Effects of distance to wintering area on arrival data and breeding performance in great cormorants Phalacrocorax carbo

Abstract

Great Cormorants Phalacrocorax carbo sinensis breeding in the same colony often vary markedly in where they winter and in their date of arrival. The main aim of this study was to explore whether date of arrival, fledgling production and lifetime reproductive success were related to the distance migrated in spring. Based on resightings and dead recoveries of colour-ringed birds we identified the approximate wintering area for 195 breeding males and 179 breeding females. Based on daily searches for colour-ringed individuals in the study colony we found timing of arrival to vary by up to 1.5 months for a given distance to the wintering area. Males and females wintering 300 km from the colony. For breeders wintering 601–2500 km from the colony, date of arrival was only weakly related to distance from the colony, probably because of an earlier onset of spring migration from the most southern wintering areas, allowing these individuals to catch up with birds wintering further north. Mean fledgling production per individual did not decrease with increasing distance to the wintering area. However, lifetime reproductive success of males wintering 301–900 km from the colony was lower than among males wintering closer to or further from the colony. These birds had fewer breeding seasons, suggesting that wintering at intermediate distances was a poor strategy for males. Females that arrived early and were presumed to winter locally had more breeding seasons and thus higher lifetime reproductive success than migrating females. We found that in this population long-distance migrants do not arrive later, do not breed with lower success or less frequently than those wintering at intermediate distances from the colony