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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Resident but not transient Eurasian Siskins reduce body mass in response to increasing predation risk: a natural experiment (2015)
Titre original:	Resident but not transient Eurasian Siskins reduce body mass in response to increasing predation risk
Auteurs :	Jordi Pascual, Auteur ; Juan Carlos Senar, Auteur
Type de document :	Article
Dans :	Journal of Ornithology (156(2) 2015/01/13)
Article en page(s) :	451-456
Langues:	Anglais
Résumé :	The body mass of birds is the result of a trade-off between predation and starvation risks. According to the mass-dependent predation hypothesis, birds reduce their body mass when predation risk increases. Many studies have supported this hypothesis, but it has rarely been possible to investigate the mass-dependent predation risk response by comparing individuals of the same species foraging simultaneously at the same location, in the field and facing a real (not simulated) risk of predation. Wintering Siskins (Carduelis spinus) are divided in two subpopulations: residents, which stay in a foraging area for several weeks or months, and transients, which only remain a few hours or days. In this paper, we present a natural experiment by comparing the body mass variation of resident and transient Siskins between a period of the wintering season without avian predators and another period with a Sparrowhawk (Accipiter nisus) that was hunting regularly. We found that resident Siskins reduced their body mass with the presence of the hawk, while transients did not. Since in a previous study with no avian predators at the study area it was found that the difference in body condition between residents and transients did not vary throughout the wintering season, we can confidently say that the reduction in body mass observed in this study was directly linked to the presence of the hawk. We additionally found that this reduction was not associated with the dominance of residents over transients. We discuss the advantages of residence related to the knowledge of actual predation risk. Our results strongly support the mass-dependent predation hypothesis.
En ligne :	http://link.springer.com/article/10.1007/s10336-014-1143-8

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