Behavioural and corticosterone responses to capture and confinement of wild blackbirds (Turdus merula)

Capture and temporary confinement of wild birds are integral parts of wildlife management practice and research used, for example, during translocation or reintroduction initiatives. We report here on the behavioural and stress hormone (corticosterone) responses of wild blackbirds (Turdus merula) to capture and short-term confinement, partly consistent with some translocation protocols. We examine also the relationship between behaviour and plasma corticosterone concentrations. Acute capture induced responses in corticosterone concentration, integrated over 60 min, at the commencement and conclusion of a 22-day confinement in aviaries were similar at 669.1 +/- 66.6 (mean +/- S.E.) and 678.2 +/- 115.8 ng/mL/min respectively. However, base levels of corticosterone were higher at final release than at initial capture (6.8 and 2.2 ng/mL respectively, P < 0.001). This may reflect that the 3-week period of confinement is a chronic stressor. There was an increased propensity for locomotory behaviours (P = 0.001), maintenance behaviours (P = 0.032) and alarm vocalisations (P = 0.04) over the period of captivity. The frequency of alert behaviours (P < 0.001) decreased, probably related to habituation to captivity and possibly an associated decrease in perceived predation or starvation risk. Individual behavioural responses were generally repeatable across all observation days, with locomotory behaviours showing the highest repeatability (Repeatability = 0.592 +/- 0.084, P < 0.0001). Significant repeatabilities were also detected for corticosterone concentrations measured at 60 min after capture (Repeatability = 0.619 +/- 0.166, P = 0.0007) and corrected integrated corticosterone (Repeatability = 0.368 +/- 0.166, P = 0.039) measured on initial capture and on release. We used principle component analysis to generate a composite measure of locomotory, alert and vocalisation behaviours. This measure was positively correlated with corrected integrated corticosterone response at release (P = 0.019) when behaviour was summed across all observation days. Corrected integrated corticosterone response at initial capture (P = 0.049) was also correlated with this behavioural measure at 20 days after capture. This, in combination with the consistency in the behavioural and corticosterone responses across the period of captivity, may reflect individual differences in coping abilities to confinement that may ultimately predict post-translocation survival. (C) 2011 Elsevier B.V. All rights reserved.