Use of Social Information in Seabirds: Compass Rafts Indicate the Heading of Food Patches

Henri Weimerskirch,Elisa Goya,Jaime Silva,Jose Carlos Marques,Sophie Bertrand,Brian Gratwicke

doi:10.1371/journal.pone.0009928

Abstract

Ward and Zahavi suggested in 1973 that colonies could serve as information centres, through a transfer of information on the location of food resources between unrelated individuals (Information Centre Hypothesis). Using GPS tracking and observations on group movements, we studied the search strategy and information transfer in two of the most colonial seabirds, Guanay cormorants (Phalacrocorax bougainvillii) and Peruvian boobies (Sula variegata). Both species breed together and feed on the same prey. They do return to the same feeding zone from one trip to the next indicating high unpredictability in the location of food resources. We found that the Guanay cormorants use social information to select their bearing when departing the colony. They form a raft at the sea surface whose position is continuously adjusted to the bearing of the largest returning columns of cormorants. As such, the raft serves as a compass signal that gives an indication on the location of the food patches. Conversely, Peruvian boobies rely mainly on personal information based on memory to take heading at departure. They search for food patches solitarily or in small groups through network foraging by detecting the white plumage of congeners visible at long distance. Our results show that information transfer does occur and we propose a new mechanism of information transfer based on the use of rafts off colonies. The use of rafts for information transfer may be common in central place foraging colonial seabirds that exploit short lasting and/or unpredictably distributed food patches. Over the past decades Guanay cormorants have declined ten times whereas Peruvian boobies have remained relatively stable. We suggest that the decline of the cormorants could be related to reduced social information opportunities and that social behaviour and search strategies have the potential to play an important role in the population dynamics of colonial animals.

Highlights

Animals living or gathering in groups at certain period of their life can use personal information obtained from environmental cues and social information from the behaviour of congeners to make decisions [1,2]
Because sea birds rely on food resources that are patchily distributed, with location being highly variable in space and time [6,9], breeding in colonies could provide the opportunity for individuals to obtain information about the location of favourable food patches by watching the behaviour of other individuals when returning from, or leaving for feeding grounds
The first, and most important, result of this study indicates clearly that Information Transfer does occur in a colonial seabird through a specific signalling behaviour, by forming a compass raft

Summary

Introduction

Animals living or gathering in groups at certain period of their life can use personal information obtained from environmental cues and social information from the behaviour of congeners to make decisions [1,2]. Because sea birds rely on food resources that are patchily distributed, with location being highly variable in space and time [6,9], breeding in colonies could provide the opportunity for individuals to obtain information about the location of favourable food patches by watching the behaviour of other individuals when returning from, or leaving for feeding grounds. Most empirical studies have focused on the demonstration that individuals follow from the colony successful foragers heading to feeding grounds, whereas information exchange may occur outside the colony and be based on the observation of the returning successful individuals [11,12]

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