COMPARISON OF CAPELIN MALLOTUS VILLOSUS IN THE PREY LOADS OF COMMON MURRES URIA AALGE AND NORTHERN GANNETS MORUS BASSANUS FORAGING FROM THE SAME BREEDING SITEIN THE NORTHWEST ATLANTIC

摘要

Forage fishes often play key roles in the food web dynamics of top predators (Cury et al. 2012), especially in marine systems in which a diversity of large predators prey on focal forage species (Bakun 2006). In such circumstances, different seabird predators often focus on different age classes, sexes or densities of prey (Piatt 1990, Davoren & Montevecchi 2003, Frederiksen et al. 2006).During the energy-demanding chick-rearing period, seabird parents are constrained by foraging from, and returning to, the breeding site — a situation referred to as Central Place Foraging (CPF; Orians & Pearson 1979). Under the constraints of CPF, parents are assumed to select prey that provide the most nutrients for offspring with the greatest efficiency (Kamil et al. 1987, Burke & Montevecchi, 2009). The pressure for prey selectivity and efficient parental foraging is considered to be most intense among single-prey-loaders, i.e. species that deliver an individual prey item to offspring following a foraging trip (Orians & Pearson 1979). By contrast, species in which parents capture and carry multi-prey loads to chicks are expected to experience lessstringent pressure for selecting individual prey when rearing offspring (Burke & Montevecchi, 2008).