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

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 Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 336: [267][268][269][270][271][272][273][274] 2007 plays of physical attributes (Ruby 1978), and only escalate into costly aggressive (agonistic) interaction if neither competitor retreats (Enquist & Leimar 1983). The outcome of escalated contests depends on a range of parameters such as competitive ability (resource holding power) and occupancy of a territory or hierarchical rank (prior residency effect). The residing individual is usually expected to win because, over time, the optimal sites/ranks are occupied by superior competitors (evolutionary stable strategies; Maynard Smith & Price 1973, Parker 1974. However, a range of factors associated with individual fitness and/or resource value may also affect competitor motivation and hence contest outcome (pay-off asymmetries such as contest duration and previous encounters; Kotiaho et al. 1999, Cressman et al. 2004.Although aggressive behaviour and contest escalation is widely documented for many vertebrates and invertebrates, direct observations of the aggressive behaviour of free-living animals in the marine environment is primarily limited to captive studies, usually of fish (Bisazza & Pilastro 1997). Most research on large free-living marine animals relies on the attachment of electronic devices, such as data-loggers and satellite transmitters, to elucidate animal behaviour (e.g. of fish, seabirds, seals, whales, dolphins and sea turtles) related to div...

Habitat selection by green turtles in a spatially heterogeneous benthic landscape in Dry Tortugas National Park, Florida

“…We did not detect any FF combinations even though it was possible. This result is potentially because of femalefemale aggression as reported for loggerheads (Schofield et al 2007); however, the temporal analysis did not show step-time differences by gender combination, in part due to the large variability and the small number of combinations detected in the same day.…”

“…birds by Ward & Schlossberg 2004; reptiles by Stamps 1991), while a comparably small number of studies exist in the marine realm (e.g. turtles by Schofield et al 2006Schofield et al , 2007; fish by Lecchini et al 2007). This is likely due to the challenges involved in observing individuals during experiments.…”

“…Lanyon et al (1989) described that green turtles do not form organized groups; during courtship they use visual and chemical cues to find each other (Ernst et al 1994, Spotila 2004. Bjorndal (1980) reported an absence of aggressive behavior and an indication of a hierarchy for some green turtle populations, whereas Schofield et al (2007) observed aggressive behavior between female loggerheads Caretta caretta during courtship and inter-nesting periods. During foraging periods, habitat selection is influenced by environmental factors such as resource availability and water depth (Seminoff et al 2002, Senko et al 2010), but little is known about the effect of conspecific proximity.…”

Bahamas connection: residence areas selected by breeding female loggerheads tagged in Dry Tortugas National Park, USA

“…Female-female aggression including threat displays, biting, and chasing, has been documented in Mediterranean loggerheads during breeding periods [68], but observations of loggerheads interacting at Bahamian residence areas are lacking. Determining available food resources and rest sites through benthic characterization as well as ascertaining fine-scale loggerhead behavior at these residence areas would therefore be useful for understanding how distribution of turtles may match that of 'optimal' resources and for verifying not only foraging behavior but also existence of potential loggerhead territories.…”

Individual Recognition

“…Hays et al, 2001;James et al, 2005) as males very rarely emerge onto land (but see Rice & Balazs, 2008). Photo identification will allow a new era of experimental and ecological studies of male turtles, allowing, for example, the behaviours of known individuals to be assessed (Schofield et al, 2006;Schofield et al, 2007b). In addition, photoidentification will allow the interval between successive breeding seasons (the remigration interval) to be established.…”