Different means to the same end: Long-distance migrant seabirds from two colonies differ in behaviour, despite common wintering grounds

摘要

Although seabirds that are trans-equatorial migrants show apparently broad overlap among populations in the nonbreedingseason, such large-scale pattern may conceal subtle but nevertheless key differences in migratory behaviour.These specializations could reflect adaptation to different environments during the breeding season, carry-over effects fromthe breeding to the nonbreeding period, or asymmetries in competitive ability of birds of different origin. We compared themigratory and wintering behaviour of Cory’s shearwaters Calonectris diomedea nesting in Berlengas and in the Selvagens,two colonies in contrasting oceanographic environments, separated by ca. 1200 km. Although no differences were found inwinter distribution, there was a marked divergence in timing, route and the use of staging areas during the postbreeding(autumn) migration. Birds from Berlengas typically travelled to oceanic waters in the North Atlantic for an extendedstopover, whereas those from Selvagens rarely did so. In the South Atlantic, birds from Selvagens spent more time in flight,perhaps because they had higher energy and nutrient requirements for feather replacement compared to birds fromBerlengas, which moult more flight feathers during breeding. Stable isotope analyses of feathers suggested that thisvariation in activity patterns was unrelated to trophic ecology. Differences in migration routes and stopovers may exposepopulations to distinct threats, and should be taken into consideration when defining units for conservation purposes anddeveloping appropriate management strategies.