Behaviour 2019
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Proximate predictors of variation in egg rejection behavior by avian brood parasite hosts
Mikus Abolins-Abols, Mark Hauber. University of Illinois Urbana-Champaign, Urbana, IL, United States

The rejection of parasitic eggs by avian brood parasite hosts is one of the most effective defenses against parasitism. Despite its adaptive significance, egg rejection shows substantial inter- and intra-specific variation. Understanding variation in egg rejection requires that we study potential variation in parental motivation to care for eggs within the cognitive and sensory contexts presented by parasitized nests. Here we asked whether a suite of life-history and physiological factors explained variation in rejection of model eggs by American Robin Turdus migratorius females. The probability of egg rejection was negatively related to clutch size: females with fewer eggs were more likely to reject model eggs. In turn, females with greater mass, higher corticosterone levels, and later in incubation were less likely to reject model eggs. Proximate predictors of egg rejection behavior therefore appear to include both the components of the nest’s perceptual environment (the ratio of foreign vs. own eggs) as well as contributors to maternal motivation towards eggs (endocrine and temporal factors).