Mechanisms underlying parent-offspring recognition in birds have fascinated researchers for centuries. Yet, the possibility that chicks recognise parental odour at hatching has been completely overlooked, despite the fact that olfaction is one of the first sensory modalities to develop, and social chemosignals occur in avian taxa. Here we show that Zebra Finch chicks (Taeniopygia guttata) are capable of identifying parental odours at hatching. In our first experiment, chicks begged significantly longer in response to the odour of their genetic mother or father compared to the odour of a non-relative of the same sex and reproductive status. In a second experiment, we cross-fostered eggs and tested the response of hatchlings to the scent of genetic vs. foster parents. Chicks from cross-fostered eggs responded significantly more to the odour of their genetic mother than their foster mother, but exhibited no difference in response to genetic vs. foster fathers. This is the first evidence that embryonic altricial birds are capable of acquiring chemosensory knowledge of their parents during early development, and retain chemical familiarity with their genetic mother despite egg cross-fostering. Furthermore our data reveals that kin recognition in birds can develop without any association with a genetic parent at hatching.

Avian courtship behaviour is essential to attract potential mating partners. Courtship behaviours can involve displays of different sensory modes. Sex discrimination is a crucial step and in many bird species, sexes differ in acoustic and visual traits, allowing sex discrimination. It has been shown only recently that in some species of Estrildid Finches, chemical cues are involved in social communication. Here, we investigated whether olfaction also plays a role in sex discrimination in Estrildid Finches. Investigating olfactory sex preferences as an indicator behaviour in six different Estrildid Finch species, we aimed to understand whether sex- and/or species-specific differences in olfactory preferences exists and whether olfactory sex preferences correspond to species-specific differences in sex-specific acoustic and visual displays, e.g., singing, plumage dimorphisms and courtship dance. Olfactory sex preferences were tested in a Y-Maze test. We found differences in scent preferences among the different species of Estrildid Finches. We discussed the behavioural pattern with respect to other species-specific traits. And their potential implications in a broader mate choice context.