PREDATOR AVOIDANCE IN NIGHT-FEEDING DUNLINS CALIDRIS-ALPINA - A MATTER OF CONCEALMENT

The anti-predator behaviour of night-feeding Dunlins Calidris alpina was studied on a tidal flat in the Danish Wadden Sea. The observations indicated that Dunlins at night depress vocalization compared with day-feeding birds. Moreover, when Dunlins were approached by a raptor during day-time almost all took flight. In contrast, when Dunlins were disturbed at night only about 60% took flight, while most of the remaining birds froze. It is suggested that depressed vocalization and freezing at night are means to escape detection by owls. How the behavioural dichotomy (freezing and escape) during nocturnal disturbance is accomplished and how it affects the spacing behaviour of night-feeding Dunlins are discussed.