title: Group foraging in Socotra cormorants: A biologging approach to the study of a complex behavior.
abstract: Group foraging contradicts classic ecological theory because intraspecific competition normally increases with aggregation. Hence, there should be evolutionary benefits to group foraging. The study of group foraging in the field remains challenging however, because of the large number of individuals involved and the remoteness of the interactions to the observer. Biologging represents a cost-effective solution to these methodological issues. By deploying GPS and temperature-depth loggers on individuals over a period of several consecutive days, we investigated intraspecific foraging interactions in the Socotra cormorantPhalacrocorax nigrogularis, a threatened colonial seabird endemic to the Arabian Peninsula. In particular, we examined how closely birds from the same colony associated with each other spatially when they were at sea at the same time and the distance between foraging dives at different periods of the day. Results show that the position of different birds overlapped substantially, all birds targeting the same general foraging grounds throughout the day, likely following the same school of fish. There were as many as 44,500 birds within the foraging flock at sea at any time (50% of the colony), and flocking density was high, with distance between birds ranging from 8 to 1,380 m. Birds adopted a diving strategy maximizing time spent underwater relative to surface time, resulting in up to 72% of birds underwater in potential contact with prey at all times while foraging. Our data suggest that the benefits of group foraging outweigh the costs of intense aggregation in this seabird. Prey detection and information transmission are facilitated in large groups. Once discovered, shoaling prey are concentrated under the effect of the multitude. Fish school cohesiveness is then disorganized by continuous attacks of diving birds to facilitate prey capture. Decreasing population size could pose a risk to the persistence of threatened seabirds where group size is important for foraging success.
authors.affiliation: Department of Evolutionary Ecology Evolutionary Ecophysiology Team Institute of Ecology and Environmental Sciences University Pierre et Marie Curie Paris France; FitzPatrick Institute of African Ornithology DST-NRF Centre of Excellence University of Cape Town Rondebosch South Africa.
authors.forename: Timothée R
authors.identifier: 0000-0003-2354-824X
authors.initials: TR
authors.lastname: Cook
authors.affiliation: Department of Biology United Arab Emirates University Al Ain United Arab Emirates.
authors.forename: Rob
authors.initials: R
authors.lastname: Gubiani
authors.affiliation: FitzPatrick Institute of African Ornithology DST-NRF Centre of Excellence University of Cape Town Rondebosch South Africa.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Ryan
authors.affiliation: Department of Biology United Arab Emirates University Al Ain United Arab Emirates.
authors.forename: Sabir B
authors.initials: SB
authors.lastname: Muzaffar
keywords: anchovy; communal; cooperative; fisheries; sardine; social