title: Could a Factor That Does Not Affect Egg Recognition Influence the Decision of Rejection?
abstract: Rejection of the parasitic egg is the most important defence of hosts against brood parasites. However, this response is variable among and within species, and egg discrimination is not always followed by egg rejection. Low risk of parasitism and high risk of rejection costs may lead to the acceptance of the parasitic egg even if it has been previously recognized. The main aim of this paper is to answer a relevant question: can a single egg trait provoke the acceptance of an experimental egg previously recognized as foreign? Increased egg mass should hamper the ejection of an egg that has been discriminated because ejection of a heavy egg may imply higher rejection costs for hosts. We have tested this prediction by experimentally parasitizing natural nests of Common Blackbirds (Turdus merula) with non-mimetic model eggs of different mass (heavy, normal-weight, and light) while controlling for potential confounding factors such as egg size and colour. Our results showed that blackbirds more frequently accepted heavy eggs, even when previously recognized. This differential acceptance may be related to insufficient motivation to assume the higher costs that the ejection of a heavy egg could impose.
authors: Dept. Zoology, Facultad de Ciencias, Universidad de Granada, Granada, Spain.
authors: Francisco
authors: F
authors: Ruiz-Raya
authors: Dept. Zoology, Facultad de Ciencias, Universidad de Granada, Granada, Spain; Grupo Coevolución, Unidad Asociada al CSIC, Universidad de Granada, Granada, Spain.
authors: Manuel
authors: M
authors: Soler
authors: Dept. Zoology, Facultad de Ciencias, Universidad de Granada, Granada, Spain.
authors: Lucía Ll
authors: LL
authors: Sánchez-Pérez
authors: Dept. Zoology, Facultad de Ciencias, Universidad de Granada, Granada, Spain; Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, Groningen, The Netherlands; Dept. Wetland Ecology, Estación Biológica de Doñana, CSIC, Sevilla, Spain.
authors: Juan Diego
authors: JD
authors: Ibáñez-Álamo
mesh_terms: D000818:Animals; D003116:Color; D003163:Competitive Behavior / Q000502:physiology; D005260:Female; D006790:Host-Parasite Interactions; D009425:Nesting Behavior / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D021641:Recognition, Psychology; D020308:Songbirds / Q000502:physiology*; D015053:Zygote / Q000469:parasitology*