Estimates of survival in the cape vulture gyps coprotheres

Piper, S.E.; Mundy, P.J.; Ledger, J.A.

Journal of Animal Ecology 50(3): 815-826

1981


ISSN/ISBN: 0021-8790
DOI: 10.2307/4139
Accession: 005386067

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Abstract
At least 4400 nestlings of the Cape vulture G. coprotheres (Forster) were ringed from 1948-1975. Of the 135 fledged birds recovered up to Nov. 30th 1976, 118 were used to estimate survival. Four techniques were used, 2 providing unitary (i.e., average) estimates and 2 providing age-specific estimates of survival rates. Attention was paid to the assumptions upon which the analytical models were based and it was shown that the effect of the heterogeneities in the data was to underestimate survival. The average annual survival (across all age-classes) was estimated at 35-45%. First year birds had the lowest survival rate (17%) and the rate increased to 74% for 3rd yr and older birds. The estimates had very wide confidence limits, those for 1st yr birds being the widest. The probability of a fledgling reaching its 3rd yr was estimated at 10.6%. In view of the demographic importance of the parameter of juvenile survival, both study and conservation are recommended for this youngest age-class. The ringing/recovery experiment is inappropriate for mobile birds such as vultures, unless combined with an intensive color-ringing and resighting program.