Large-scale breeding programmes for captive migratory birds have revealed much about the genetic control and inheritance of different aspects of migration behaviour, whether timing, duration or directional preferences (Berthold 1996). The most convincing results have come from cross-breeding individuals of the same species but drawn from populations with different migratory behaviour (Chapter 20). In general, the resulting offspring showed migratory behaviour that was intermediate in timing, direction and duration between their two parents. By selecting and breeding only from the most migratory individuals in a population, migratory behaviour could be enhanced over several generations, and similarly by selecting the least migratory individuals, populations became increasingly non-migratory. These experiments, conducted mainly on Blackcaps Sylvia atri-capilla, confirmed that all major aspects of migratory behaviour were genetically controlled, and could be altered by selection (Chapter 20).
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