A biologging perspective to the drivers that shape gregariousness in dusky dolphins
Knowledge of proximate (causation and development) and ultimate (evolution and survival function) causes of gregariousness is necessary to advance our knowledge of animal societies. Delphinids are among the most social taxa; however, fine-scale understanding of their intra-specific relationships is hindered by the need for underwater observations on individuals. We developed a non-invasive animal-borne camera system with the goal of examining influences on gregariousness in dusky dolphins (Lagenorhynchus obscurus). We analyzed video and diving records from 11 individual dusky dolphins off Kaikoura, New Zealand. We examined the influence of biologger attachment on dolphin behavior and tested hypotheses regarding the effects of physiology, predation, and inter-individual variation on conspecific interactions. Dolphins did not exhibit increased rates of descent or ascent in the minutes immediately following biologger attachment, indicating a lack of behavioral response. Respiration rate was positively related to dive depth and duration, suggesting that diving is energetically expensive for this species. Gregariousness was negatively related to dive depth providing evidence that the physiological constraints of diving are likely to limit social behavior. Calves were not observed more frequently in infant (vs. echelon) position with increasing depth, highlighting the likelihood of other anti-predation strategies (e.g., dilution effect) in mother-calf pairs. We found that gregariousness differed between individuals within similar social groups, suggesting the importance of collecting data at the individual level. The evidence presented herein suggests that the further development of animal-borne camera systems will yield further insight into the mechanisms underlying delphinid social behavior.
Dolphins are highly social and thus excellent model species for examining the cause and function of gregariousness. However, their cryptic nature poses a challenge to collecting the fine-scale data at the individual level required to conduct rigorous hypothesis tests. We overcame this obstacle by deploying a non-invasive cutting-edge biologger on free-ranging dusky dolphins to collect information on diving behavior, physiology, gregariousness, and mother-calf strategies. Results indicate that diving is energetically expensive, even to relatively shallow depths, and these costs likely hinder gregariousness at depth. Individual differences in gregariousness were apparent and as expected in this fission-fusion society. Unexpectedly, mother-calf pairs appeared to utilize strategies other than spatial positioning to minimize predation risk. This study advanced knowledge of dolphin social life and helps to improve the degree of data resolution in cetaceans to a level on par with terrestrial studies.
KeywordsDusky dolphin Gregariousness Predation Maternal strategies Diving behavior Biologging
Thanks to: A. Garnier, E. Hill, A. Judkins, D. Lundquist, C. Pearson, M. Srinivasan, and J. Weir for field assistance; M. Morrissey/Department of Conservation (DOC) and B. and M. Würsig for use of their research vessels and other field support; S. Gan for assistance with video analysis; and two anonymous reviewers for their helpful critiques.
This study was funded by a National Geographic Society/Waitt Fund Grant (#W365-14); a grant from the Encounter Foundation; the Faculty of Veterinary Science and School of Electrical and Information Engineering, The University of Sydney; and the University of Alaska Southeast. This material is based in part upon work supported by the Alaska NASA EPSCoR Program (NNX13AB28A).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This study was conducted under the University of Alaska Fairbanks IACUC 490961-8, Massey University Animal Ethics Committee approval MU13/90, and DOC permit 37696-MAR. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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