GROWTH AND ALLOCATION IN CAPTIVE COMMON MURRE (URIA AALGE) CHICKS

Abstract

A.-In birds, relative growth rates of morphological characters change in response to restricted food intake during development. Diff erential allocation of limited resources is hypothesized to refl ect functional priorities for developing chicks. Body mass, wing, and fl ight feathers have been identifi ed as potential priorities for seabird chicks. We used allometry to examine allocation in captive Common Murre chicks fed within a range of natural provisioning. During days 10-45 post-hatch, chicks were fed one of four diets that varied in biomass, energy content, and composition. Energy intake had a more profound eff ect on growth and development than diet composition; it signifi cantly reduced absolute growth of body mass, manus, and tarsus. Between day 15 and day 20, allocation changed in all treatments: growth of manus was maintained at the expense of body mass. Chicks in more restricted treatments shi ed allocation to manus at a lower body mass than those in less restricted groups, but subsequently allocated similarly. Wing loading was higher for chicks than for adult alcids, but scaled similarly. Growth of primary feathers was the most sensitive to small diff erences in diet composition. Our data also suggest that some changes in allocation may be ontogenetically determined rather than part of an adaptive response to reduced food intake.