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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Does the proportion of arthropods versus fruit in the diet influence overwintering condition of an omnivorous songbird? (2017)
Auteurs :	Emily A. McKinnon, Auteur ; T. Kurt Kyser, Auteur ; Bridget J. M. Stutchbury, Auteur
Type de document :	Article
Dans :	Journal of Field Ornithology (88(1) March, 2017)
Article en page(s) :	65-79
Langues:	Anglais
Mots-clés:	Seasonality ; delta-13-C ; delta-15-N ; dietary mixing model ; non-breeding season ; trophic ecology ; tropical forest
Résumé :	Many migratory songbirds switch from a primarily insectivorous diet during the breeding season to either a mixed diet or fruit diet during the non-breeding season. However, for species with mixed diets, arthropods may be superior food items because of their higher protein content and easier digestibility. We tested this hypothesis by analyzing the diet and body condition of omnivorous Wood Thrushes (Hylocichla mustelina) at a non-breeding site in tropical forest in Belize, Central America. We used analysis of stable isotopes δ15N and δ13C in the blood to measure diet. Our objective was to determine if a higher dietary proportion of arthropods relative to fruit (i.e., higher δ15N and δ13C) was associated with better body condition. We also examined the possible effect of age, sex, and habitat type on Wood Thrush diets, as well as any changes in diet through the overwintering period. We used a hierarchical Bayesian mixing model (MixSIAR) to estimate the proportion of different prey items in the diet of overwintering Wood Thrushes overall, in each habitat type, and over time during the non-breeding period. From January to April, we found a significant decline in δ15N in forest habitats, whereas δ15N increased in scrub habitat. There was no significant seasonal change in δ13C. Birds with higher δ15N or δ13C values were not in better body condition. Females in dry-scrub habitat consumed more fruit than males, but this did not affect body condition. Mixing model results indicated that most Wood Thrushes at our study sites consumed primarily arthropods, even during the driest times of the non-breeding season and in the driest habitat. Overall, our results suggest that the diet of Wood Thrushes varies with habitat and during the overwintering period, but diet alone was not a predictor of body condition. Wood Thrushes, and possibly other omnivorous migratory songbirds, are apparently flexibly able to meet their wintering and pre-migration nutritional demands with a variety of diets.
En ligne :	http://onlinelibrary.wiley.com/doi/10.1111/jofo.12187/abstract

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