Comparison of optimal foraging versus life‐history decisions during nestling care in Lincoln's Sparrows Melospiza lincolnii through stable isotope analysis

• Published in: Ibis (London, England) Vol. 156; no. 2; pp. 424 - 432
• Main Authors: Beaulieu, Michael, Sockman, Keith W, Butler, Simon
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Science Pub 01.04.2014; Blackwell Publishing Ltd; Blackwell
• Subjects: adults; Animal and plant ecology; Animal populations; Animal reproduction; Animal, plant and microbial ecology; Animals; Araneae; Autoecology; Aves; Biological and medical sciences; Birds; breeding; chicks; diet; energy; essential amino acids; food provisioning; foraging; Foraging behavior; Fundamental and applied biological sciences. Psychology; grasshoppers; habitats; Life cycles; lipids; parental care; parents; progeny; proteins; resource allocation; SIAR; stable isotopes; statistical models; Vertebrata; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution; Isotopic analysis; Vertebrata; Life history; Aves; Nestling; Optimal foraging; Decision
• ISSN: 0019-1019; 1474-919X
• DOI: 10.1111/ibi.12146

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 Lincoln's Sparrows Melospiza lincolnii by measuring plasma δ¹⁵N and δ¹³C values in both parents and offspring. Adults’ isotopic values were unchanged when feeding chicks, but their δ¹⁵N 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 Lincoln's Sparrows, thereby supporting our delivery hypothesis. However, this relative influence may differ when resource availability constrainsing parent–offspring conflict varies.