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, 4 (4), e110

Migratory Restlessness in an Equatorial Nonmigratory Bird


Migratory Restlessness in an Equatorial Nonmigratory Bird

Barbara Helm et al. PLoS Biol.


The urge of captive birds to migrate manifests itself in seasonally occurring restlessness, termed "Zugunruhe." Key insights into migration and an endogenous basis of behavior are based on Zugunruhe of migrants but have scarcely been tested in nonmigratory birds. We recorded Zugunruhe of African stonechats, small passerine birds that defend year-round territories and have diverged from northern migrants at least 1 million years ago. We demonstrate that Zugunruhe is a regular feature of their endogenous program, one that is precisely timed by photoperiod. These results extend ideas of programs for periodic movement to include nonmigratory birds. Such programs could be activated when movements become necessary, in line with observed fast changes and high flexibility of migration. Attention to Zugunruhe of resident birds promises new insights into diverse and dynamic migration systems and enhances predictions of avian responses to global change.


Figure 1
Figure 1. Nocturnal Activity under Constant Photoperiod (Light/Dark 12.25:11.75 h)
Activity of five African stonechat males (upper panel) and four females (lower panel) recorded continuously in individual registration cages recorded for 1.5 years. Curves show nocturnal activity (Zugunruhe) as the number of 10-min intervals during which the birds were active at night. Since the birds received no temporal cues, the repeated, spontaneous outburst of nocturnal activity indicates an underlying endogenous component. Vertical gray bars indicate years.
Figure 2
Figure 2. Zugunruhe under European Day Length Conditions
Curves show mean nocturnal activity of ten resident African (upper panel, orange line) compared to 26 migrant European (lower panel, blue line) stonechats kept individually for one migration period under simulated natural European day length conditions; for details, see Figure 1.
Figure 3
Figure 3. Relationship between Onset of Zugunruhe and Hatching Date
African resident (orange dots, solid regression line; n = 10) and European migrant (blue triangles, dashed regression line; n = 26) stonechats initiated Zugunruhe at progressively younger ages when hatched late in the season under European day length conditions. Inlay: pairs of African (right) and European (left) stonechats; females are less conspicuously colored than males. Drawing is by H. Kacher.

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