Behavioural responses of great tits to experimental manipulation of nest temperature during incubation

Abstract

In several bird species only one member of the pair incubates the eggs. This individual should trade-off the time between caring for the eggs and leaving the nest to forage or perform other self-maintenance activities. Thus, daytime incubation is intermittent, and the number of "sessions" and "recesses", and their length, impact egg temperatures and therefore embryo development. We evaluated female investment decisions, and their reproductive consequences, by experimentally heating or cooling great tit Parus major nests during the incubation period in a Mediterranean population. Heated females were less often encountered within the nest incubating, and their recesses tended to be longer. Even though mean nest temperatures were higher in heated than in control nests, heating did not affect breeding success, size or condition of the nestlings, or parental condition or behaviour when feeding the nestlings. On the other hand, temperatures in cooled nests were lower than those in control nests during the daytime (but not during the night). However, females seemed able to compensate for the treatment, since breeding success was similar in cooled and control nests, and neither nestlings nor parents showed negative effects of the cooling treatment.