Sex-dependent risk taking in the collared flycatcher, Ficedula albicollis, when exposed to a predator at the nestling stage

An increased mortality rate is a cost of parental care, and can be high during the provisioning phase of altricial nestlings. When a parent stops feeding the nestlings temporarily after seeing a predator, it can reduce its own predation risk, but the suspension of parental care may also reduce its offspring's chances of surviving. We modelled this situation by exposing a stuffed sparrowhawk near collared flycatcher nests and removing it when both parents had seen it. We measured the time (return time) between the removal and when each parent entered the nestbox. The parents' risk taking and the return time are assumed to be inversely related. We studied which brood variables the parents take into account when deciding how much risk they are willing to take during the provisioning period. Males took more risk for older and better-quality nestlings and earlier broods. The females' behaviour was opposite to that of the males: they took significantly less risk for older and better-quality offspring and visited the nestbox later for earlier broods. The males' behaviour supported the reproductive value hypothesis, that risk taking is related to brood value and survival chances, whereas the females' behaviour supported the harm to offspring hypothesis, that risk taking is related to the broods' vulnerability. (C) 2000 The Association for the Study of Animal Behaviour.