MICROEVOLUTIONARY ASPECTS OF BIRD MIGRATION BASED ON EXPERIMENTAL RESULTS

In many parts of the world we observe conspicuous changes in avian mig ratory habits. Alterations in migratoriness, mainly reductions, change s of migration times (particularly, later departures from and earlier returns to breeding grounds), and developments of novel migration rout es and wintering areas are most obvious. It is likely that many of the se changes are based on microevolutionary processes, i.e., selection. In a songbird population the rapid microevolution of a shift in the mi gratory direction of at least 30 degrees within 30 years was establish ed experimentally. With respect to changes in migratoriness, selection experiments with partial migrants show that shifts from full migrator iness to almost complete sedentariness are possible within 10 generati ons. Heritability estimates and other data also suggest rapid microevo lutionary changes in migration distances and periods.