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Relations between Number in Brood, Feeding-Rate and Nestling Period in Nine Species of Birds in Tanganyika Territory

R. E. Moreau
Journal of Animal Ecology
Vol. 16, No. 2 (Nov., 1947), pp. 205-209
DOI: 10.2307/1495
Stable URL: http://www.jstor.org/stable/1495
Page Count: 5
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Abstract

1. Feeding-rates for four species of hirundine, three of swift, one of paradise flycatcher and one of wagtail, derived from about 5000 hr. of observations at 102 nests in Tanganyika Territory, are summarized. Additional nestling periods are available, making in all about 500 for these species. 2. In most of the species for which there is a good volume of data, feeding-rate per nestling varies greatly both from day to day in some of the nests and as between nests (calculated on the mean of all the data available for each). In several species ranges in feeding-rate per nestling for different numbers-in-brood overlap widely. As a rule, the more young in the nest the more frequent the parents' visits, but not in proportion to the increase in the number of young; so that on the average a solitary nestling gets more food than a member of a pair or of a trio. Two species for which there is, as it happens, the biggest volume of data, are however to some extent exceptions: there is practically no difference (a) in the white-rumped swift (Micropus caffer struebelii) between the feeding-rate of a solitary young bird and that of a member of a pair, (b) in the red-throated rock-martin (Ptyonoprogne fuligula rufigula) between members of a pair and members of a trio. 3. There is no evidence that higher feeding-rate is correlated with shorter nestling period in any species but the paradise flycatcher (Tchitrea perspicillata ungujaensis), where there is only an isolated observation. 4. On correlation between feeding-rate and nestling period of individual young the data do not suffice for statistical examination, but inspection of detailed records (not here reproduced) gives no satisfactory indication that lower feeding-rate is correlated with longer nestling period. In three species nestling periods are recorded for many nests in addition to those for which feeding-rates are available. They show no statistically significant difference between the nestling periods of solitaries and pairs in the white-rumped swift (where there is no difference in the feeding-rates) and none in the palm-swift (Cypsiurus parvus myochrous) (where there is a difference in the feeding-rates). But in the rock-martin the nestling period averages 1.5 days longer (a significant difference) in trios than in pairs, though there seems to be no difference in the feeding-rates. 5. Apart from this last anomalous result, the general conclusion drawn from this study is that the greater the number in brood the less food each is likely to receive and, since nestling period is not prolonged in proportion to drop in feeding-rate, the less the individual is likely to weigh when it leaves the nest.

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