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Feeding and development of Sparrowhawk Accipiter nisus nestlings
Author(s) -
Newton I.
Publication year - 1978
Publication title -
journal of zoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.915
H-Index - 96
eISSN - 1469-7998
pISSN - 0952-8369
DOI - 10.1111/j.1469-7998.1978.tb03302.x
Subject(s) - accipiter , biology , predation , plumage , nest (protein structural motif) , hatching , zoology , kestrel , brood , competition (biology) , body weight , buzzard , ecology , biochemistry , endocrinology
At three nests of Accipiter nisus the young were brooded almost continuously for the first seven or eight days, then steadily less until days 12–15, and thereafter chiefly during rain. The male provided almost all the food for the first seven or eight clays, after which his rate of prey delivery slackened off. This coincided with increased hunting by the female and, by the late nestling stage, both parents provided about the same number of items. The numbers of prey deliveries fluctuated greatly from watch to watch, and were significantly depressed during rain. On average, males brought significantly smaller prey than females (up to 80 and 500 g respectively), and the total weight of prey brought to the nests was greater when both sexes hunted than when the male hunted alone. For the three nests, the total food consumed over 32 days from hatching was estimated at 5900 g (four young depleted to three), 5900 g (four young depleted to two) and 13,800 g (four young throughout). These widely varying estimates are all in line with previous published figures. Both sexes were hatched from eggs of similar weight, but soon diverged in growth and, before they left the nest, females were almost twice as heavy as males. No difference in food consumption was detected between the sexes but, while females achieved greater weight, males showed more rapid development of plumage and body skills, and flew about four days earlier. The more rapid development of the males is regarded as a means of alleviating competition with their larger sisters. Among the three nests, the best and most even growth among all young was associated with: (a) regular and frequent deliveries of prey items; (b) good attentiveness by the female, including almost continuous brooding in the early nestling phase, and remaining near the nest to hunt towards the end; (c) the partitioning of prey by the female until a late stage in nestling growth; and (d) when the young fed themselves, minimum aggression among them and the ready surrender of prey by one young to another. Poor, uneven growth and starvation were associated with the opposite conditions.