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Marine Ecology Progress Series

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MEPS 336:267-274 (2007)  -  doi:10.3354/meps336267

Female–female aggression: structure of interaction and outcome in loggerhead sea turtles

Gail Schofield1,2,*, Kostas A. Katselidis1,3, John D. Pantis4, Panayotis Dimopoulos1, Graeme C. Hays2

1Department of Environmental & Natural Resources Management, University of Ioannina, G. Seferi 2, 30100 Agrinio, Greece
2Department of Biological Sciences, Institute of Environmental Sustainability, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK
3National Marine Park of Zakynthos, 1 El. Venizelou Street, 29100 Zakynthos, Greece
4Department of Ecology, School of Biology, UP Box 119, Aristotle University of Thessaloniki, 54006 Thessaloniki, Greece

ABSTRACT: Aggressive behaviour between females of the same species is not widely documented, particularly in marine vertebrates. During a 3 yr in-water survey at the temperate loggerhead sea turtle Caretta caretta breeding area of Zakynthos, Greece, female–female interactions comprised 4% of all female loggerhead sighting events (n = 60 out of 1449 events). Male–female interactions comprised an additional 4% of sighting events, while 92% were of solitary females. The structure of interactions was analysed for 58 of these sighting events, each lasting an average of 3.4 min (SD ± 1) and comprising a total of 3.1 h observation time. We found that interactions involved ritualized escalation in behaviour from passive threat displays (e.g. head–tail circling) to aggressive combat (e.g. sparring). We suggest that circling individuals evaluate opponent size, sparring individuals test opponent strength, and that the positioning of the prehensile tail signals motivational intent to either escalate or abort. The presence of intruder females triggered a passive response in 100% of events involving basking and swimming turtles (n = 19); although residents resting on the seabed only responded on 69% of occasions (n = 27), their response was almost 4 times more likely to escalate to one of aggression. Our results suggest that certain sites may be preferentially sought after and defended by sea turtles.

KEY WORDS: Caretta caretta · Sequential assessment · Evolutionary stable strategy · Territory · Marine · Vertebrate · Reptile

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