Nearest neighbors as foraging cues: information transfer in a patchy environment

To assess the importance of both conspecifics and heterospecifics as cues to prey location, we analyzed patterns of seabird species co-occurrence along shipboard transects conducted near South Georgia (55degreesS, 35degreesW) during the austral summer. Using data collected over 9 d and 1500 km ocean, we focused on the behavior of 4 seabird species that are abundant in Antarctic waters: black-browed albatross Thalassarche melanophrys, white-chinned petrel Procellaria aequinoctialis, prion Pachyptila spp., and diving petrel Pelecanoides spp. We identified and recorded the behavior of the nearest neighbors of focal, flying individuals and demonstrated strong intraspecific associations for all 4 species. More conspecific neighbors of prions and diving petrels were also observed flying than expected due to chance. This result suggests that these birds may forage co-operatively with conspecifics. In contrast, more heterospecific neighbors were feeding than expected, and more heterospecific neighbors of white-chinned petrels, prions, and diving petrels were black-browed albatross and groups of penguins and Antarctic fur seals Arctocephalus gazella than expected by chance. We show that associations among foraging birds are not random and are not due to species-specific differences in foraging habitat. We present methods that can be used to measure and compare the strength of intra- and interspecific association among predators at sea. Our results suggest that local enhancement is an important component of the foraging strategies of Antarctic seabirds.