Report 163
163. Gunn A.,
J. Boulanger and J. Williams .
Calf Survival and Adult Sex Ratio in the
Bathurst Herd of Barren-Ground Caribou 2001-2004. 89 pp
Annual monitoring of calf survival is a
useful tool to help determine the trend in numbers of
barren-ground caribou (Rangifer tarandus groenlandicus).
Calf survival is an index of the potential for herd
increase. We estimated calf survival in the Bathurst herd
from classifying caribou into sex and age classes in March/
April 2001-2004 and in November 2000, 2001 and 2004. The
fall counts had the additional objective of measuring adult
sex ratio. Mean late winter calf survival and the calf-cow
ratios have declined by almost half in 2001-2004 compared
with 1985-1996. Mean calf survival rate for 2001-2004 was
0.203 (SE 0.011) compared to 0.395 (SE 0.048) for
1985-1996. Using the calf-cow ratios and estimates of
female survival (based on satellite-collared cows) allows us
to estimate that the Bathurst herd has declined since 1985.
The rate of decline (l = 0.94 SE=0.013) is similar to the
rate estimated from successive 1986-2003 surveys of breeding
females. Calf survival during the winters was almost twice
the rate estimated during the summer from birth to fall as
measured in 2000/01 and 2001/02. The proportion of bulls in
the Bathurst herd in fall 2004 was low (37%), however
similar proportions have been observed in Alaskan caribou
herds. There is a tendency for declining herds to have
lower sex ratios but it varies between herds according to
the interplay of factors affecting herd size. |
