The effects of trapping on the perception, and trade-off, of risks in the Great Tit Parus major

Great Tits Parus major and other small birds at temperate latitudes insure against overnight starvation in winter by building up a fat reserve each day, which is then depleted over night. Because this may increase their risk of predation, the levels of fat reserves carried appear to be set by the perceived balance of predation and starvation risks. This implies that the birds continuously monitor this balance of risks. Theoretical considerations for the Great Tit suggest that predation risk should decline, while starvation risk increases, through the day. Here I describe within-day changes in mass and fat reserves of retrapped Great Tits, which show that they respond to capture (perhaps because the birds perceive this as an increased risk of predation) in a manner consistent with the changing diurnal balance of predation and starvation risks. These observations have important implications for any consideration of the effect of trapping on body condition in the context of bird welfare

Gosler A.G., ARDEA 89 (1): 75-84