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Barbary ground squirrels do not have a sentinel system but instead synchronize vigilance

Abstract

Coordinated behaviors, such as hunting in lions and coordinated vigilance as antipredator behavior, are examples of benefits of group-living. Instead of asynchronous vigilance, some social species synchronize their vigilance bouts or take turns acting as sentinels. To increase our knowledge on the evolution of vigilance behavior, we studied whether vigilance is coordinated in Barbary ground squirrels, Atlantoxerus getulus. We show that vigilance was synchronized instead of taking turns. Multiple non-mutually exclusive hypotheses could explain synchronization: Barbary ground squirrels may perch because (1) neighbors are perched (copying effect), (2) perch synchrony may be an emergent property of the ecology as all squirrels may be satiated at the same time (collective behavior), or (3) the benefits are large in terms of evading ambush predators and scanning effectiveness (watch each other’s back). Particularly, in habitats where the field of view is obstructed by man-made structures and multiple individuals may be necessary to watch for terrestrial predators, synchronized vigilance may have greater fitness benefits than sentinel behavior. We conclude that it is essential to test assumptions of coordination and, thus, to analyze coordination to describe sentinel systems.

Significance statement

Vigilance behavior can be vital to an animal’s survival. Taking turns acting as sentinels or synchronizing vigilance bouts reduces the cost of the trade-off between feeding and predation risk. A sentinel system assumes that sentinels are vigilant from raised positions, warn group members of danger, and alternate vigilance bouts. However, the assumption of alternating vigilance bouts remains poorly tested. We tested this assumption in invasive Barbary ground squirrels. We found that instead of alternating, individuals synchronized their vigilance bouts. Perch synchrony may be (1) a response to perching group members (copying effect), (2) an emergent property of the species’ ecology, and (3) an adaptation to anthropogenically altered habitats (watch each other’s back).

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Data availability

The datasets analyzed and code used during the current study are available from a GitHub repository (https://github.com/annemarievdmarel/coordinated-vigilance, van der Marel et al. 2021b).

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Acknowledgements

We acknowledge the landowners of our study sites, the IPNA-CSIC by providing a research vehicle, and the Cabildo of Fuerteventura for the use of the facilities and the help of its staff at the Estación Biológica de La Oliva. We thank the editors and 2 anonymous reviewers for their constructive feedback.

Funding

This work was supported by a University of Manitoba Faculty of Science graduate studentship, a Faculty of Graduate Studies Graduate Enhancement of the Tri-Council Stipend (GETS), the Cabildo Insular de Tenerife under the identification mark “Tenerife 2030” (P. INNOVA 2016–2021), the Natural Sciences and Engineering Research Council of Canada (grant number 04362 to JMW), the Canadian Foundation for Innovation, and the University of Manitoba University Research Grant Program.

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All authors conceived the ideas and designed methodology; AM collected the data, analyzed the data, and led the writing of the manuscript; all authors contributed critically to the drafts and gave final approval for publication.

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Correspondence to Annemarie van der Marel.

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All applicable international, national, and institutional guidelines for the care and use of animals were followed. All procedures performed were in accordance with the ethical standards of the institution or practice at which the studies were conducted (University of Manitoba Animal Care and Use Committee, protocol no. F14-032, and the government of Fuerteventura, Cabildo Insular de Fuerteventura no. 14885).

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The authors declare no competing interests.

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van der Marel, A., Waterman, J.M. & López-Darias, M. Barbary ground squirrels do not have a sentinel system but instead synchronize vigilance. Behav Ecol Sociobiol 75, 153 (2021). https://doi.org/10.1007/s00265-021-03094-1

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Keywords

  • Anti-predator behavior
  • Collective behavior
  • Coordinated vigilance
  • Invasive species
  • Mammals