![]() Akin to mammals 25, olfactory sensory neurons of domestic chicks ( Gallus gallus domesticus) are also fully functional within the egg six days prior to air-breathing 26, enabling odour learning in ovo 27. Chicks of several avian taxa can discriminate between environmental (non-social) odours at an early developmental stage 19, 20, 21, 22, 23, 24. We focused here on olfactory recognition of parental odour during ontogeny in a model altricial songbird, the Zebra Finch ( Taeniopygia guttata). Furthermore, evidence is accumulating that birds have a functioning sense of smell and make use of olfactory cues in social contexts, including sex and species discrimination 10, 11, nest 12, 13, mate 14, 15, 16, and kin recognition 17, 18. This sensory modality becomes functional in embryos prior to hearing and vision, in a pattern common to other vertebrate taxa 9. The role of chemical perception, in particular, has been notably overlooked in behavioural biology of birds 7, 8. Testing the discrimination abilities of chicks at a very early stage provides insight into the underlying mechanisms of parent recognition and potentially kin recognition. Parent-offspring recognition is therefore presumed absent at earlier developmental stages 3. However, altricial chicks do not recognize parental calls, nor do they develop individual-specific calls themselves, until shortly before fledging 3. Parent-offspring recognition is generally assumed to be based on individual-specific cues, such as vocal recognition. For example, King Penguin chicks ( Aptenodytes patagonicus) easily recognise parents from a crowd of thousands 5, whereas Common Cuckoos ( Cuculus canorus) exploit the lack of recognition of adult Reed Warblers ( Acrocephalus scirpaceus) that feed enormous cuckoo chicks 6. Studies of many avian species highlight extreme examples of both success and failure to recognize parents and offspring 2, 3, 4. Parent-offspring recognition is a fundamental aspect of parental care 1, and birds are no exception. Furthermore our data reveals that kin recognition in birds can develop without any association with a genetic parent at hatching. 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. 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. In a second experiment, we cross-fostered eggs and tested the response of hatchlings to the scent of genetic vs. 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. ![]() ![]() Here we show that Zebra Finch chicks ( Taeniopygia guttata) are capable of identifying parental odours at hatching. 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. ![]() Mechanisms underlying parent-offspring recognition in birds have fascinated researchers for centuries.
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