title: Naïve hosts of avian brood parasites accept foreign eggs, whereas older hosts fine-tune foreign egg discrimination during laying.
abstract: BACKGROUND
  Many potential hosts of social parasites recognize and reject foreign intruders, and reduce or altogether escape the negative impacts of parasitism. The ontogenetic basis of whether and how avian hosts recognize their own and the brood parasitic eggs remains unclear. By repeatedly parasitizing the same hosts with a consistent parasitic egg type, and contrasting the responses of naïve and older breeders, we studied ontogenetic plasticity in the rejection of foreign eggs by the great reed warbler (Acrocephalus arundinaceus), a host species of the common cuckoo (Cuculus canorus).
  
  
  RESULTS
  In response to experimental parasitism before the onset of laying, first time breeding hosts showed almost no egg ejection, compared to higher rates of ejection in older breeders. Young birds continued to accept foreign eggs when they were subjected to repeated parasitism, whereas older birds showed even higher ejection rates later in the same laying cycle.
  
  
  CONCLUSIONS
  Our results are consistent with the hypotheses that (i) naïve hosts need to see and learn the appearance of their own eggs to discriminate and reject foreign eggs, whereas (ii) experienced breeders possess a recognition template of their own eggs and reject parasitic eggs even without having to see their own eggs. However, we cannot exclude the possibility that other external cues and internal processes, accumulated simply with increasing age, may also modify age-specific patterns in egg rejection (e.g. more sightings of the cuckoo by older breeders). Future research should specifically track the potential role of learning in responses of individual hosts between first and subsequent breeding attempts by testing whether imprinting on a parasitized clutch reduces the rates of rejecting foreign eggs in subsequent parasitized clutches.
authors.affiliation: MTA-ELTE-MTM Ecology Research Group, c/o Biological Institute, Eötvös Lóránd University, Pázmány Péter sétány 1/C., H-1117 Budapest, Hungary and Hungarian Natural History Museum, Baross u. 13, Budapest H-1088, Hungary.
authors.forename: Csaba
authors.initials: C
authors.lastname: Moskát
authors.affiliation: MTA-DE "Lendület" Behavioural Ecology Research Group, Department of Evolutionary Zoology, University of Debrecen, Debrecen 4010, Hungary.
authors.forename: Miklós
authors.initials: M
authors.lastname: Bán
authors.affiliation: Department of Psychology, Hunter College and the Graduate Center of the City University of New York, 695 Park Avenue, New York, NY 10065, USA.
authors.forename: Márk E
authors.initials: ME
authors.lastname: Hauber
keywords: Adaptation; Brood parasitism; Clutch learning; Egg discrimination