Ground Squirrels Have Voices that Are Similar to Those of Their Relatives

Stacie Hooper – slhooper@ucdavis.edu
Brenda McCowan – bjmccowan@ucdavis.edu
University of California, Davis
One Shields Avenue
Davis, CA 95616

Toni Lyn Morelli – morelli@berkeley.edu
Christina Kastely – yokastely@berkeley.edu
University of California, Berkeley
110 Sproul Hall
Berkely, CA 94720-5800

Popular version of paper 4pABb2, presented at the th 164th ASA Meeting, Kansas City, Missouri.

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Animal vocalizations contain information, such as the location and quality of a food source, the presence of predators, or even the identity of the caller (Blumstein and Munos, 2005; Bradbury and Vehrencamp, 1998). For example, male birds often sing their own distinct versions of a species’ song; this fact has been used to census and monitor songbird populations for some time (McGregor and Peake, 1998). With the exceptions of whales, dolphins, and bats however, few studies have explored the potential of using the information in vocalizations to census and monitor mammalian populations (Hartwig 2005). Even relatively simple vocalizations, such as alarm calls, can contain several different types of information about the caller, including their identity (Slobodchikoff and Placer, 2006).

To explore the feasibility of using information in the calls of terrestrial mammals to census populations, we looked for individual, age-class, and sex-related information in the alarm calls of Belding’s ground squirrels (Spermophilus beldingi). These ground squirrels live in colonies of related females and their dependent offspring, with males occupying territories on the colony’s edge (Mateo, 2003). While males do produce alarm calls, most are given by adult females in an attempt to warn their offspring of danger. Whistles are given in response to aerial predators such as hawks, single chirps are given to slow-moving terrestrial predators such as humans, or to remind others to remain vigilant, such as when a predator has recently left the area (Mateo, 2003; Owings et al., 1986) (A Belding’s ground squirrel chirp). Trills are a series of notes that are typically produced in response to more dangerous terrestrial predators such as bobcats and coyotes (Sherman, 1980) (A Belding’s ground squirrel trill).

We recorded chirps and trills from adult and juvenile Belding’s ground squirrels at multiple distinct locations in Yosemite National Park. We used a computer software program called Praat to measure several variables from each call, such as mean frequency and duration, and then used a neural network, or learning algorithm, to classify calls based on these variables. The network successfully classified alarm calls to individual, age-class and sex, demonstrating that this species’ alarm calls contain at least three different kinds of information about the caller. From these variables we also calculated an index of vocal similarity between individuals, and we noticed that some squirrel’s voices were more similar to each other than to others.

Our previous work with golden-mantled ground squirrels (Spermophilus lateralis) suggested that these vocal similarities may reflect close kin relationships (Hooper, 2010). To investigate whether this was true for Belding’s ground squirrels, we recorded alarm calls and collected tissue samples from adult and juvenile Belding’s ground squirrels at multiple distinct locations in the Sierra Nevada Mountains and Modoc plateau. Alarm calls were measured as before, yielding an index of vocal similarity. We extracted DNA from the tissue samples, and calculated a measure of genetic relatedness between individuals using GenePop software. Vocal similarity and genetic relatedness were compared using a Mantel test, and the results confirmed that related squirrels had more similar voices than unrelated squirrels.

Our results indicate that vocalizations such as alarm calls have the potential to provide additional information about mammalian populations to wildlife managers, including census data. It is also possible that the level of vocal similarity in a population provide information about the level of inbreeding, which could indicate whether a population is becoming genetically isolated and therefore vulnerable to the effects of inbreeding depression.

References

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Bradbury, J. and Vehrencamp, S. 1998. Principles of Animal Communication. Sinaur Associates: Massachusetts.

Hartwig, S., 2005. Individual acoustic identification as a non-invasive conservation tool: an approach to the conservation of the African wild dog Lycaon pictus (Temminck, 1820). Bioacoustics 15, 35-50.

Hooper, S. L. 2010. Impacts and applications: Developing a bioacoustic tool for mammals and measuring the effects of highway noise on a mammalian communication system, using ground squirrels as a model. Ph.D. thesis. University of California, Davis, Davis, CA.

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McGregor, P. K. and Peake, T. M., 1998. The role of individual identification in conservation biology. In: Caro, T. M. (Ed.), Behavioral Ecology and Conservation Biology, Oxford University Press, New York. pp. 31-55.

Owings, D. H., Hennessy, D. F., Leger, D. W., and Gladney, A. B. 1986. Different functions of “alarm” calling for different time scales: a preliminary report. Behavior 99, 101-116.

Sherman, P. W. 1980. The limits of ground squirrel nepotism. In: Barlow, G.W. and Silverberg, J. (Eds.), Sociobiology: Beyond Nature/nurture? Westview Press, Boulder, Colorado, pp. 505-544.

Slobodchikoff, C. and Placer, J. 2006. Acoustic structures in the alarm calls of Gunnison’s prairie dogs. The Journal of the Acoustical Society of America 119, 3153-3160.