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Comparison of optimal foraging versus life‐history decisions during nestling care in L incoln's S parrows M elospiza lincolnii through stable isotope analysis
Author(s) -
Beaulieu Michael,
Sockman Keith W.
Publication year - 2014
Publication title -
ibis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 80
eISSN - 1474-919X
pISSN - 0019-1019
DOI - 10.1111/ibi.12146
Subject(s) - foraging , offspring , predation , biology , paternal care , zoology , predator , ecology , reproductive success , habitat , demography , pregnancy , population , genetics , sociology
In short‐lived species, parents are expected to favour their offspring and may therefore have to sacrifice the best part of their diet to feed their young (‘conflict hypothesis’). In addition, they need to maximize energy delivered per unit of time to the young (‘delivery hypothesis’). We examined the influence of these two factors on food allocation in L incoln's S parrows M elospiza lincolnii by measuring plasma δ 15 N and δ 13 C values in both parents and offspring. Adults’ isotopic values were unchanged when feeding chicks, but their δ 15 N values were higher than those of their chicks. Using the isotopic signature of Lincoln's Sparrows and that of prey available in their habitat, we reconstructed the diet of parents and chicks using mixing models for stable isotope analyses. The main difference between the diet of chicks and that of adults was that the proportion of spiders was lower in chicks than in adults, while the proportion of grasshoppers was higher. Spiders appear more valuable than grasshoppers, as they are more easily digested and richer in lipids, proteins and essential amino acids. However, grasshoppers are larger than spiders and are therefore likely to be better suited to maximize energy delivery to chicks. As parents keep their diet constant when breeding and as the contribution of large prey is higher in the diet of chicks than in that of their parents, our results suggest that the influence of optimal foraging strategy is predominant over the influence of parent–offspring conflict on food allocation in L incoln's S parrows, thereby supporting our delivery hypothesis. However, this relative influence may differ when resource availability constrainsing parent–offspring conflict varies.