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Determinants and Consequences of Nestling Condition in Song Sparrows

Wesley Hochachka and James N.M. Smith
Journal of Animal Ecology
Vol. 60, No. 3 (Oct., 1991), pp. 995-1008
DOI: 10.2307/5427
Stable URL: http://www.jstor.org/stable/5427
Page Count: 14
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Determinants and Consequences of Nestling Condition in Song Sparrows
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Abstract

(1) We examined the relationship between nutritional condition of nestlings and their subsequent survival in the population of song sparrows (Melospiza melodia) on Mandarte Island, B.C., Canada. Nestlings in higher condition had higher survival to independence from parental care. However, survival from independence to recruitment into the breeding population was not related to nestling condition. (2) We tested whether high nestling condition was sporadically advantageous as a buffer against unpredictable food shortages, or whether high nestling condition was always advantageous. Also tested was whether increasing nutrient stores or increasing structural size were more important to nestlings. (3) Nestlings in higher nutritional condition had higher survival in 7 of 8 years. The response of nestlings to supplemental food was to grow structurally larger, and not to produce a nutrient store. (4) Comparing nestlings from first and second broods, we found that parents did not consistently produce offspring of above or below average condition. (5) Variation in nestling condition in relation to brood size would result in only a 6% difference in average survival of offspring between largest and smallest broods. Brood-size-related variation in nestling condition appears unimportant in determining optimal brood size. (6) Of those offspring that survived to independence, males had been in better condition as nestlings than had females.

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