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 dur ing the provisioning phase of altricial nestlings. When a parent stops feed ing the nestlings temporarily after seeing a predator, it can reduce its ow n predation risk, but the suspension of parental care may also reduce its o ffspring's chances of surviving. We modelled this situation by exposing a s tuffed sparrowhawk near collared flycatcher nests and removing it when both parents had seen it. We measured the time (return time) between the remova l and when each parent entered the nestbox. The parents' risk taking and th e return time are assumed to be inversely related. We studied which brood v ariables the parents take into account when deciding how much risk they are willing to take during the provisioning period. Males took more risk for o lder and better-quality nestlings and earlier broods. The females' behaviou r was opposite to that of the males: they took significantly less risk for older and better-quality offspring and visited the nestbox later for earlie r broods. The males' behaviour supported the reproductive value hypothesis, that risk taking is related to brood value and survival chances, whereas t he females' behaviour supported the harm to offspring hypothesis, that risk taking is related to the broods' vulnerability. (C) 2000 The Association f or the Study of Animal Behaviour.