Summary: | Understanding variation among individuals, populations, and species provides insight into sensitivity to change. The goal of this thesis was to examine individual specialization, niche partitioning, and phenotypic plasticity in two seabirds, the common murre (Uria aalge) and razorbill (Alca torda) breeding in northeastern Newfoundland. Using GPS tracking and stable isotopes, we examined individual- and population-level foraging ecology in relation to changing prey availability. For common murres, we found high within-individual variation in foraging trips and low spatial overlap, indicative of flexible behavior, contrasting a degree of dietary consistency. At the population level, murres and razorbills exhibited spatial segregation and divergent dive characteristics, contrasting high dietary overlap. As prey availability shifted, individuals exhibited reduced energy costs with dietary and behavioral plasticity to exploit highly available prey. Together, these findings support flexible foraging strategies for both species and provide insight into how individuals and populations interact and respond to environmental variation. February 2019
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