 156 pairs 
(91% of 171) raised 622 fledglings in 1977. The fall popu- 
lation of geese at Buldir would have been 1,770 if the 1977 
production were added to the April 1977 population census 
in California (1,150 geese; Woolington et al. 1979). We sub- 
jectively reduced the estimate to 1,700 geese to compen- 
sate for mortality that occurred at an unknown rate from 
April to September. In spite of the suppositions used to reach 
this estimate, it seems reasonable since 1,630 was the peak 
fall 1977 Aleutian Canada goose population in California 
(Woolington et al. 1979). The age structure of the pre- 
migration population at Buldir based on these calculations 
was 19.6% breeders, 44.8% non-breeding yearlings and 
adults, and 35.6% fledglings (Table 11). 
Population Trends 
The pre-migration Aleutian Canada goose population 
was calculated to have increased 30.8% between 1976 and 
1977 (1,300 to 1,700 birds). Presumably the age structure 
also changed during the study. 
The population increase and accompanying change in 
age structure of Aleutian Canada geese is attributed to 
reduced mortality resulting from hunting closures on 
Canada geese initiated in 1975 in Aleutian Canada goose 
concentration areas in California to protect this endangered 
subspecies (Springer et al. 1978). Fledglings sustain dispro- 
portionately high mortality from hunting (Moffitt 1935; 
Chapman et al. 1969) which may explain the especially high 
increase (13.4%) in the non-breeding yearling and adult 
age categories into which the 1976 fledglings would enter 
