Effects of predation risk on behaviour during breeding by two species of passerines

In response to perceived risk of predation, many animals reduce their level of activity presumably so that they are less likely to be detected, and therefore killed, by a predator. Such behavioural flexibility has been reported for a variety of species but has primarily been studied in the context of foraging decisions during non-reproductive life stages. My general objective was to examine activity patterns by two species of passerine birds during both the incubation and brood-rearing stages of breeding to determine if perceived predation risk elicited a reduction in activity levels as it does with other animals during non-reproductive periods. I found that behavioural changes exhibited by both species were dependent on the study species, predator type, and stage of breeding. Mountain bluebird (Sialia currucoides) males did not alter rates of female incubation provisioning in the presence of either hawk or squirrel predators. Both female bluebirds and tree swallows (Tachycineta bicolor) increased activity when presented with models of squirrels during incubation. Female bluebirds increased activity levels when presented with hawk models, while swallows either decreased or did not alter their activity levels during incubation. Bluebirds did not alter the rates at which they provisioned chicks when presented with models of either predator. Swallows reduced chick-provisioning rates during both predator trials but displayed a more intense response to the hawk. My results support the general theory about how prey species should respond to perceived predation risk; specifically the prediction that activity levels are altered in the presence of a predator. Altered activity levels of parents in my population presumably reflect the tradeoff between the need for self-preservation versus protecting current reproductive output. In general, my results suggest that behaviours increasing the likelihood of self-preservation were chosen more frequently.