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The seasonal course and magnitude of migratory restlessness recorded in four populations of the blackcap Sylvia atricapilla differ in a population-specific fashion that is related to the distance of travel. Experimentally produced hybrids of an exclusively migratory European population and a partially migratory African population showed intermediate migratory restlessness and an intermediate percentage of birds displaying restlessness compared to the two parental stocks. These results demonstrate the genetic basis of migratory behavior in this avian species and support the hypothesis that partial migration of populations is due to polymorphism.
Berthold et al. (Fri,) studied this question.
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