Elsevier

Animal Behaviour

Volume 80, Issue 3, September 2010, Pages 351-361
Animal Behaviour

Articles
Call directionality and its behavioural significance in male northern elephant seals, Mirounga angustirostris

https://doi.org/10.1016/j.anbehav.2010.06.013Get rights and content

Animals often produce sounds that are focused in a particular direction relative to the caller’s orientation. Although many studies have suggested ways in which directional signal design might have behavioural significance among vocally interacting individuals, there are few direct tests using experimental approaches. During the breeding season and while fasting on land, male northern elephant seals produce airborne threat calls during dyadic interactions when competing for mating opportunities. In this study, we investigated the directional cues of these calls and tested hypotheses regarding directional signalling with respect to the behaviour of receivers during vocally mediated male agonistic interactions. We then determined effects of vocal directionality on receiver responses using an acoustic playback approach. We found that male calls had substantial directionality, particularly at higher frequencies (>1000 Hz). Subordinate males responded more strongly by retreating when the caller faced the receiver compared to when the caller was at a right angle or faced away. We also found a significant difference in responses to playback sequences with different call directivity patterns. Males displayed significantly more negative phonotaxis (i.e. moved away) in response to playbacks that simulated a caller oriented towards them compared to when playbacks simulated a caller oriented away from them. These results suggest that the directionality of threat calls provides important information about the auditory scene and spatial orientation of conspecifics and that this trait, along with the receiver’s ability to extract this information, may have evolved as a consequence of its effect on the breeding success and fitness of the individual.

Section snippets

Study Location and Animals

We made recordings and conducted behavioural observations and playbacks on a northern elephant seal rookery at Año Nuevo State Reserve located in San Mateo County approximately 35 km north of Santa Cruz, California, U.S.A. All data were collected during the breeding months of December through March over 4 years (2002–2003, 2003–2004, 2004–2005 and 2005–2006) on the mainland of the reserve. For studies 1 and 2, recordings and observational efforts were focused on one of the larger groups, which

Study 1: directivity patterns of male threat calls

In the first study, we sought to identify potentially salient directional features of male northern elephant seal threat calls by addressing the following research questions. (1) How directional are threat calls, and which frequency bands provide the most directional features? (2) Which caller orientations provide directional features that are likely to be discriminable from those of other orientations? We used clap threat calls of male northern elephant seals (Bartholomew & Collias 1962) for

Study 2: behavioural observations of male–male interactions

Given the directionality of male threat calls demonstrated in study 1, our aim in study 2 was to determine whether differences in receiver responses to threat calls depend on the caller’s orientation. We hypothesized that receivers would respond more strongly to calls projected at them compared to when calls were projected at a right angle to (90°) or away from (180°) them. Bartholomew & Collias (1962) reported that dominant males ignore the threat calls of subordinates, whereas the most

Study 3: playbacks

Although our behavioural observations supported the hypothesis that subordinate males respond more strongly to calls projected towards them, the threat display includes acoustic as well as visual cues (e.g. stereotyped posturing during calling, as described above). Thus, we used a playback approach to isolate the acoustic component of this multimodal signal. Vocal directionality results in both overall sound pressure level and frequency component differences, so we allowed both to covary in our

General discussion

During the breeding season, male northern elephant seals defend groups of females in oestrus. This system of female defence polygyny is mediated by threat-escalating behaviour that serves to delineate and maintain hierarchical status between sexually competing males. In study 1, directivity patterns and the directivity index of threat calls by four adult males and two older subadult males were determined based on five orientation categories. We found that the broadband, overall measurement of

Acknowledgments

We thank several individuals for their assistance in the field including Michelle Hanenburg, Kristy Lindemann, Colleen Reichmuth, Asila Ghoul, Logan Medina, and especially Elizabeth Atwood, who conducted all caller–receiver distance measurements. Logistical support for research conducted at Año Nuevo State Reserve was provided by Dr Daniel Costa, Dr Daniel Crocker, Dr Dave Casper, Patricia Morris, Sue Reynoldson and Gary Strachan and the other park rangers at Año Nuevo. Funding from the Office

References (37)

  • T.U. Grafe et al.

    Frogs flee from the sound of fire

    Proceedings of the Royal Society B

    (2002)
  • M.M. Holt et al.

    Spatial release from masking of aerial tones by pinnipeds

    Journal of the Acoustical Society of America

    (2007)
  • M.M. Holt et al.

    Localization of aerial broadband noise by pinnipeds

    Journal of the Acoustical Society of America

    (2004)
  • M.M. Holt et al.

    Localization of aerial pure tones by pinnipeds

    Journal of the Acoustical Society of America

    (2005)
  • S.L. Hopp et al.

    Sound playback studies

  • M.L. Hunter et al.

    Directionality of avian vocalizations: a laboratory study

    Condor

    (1986)
  • S.J. Insley et al.

    Source levels of northern elephant seal vocalization in air

    Journal of the Acoustical Society of America

    (2005)
  • D. Kastak et al.

    In-air and underwater hearing sensitivity of a northern elephant seal (Mirounga angustirostris)

    Canadian Journal of Zoology

    (1999)

    • Cited by (0)

    1

    B. L. Southall is now at Southall Environmental Associates, 911 Center Street, Suite B, Santa Cruz, CA 95060, U.S.A.

    2

    S. J. Insley is now at the Department of Biology, University of Victoria, P.O. Box 3020, Station CSC, Victoria, BC V8W 3N5, Canada.

    View full text
    Copyright © 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.