Birds of Indian Subcontinent

Lifetime Reproductive Output of Female Sparrowhawks

Publication Type:Journal Article
Year of Publication:1985
Authors:Newton, I
Journal:Journal of Animal Ecology
Date Published:1985
ISBN Number:00218790
Keywords:Accipiter, Accipiter nisus, Accipitridae
Abstract:(1) The number of fledglings reared in a lifetime was determined for a sample of 142 female sparrowhawks. These females were representative, in terms of longevity, of the study area population during a 13-year period. (2) They raised between zero and twenty-three young during their lives, the number varying primarily with longevity, as long-lived females in general raised more young than short-lived ones. Lifetime production was also greater in longer-winged females (assumed to reflect larger body-size), and in females that had been raised in the study areas than in those which had moved in from elsewhere. It did not vary with type of natal or breeding habitat. (3) The number of fledglings reared by individuals correlated with the number subsequently recruited to the breeding population. (4) Overall, about 23.5% of fledgling females from one generation contributed fledglings to the next. About 72% of fledglings died before they could breed, and another 4.5% attempted to breed, but did not raise young. (5) Given certain assumptions, it could be calculated that 18% of surviving females had bred by the end of their first year, 49% by the end of their second, 83% by the end of their third, and the remainder by the end of their fourth. Occasional individuals which had bred in a previous year missed one or more years in later life. Delayed breeding by the majority of females was attributed to shortage of mates or food, rather than to individuals holding back to enhance production in later life.
Short Title:Journal of Animal Ecology
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