S51.2: Brood parasites: The advantages of being a different species

Avian brood parasites lay their eggs in the nests of other species (hosts) which incubate and rear the brood-parasite offspring. This reproductive strategy directly reduces the cost of reproduction (e.g. parental care) and, therefore, may be subject to natural selection. I discuss three additional advantages arising from the fact that host and parasite are different species and that, therefore, adult and nestling brood parasites apparently never have contact with each other. (1) In relation to the vertical transmission of pathogens, because some pathogens are host specific, the brood-parasite nestlings have a very low probability of being infected by the specific brood-parasite pathogens. Thus they have a reduced risk of being infected by pathogens compared with other nestlings which are reared in the nest of its own species. (2) In terms of the begging behaviour of brood-parasitic nestlings, because parental care is given by other species, there does not exist both genetic relatedness between foster parents and brood parasitic nestlings, nor a genetic correlation between exaggerated begging behaviour of an individual during the nestling stage and the costs when adult from the exaggerated begging behaviour of their offspring. Consequently, the level of begging behaviour in brood-parasitic nestlings is not constrained by the parent-offspring conflict or by such a genetic correlation. (3) Finally, brood parasites could also have the advantage of selecting foster parents for their offspring according to their parental quality. Brood parasites may be able to assess both the parental quality of the host pair and the quality of its territory using sexually selected traits when considering which nest to parasitise.