We compared incubation and fledging times between large (>2 kg) migrating and sedentary birds. We found that while length of incubation period does not differ between migrants and nonmigrants, fledging period is significantly shorter in the former. This pattern is apparent in the class as a whole, as well as within orders, families, and genera. Additional, albeit weak, evidence suggests that clutch sizes of migrants are smaller than those of closely related resident birds. We hypothesize that the need to migrate constrains the length of developmental period of large migrating birds, especially in species that undertake long-distance migration.
- Body size