Elsevier

Animal Behaviour

Volume 93, July 2014, Pages 249-260
Animal Behaviour

All signals are not equal: acoustic signalling of individuality, sex and breeding status in a cooperative breeder

https://doi.org/10.1016/j.anbehav.2014.05.007Get rights and content

Highlights

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    We examined call variability in six different call types.

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    Not all calls reflected the same extent of information.

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    Call variation was affected by individual identity in three call types.

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    Call variation was affected by breeding status in two call types.

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    Some, but not all, acoustic signals may be selected for individual distinctiveness.

Repeated interactions between individuals in socially living animals select for the evolution of signals that convey information identifying individuals or categories of individuals, which may enable the discrimination of familiar versus unfamiliar individuals. Such information may help animals maximize their inclusive fitness by adjusting their own behaviour, allowing them to avoid conflict, preferentially direct help and/or ignore unreliable individuals. Acoustic signals in birds provide the potential to encode individual-specific information. We examined the degree to which individual identity, sex, breeding status, group membership and genetic relatedness were related to variability in six different call types, which occurred across a variety of different behavioural contexts in the apostlebird, Struthidea cinerea, a socially living and cooperatively breeding Australian passerine. We demonstrated that not all calls reflected the same extent of information. Of the six call types, call variation was related to individual identity in three call types, breeding status in two call types and sex and group relatedness in one call type. Finally, variation in two call types was not related to any of the measured variables. Our results suggest that some, but not all, acoustic signals in apostlebirds may be selected for individual distinctiveness between individuals and categories of individuals (male versus female, breeder versus nonbreeder), and these signals may be important in determining levels of cooperation and interaction between individuals in this cooperatively breeding society.

Section snippets

Study Population and Vocalization Recordings

We recorded vocalizations of 60 free-living adult apostlebirds (19 breeding males, 17 nonbreeding males, 13 breeding females and 11 nonbreeding females) from 15 social groups at the University of New South Wales Arid Zone Research Station at Fowlers Gap (142°E, 31°S, New South Wales, Australia). Vocalizations were recorded in the spring from August to December in both 2010 and 2011 and also during the autumn in April and May 2011.

This study population was monitored between 2004 and 2012, and

Noise has Little Effect (<1%) on SPCC

Background noise was not random: all noise clips compared against each other were correlated on average at 0.36 ± 0.001, all noise clips from the same group (same location) were slightly more correlated at 0.38 ± 0.003 and noise clips compared between different groups were correlated at 0.36 ± 0.001. However, background noise accounted for less than 1% of the variation in SPCC values. The average SPCC was 0.248 ± 0.001 for unfiltered calls and 0.238 ± 0.001 for filtered calls using Raven Pro 1.4, and

Discussion

Our results suggest that some, but not all, acoustic signals in apostlebirds may be selected for individual distinctiveness or kin or breeding status signatures. We demonstrated that variability in call types was not equally affected by individual identity, kinship, group membership, sex or breeding status. Of the six call types, variability in three call types (‘contact call’, ‘social call’ and the piping call) was affected by individual identity. Variability in two additional call types (nest

Acknowledgments

During the entire Apostlebird project, 2004–2011, many have helped with fieldwork and banding birds, including Nichola Rahaini and Andy Russell. Thanks also go to Benjamin Warrington for computer programming and software assistance. Aliza Sager assisted with collection of acoustic data in 2011. M.W. was supported by a Macquarie University Research Excellence Scholarship, P.M. by a Macquarie University Fellowship and S.G. by an ARC QEII Fellowship.

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    Miyako H. Warrington is now at Natural Resources Institute, University of Manitoba, 70 Dysart Rd., Winnipeg, MB R3T 2N2, Canada.

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