Elsevier

Animal Behaviour

Volume 73, Issue 5, May 2007, Pages 747-762
Animal Behaviour

Vocalizations of male bearded seals, Erignathus barbatus: classification and geographical variation

https://doi.org/10.1016/j.anbehav.2006.06.012Get rights and content

Comparative studies of vocal repertoires over the geographical range of a species can improve our understanding of the function and evolution of animal vocalizations. They may also help to elucidate relationships between populations, where genetic studies are missing or difficult to perform. We recorded male bearded seal vocalizations from four sites throughout their Arctic distribution. We measured 16 parameters for each vocalization and examined variability using classification tree analyses. There were four major call categories: trill, ascent, sweep and moan. Trills divided further into three subcategories: trills with ascent/plume, long trills and short trills. Not all call categories were present at all sites: the ascent occurred only in Alaska and western Canada, the sweep occurred only in Svalbard and in the High Canadian Arctic, and the trill with ascent/plume occurred at all sites except Svalbard. Geographical differences between sites were apparent in repertoire size as well as in vocal structure. Furthermore, an east–west gradient in structural similarities between call types was apparent. The vocal repertoire of bearded seals seemed to be relatively stable; for example, over a period of 16 years no calls were lost or added to the Alaskan repertoire. The most likely explanation for the observed vocal differences between sites is the geographical isolation of populations by physical distance. Other factors, such as varying ecological influences (e.g. adaptation to varying ice habitats) or sexual selection, may also contribute to vocal variability and result in the observed geographical variation.

Section snippets

Sampling Procedures and Measurements

We obtained recordings of male bearded seals from four sites during the April–June mating season of this species. At each site recordings were acquired over several years between 1972 and 2001 in Alaska (1985, 1992–1993, 2000–2001), Svalbard (1999–2000), western Canadian Arctic (1972–1975) and the Canadian High Arctic (1976, 1981–1982; Fig. 1, Appendix Table A1). The Alaska and Svalbard recordings were each acquired at a single location (Point Barrow, Alaska and Kongsfjorden, Svalbard), whereas

Vocal Classification

We analysed a total of 3835 vocalizations for Alaska (N = 2319), Svalbard (N = 833), the Canadian High Arctic (N = 530) and the western Canadian Arctic (N = 153). We initially divided vocalizations into four basic call categories by visual inspection of the sound spectrogram: trill (T), moan (M), sweep (S) and ascent (A). The names of these categories are consistent with those used in earlier studies on bearded seal vocalizations (Cleator et al., 1989, Budelsky, 1992, Van Parijs et al., 2001). For each

Discussion

The comparison of bearded seal vocal repertoires throughout the four Arctic study sites revealed macrogeographical variation on the level of shared call categories and in vocal structure. Repertoires differed in readily discernible ways, either through the presence of certain call categories (e.g. the sweep vocalization was present only in Svalbard and the Canadian High Arctic; Fig. 3) or through structural differences in shared call types. Van Parijs et al., 2003a, Van Parijs et al., 2004

Acknowledgments

We thank the numerous people who, over the years, helped with recording in the field, especially G. N. Ahmaogak, Sr, T. Albert, T. Hepa and C. D. N. Brower of the North Slope Borough Department of Wildlife Management for their steadfast support (Alaska); B. Krafft (Svalbard); H. Cleator, W. Calvert and D. Andriashek (Canadian Arctic). We are grateful to D. Ponirakis, M. Fowler and S. Smith for their help with digitizing the Alaskan and Canadian recordings. We thank the Alaska Eskimo Whaling

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      While all ice-breeding seals are known to produce underwater vocalizations (e.g., Stirling and Siniff, 1979; Watkins and Ray, 1985; Perry and Terhune, 1999; Jones et al., 2014; Cziko et al., 2020), bearded seals, given their highly vocal nature, are good candidates for passive acoustic monitoring, particularly during the breeding season. Only males are thought to call underwater during the breeding season (Ray et al., 1969; Cleator et al., 1989; Davies et al., 2006), and have shown geographical variation in repertoires that may be indicative of discrete breeding stocks (Cleator et al., 1989; Risch et al., 2007; Charrier et al., 2013). In the U.S. Arctic, male bearded seals produce primarily three call types, trills, ascents, and moans, which appear to be stable over long temporal scales (Risch et al., 2007; Jones et al., 2014; Frouin-Mouy et al., 2016).

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    1

    C. W. Clark and P. J. Corkeron are at the Bioacoustics Research Program, Cornell Laboratory of Ornithology, 159 Sapsucker Woods Road, Ithaca, NY 14850-1999, U.S.A.

    2

    A. Elepfandt is at the Institut für Biologie, Humboldt-Universität Berlin, Invalidenstr. 43, 10115 Berlin, Germany.

    3

    K. M. Kovacs and C. Lydersen are at the Norwegian Polar Institute, N-9296 Tromsø, Norway.

    4

    I. Stirling is at the Canadian Wildlife Service, 5320 122 Street, Edmonton, AB T6H 3S5, Canada.

    5

    S. M. Van Parijs is at the Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543-1026, U.S.A.

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