Recent breeding experience improves egg ejection behaviour

Abstract

Recognizing ones own eggs is crucial for birds, especially for hosts of brood parasites that must identify and reject different-looking parasitic eggs. While birds seem to possess a template image of their eggs, whether it is innate or learnt remains unclear. We addressed this question by experimentally inserting either artificial mimetic eggs (ME) or non-mimetic eggs (NME) into the nests of barn swallows (Hirundo rustica) during pre-laying stage. Our individually marked population allowed a unique comparison between naive first-time breeders and experienced females, as well as females with old (from a previous season) and recent (from the previous breeding attempt within the same season) experience allowing to investigate the role of memory. We found that both naive and experienced females ejected ME and NME at similar rates, indicating that the template image is neither innate nor learnt and does not play a primary role in egg recognition. Instead, our findings suggest that awareness of own egg-laying is the crucial mechanism at play, and may facilitate nest sanitation behaviour. Finally, we provide the first evidence that this mechanism improves with recent breeding experience. Future studies should investigate the role of non-visual factors that may modulate nest sanitation, such as endocrine regulation.