Consistency and plasticity of risk-taking behaviour towards humans at the nest in urban and forest great tits, Parus major

Urban animals often show bolder behaviour towards humans than their nonurban conspecifics. However, it is unclear to what extent this difference is due to consistent individual characteristics or to plasticity such as habituation. To address this question, we investigated parental risk-taking behaviour in 371 female great tits in urban and forest populations by checking their nest repeatedly (several times per week, for up to nine breeding episodes) and recording their behavioural responses to this recurring disturbance during incubation. We found that urban females were bolder, as they stayed on the nest more often than females in forests. Furthermore, great tits produced alarm calls around the nests more frequently in urban than in forest habitats. There was no habitat difference in the frequency of an antipredator behaviour, the hissing threat display on the nest, although this was rare in both habitats. We also tested the consistency and plasticity of risk-taking behaviour on three different temporal scales (within breeding attempts, between broods within a year and across years). Staying on the nest was highly repeatable within females, whereas alarm calls had low repeatability within pairs at all three temporal scales. The probability of staying on the nest increased within breeding attempts, whereas the probability of alarm calls increased across years. Neither consistency nor plasticity in these components of risk taking differed between urban and forest habitats. We conclude that urban birds are bolder in multiple behavioural measures and, overall, both stable individual differences and behavioural plasticity may have contributed to the higher risk taking we often see in urban populations. Furthermore, staying on the nest appears to be an individually consistent trait in female great tits regardless of habitat urbanization, providing a low-impact measurement of risk taking, which may potentially facilitate field studies related to individual differences in behaviour.