Manx Shearwater Chicks: Seasonal, Parental, and Genetic Influences on the Chick's Age and Weight at Fledging

Abstract

Manx Shearwater (Puffinus puffinus) pairs on Skokholm Island, Wales, typically breed together over several seasons, rearing one chick per year. There is a seasonal decline of chick fledging weight. Even after correction for this decline, pairs tend to rear chicks that are consistently heavier or lighter than predicted on the basis of the chick's hatching date. These deviations may reflect pair quality. Weight and hatching date of a chick are not correlated with age of fledging. However, fledging ages of full siblings show significantly less variation than those of nonsiblings. The character appears highly heritable, with a heritability value around 0.84. This is the first study to address the extent to which the fledging age of wild birds is genetically determined.