Within-colony spatial segregation leads to foraging behaviour variation in a seabird

Abstract

Central-place foraging in large seabird colonies leads to high levels of intra-specific competition for food resources, often resulting in between-colony spatial segregation. However, little is known about within-colony variation in foraging behaviour that may arise from breeding locations. Using little penguins Eudyptula minor from a large colony (ca. 32 000 individuals) on Phillip Island (Australia), we present a novel approach combining GPS, diving, acceleration and bathymetry data. We investigated within-colony variation in 3-dimensional distribution of prey encounters and its consequences for foraging behaviour and breeding success. Over 1 breeding season, we simultaneously tracked 63 little penguins from 2 breeding sites located ~2 km apart and monitored their breeding success. We recorded 58 452 dives, of which 11 992 had prey en - counter events associated. Results revealed strong spatial foraging segregation between sites throughout the breeding season and differences between sites in prey encounter depth during chick-rearing (mean ± SE, 11.8 ± 0.2 m vs. 17.3 ± 0.3 m). Birds from one site foraged in deeper waters and apparently experienced higher levels of competition, resulting in lower prey en - counter rates and lower foraging efficiency (i.e. body mass gain after foraging trips), hence these birds seemed less successful. However, breeding success was high (>1.5 chicks fledged per pair) at both sites, indicating that food was not a limiting factor that year. Nonetheless, breeding success records over the last 12 yr showed that the site where birds foraged at deeper depths produced fewer chicks. Our findings highlight the importance of understanding small-scale spatial segregation to capture foraging behaviour variation within large seabird colonies.