Is there a sex-specific difference between parasitic chicks in begging behaviour?

Offspring of birds and mammals demand food from their parents through an array of movements and vocalisations known collectively as begging behaviour. We explored sex-specific differences in the begging behaviour of a brood parasite, the common cuckoo (Cuculus canorus), fostered by the great reed warbler (Acrocephalus arundinaceus). As adult male parasites are larger than female parasites, we predicted that male chicks would vocalise more than female chicks. We also predicted a higher frequency of pecking in male chicks than female chicks, and in older compared to younger chicks. Pecking was considered to be any sudden attack of the parasite directed at the head or body of the hosts. Our observations confirmed that there were no sex-specific differences in nestling begging vocalisation and that older chicks tended to deliver more pecks at their hosts than younger ones. One explanation for the lack of intersexual differences in begging vocalisation is that the common cuckoo is an evictor parasite which does not need to compete for food. Alternatively, both male and female cuckoos might already beg at their maximum intensity or have similar food requirements. Moreover, the pecking behaviour in older nestlings could be a strategy to obtain more food from hosts without increasing host-present begging vocalisation.