Complex feeding behaviour by magpies in nests with great spotted cuckoo nestlings

Soler, Manuel; Macías-Sanchez, Elena; Martin-Galvez, David; De Neve, Liesbeth

12 July 2017

Parent decisions about food allocation are usually based on simple time-saving rules that optimize their own fitness; however, they can sometimes vary depending on the prevailing ecological conditions both outside and inside the nest. Parent-offspring interactions also become more complex when parents suffer from brood parasitism, which implies that they care for the parasite’s eggs and unrelated young. The great spotted cuckoo (Clamator glandarius) is a specialist brood parasite that uses the magpie (Pica pica) as its primary host. Here, by filming food allocation by magpie parents in natural non-parasitized and experimentally parasitized and non-parasitized magpie nests, we have found that magpie provisioning behaviour is highly complex including two types of feedings apart from normal ones. First, false feedings, when the parent touched the chick’s beak but did not leave any food, occurred more frequently when feeding a cuckoo than when feeding magpie nestlings. Second, two types of what we have called coax feedings: (2a) when magpie parents induce a nestling to beg by waking it up by touching it softly with the beak, and (2b) when parents disregard begging signals (always from brood parasitic great spotted cuckoos) while coaxing one non-begging nestling (always one of their own) to feed it. We suggest that brood parasitism, involving selfish excessively begging nestlings, could have acted as a selective pressure for both false and coax feedings to evolve, as both imply ignoring nestlings that beg too much. We also discuss that these parental responses could have evolved either by a discrimination without recognition mechanism, or, more probably, by a recognition-based discrimination mechanism.