Migratory restlessness in captive individuals predicts actual departure in the wild

Abstract

In captivity, migratory birds show increased activity during the time that they would normally migrate. The phenology and intensity of such 'migratory restlessness' has been shown to mirror species- and population-specific migration patterns observed in the wild and has consequently been used as a proxy for the motivation to migrate. Many studies doing so, however, were aiming to explain among-individual variation in migratory behaviour or traits, and not species- or population-specific traits. These studies thus assumed that, also at the level of the individual, migratory restlessness is an accurate proxy for the motivation to migrate. We tested this assumption for the first time and found that it holds; individuals showing very little migratory restlessness remained at stopover for longer than one night, whereas most individuals showing more restlessness departed sooner. This finding validates the use of migratory restlessness as a proxy for the motivation to migrate, thereby justifying the conclusions made in a large body of research on avian migration.

Keywords: Zugunruhe; migratory restlessness; proxy; radio-telemetry; stopover.

Figure 1.

The relationship between nocturnal migratory restlessness and the number of nights birds stayed on Helgoland after release. Migratory restlessness was defined as the number of 15 min periods between 1 and 5.5 h after lights off, during which a bird showed at least five activity counts (n = 20).