The first evidence of olfactory egg recognition in birds came from a study of magpies ( Pica pica).
One potential mechanism for egg recognition that has so far received little attention is the use of olfactory cues. Such potential intraspecific variation, however, referred mostly to egg colouration or spotting patterns. In addition, intraspecific variation in the appearance of eggs is generally supposed to be lower than interspecific variation, and discriminating own from conspecific eggs should thus be even more challenging. Therefore, the selection pressure of recognising CBP is assumed to be lower. The cost of raising a conspecific chick within the own brood is likely to be smaller compared to the potential fatal consequences of being the host of evicting interspecific brood parasites. Colonial-breeding species are most vulnerable to CBP because a high density of nests offers a greater opportunity for CBP and facilitates the correct timing of egg laying. However, at least 234 species show conspecific brood parasitism, and this number is likely to be an underestimation. Īlthough much emphasis has been placed on understanding the mechanisms by which hosts recognise interspecific brood parasites, less effort has been directed towards understanding if and how parents recognise conspecific brood parasitism (CBP). However, birds are faced not only with interspecific brood parasites, such as cuckoos and cowbirds, but also with conspecific brood parasites, which Davies describes as “cheating on your own kind”. Interspecific brood parasitism is probably the most prominent and obvious example in which individuals of some species seem to have failed to exhibit a recognition mechanism. Accordingly, selection should have favoured mechanisms in adults to discriminate between own and foreign offspring. Because parental care is costly in terms of time and energy, it should be provided exclusively to descendent young. Raising offspring until independence is one of the major challenges in species with parental care. The finding that females are capable to smell their own egg may inspire more research on the potential of olfaction involved in egg recognition, especially in cases where visual cues might be limited. However, shortly before hatching, females preferred significantly the odour of their own egg. After the onset of incubation, females chose randomly and showed no sign of discrimination. In a binary choice experiment, female zebra finches were given the choice between the scent of their own and a conspecific egg. without any spotting pattern, and intraspecific brood parasitism frequently occurs. Zebra finches are colonial-breeding songbirds. Here, we investigated whether female zebra finches ( Taeniopygia guttata) are able to discriminate between their own and a conspecific egg based on olfactory cues alone. However, olfactory egg recognition has almost been completely ignored. In birds, much emphasis has been placed on understanding the visual mechanisms underlying egg recognition. Therefore selection should favour mechanisms to discriminate between own and foreign offspring. Parental investment in unrelated offspring seems maladaptive from an evolutionary perspective, due to the costs of energy and resources that cannot be invested in related offspring at the same time.
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