Stability of acoustic individuality in the alarm calls of wild yellow ground squirrels Spermophilus fulvus and contrasting calls from trapped and free-ranging callers

Abstract

The questions of individuality and stability of cues to identity in vocal signals are of considerable importance from theoretical and conservation perspectives. While individuality in alarm calls has been reported for many sciurids, it is not well-documented that the vocal identity encoded in the alarm calls is stable between different encounters with predators. Previous studies of two obligate hibernating rodents, speckled ground squirrels Spermophilus suslicus, and yellow ground squirrels Spermophilus fulvus demonstrated that, after hibernation, most individuals could not be identified reliably by their alarm calls. Moreover, in most speckled ground squirrels, individual patterns of alarm calls changed progressively over as little as 2 weeks. However, these previous data have been obtained using the collection of alarm calls from trapped animals. Here, we examined ten free-ranging dye-marked yellow ground squirrels to determine whether their alarm calls retain the cues to individuality between two encounters of surrogate predators (humans), separated on average by 3 days. Discriminant function analysis showed that the alarm calls of individual yellow ground squirrels were very similar within a recording session, providing very high individual distinctiveness. However, in six of the ten animals, the alarm calls were unstable between recording sessions. Also, we examined ten dye-marked individuals for consistency of acoustic characteristics of their alarm calls between the encounters of humans, differing in techniques of call collection, from free-ranging vs trapped animals. We found differences only in two variables, both related to sound degradation in the environment. Data are discussed in relation to hypotheses explaining the adaptive utility of acoustic individuality in alarm calls.

All Rodents Are Not the Same: A Modern Synthesis of Cortical Organization

“…Giant gerbil vocalizations are generally 1-2 kHz but can be lower; Belding's ground squirrel calls range from 2 to 10 kHz, and the yellow ground squirrel calls maximum fundamental frequency is 5-6 kHz [Matrosova et al, 2010]. The species for which call types have been well defined are often not the same species as those for which the neocortex has been well characterized in terms of tonotopic organization.…”

“…Giant gerbils (close cousins of the Mongolian gerbil) have distinct calls for different predators such as dogs, humans, and lizards [Randall et al, 2005], and individuals within a population can recognize the sex and identity of a specific individual by the acoustic properties of its call. Finally, studies of Bel ding's ground squirrel and yellow ground squirrel vocalizations indicate that they have different calls for different predators and that individuals have signature calls that distinguish them from other squirrels within their social group [Mateo, 1996;McCowan and Hooper, 2002;Matrosova et al, 2010].…”

Gender identification using acoustic analysis in birds without external sexual dimorphism

“…The fundamental frequency is the acoustic variable that most often discriminates between the calls of male and female birds. Vegetation and distance do not affect the use of frequencies to discern between genders, as fundamental frequency variables are not affected by these factors (Matrosova et al 2010). Frequency modulation: Changes in fundamental frequency contour during a call.…”

“…Amplitude: The relative intensity of calls or call components, evident from degrees of blackening on respective parts of the spectrogram. All power variables can be slightly affected by distance or vegetation cover (Matrosova et al 2010). …”

Species-specific and shared features in vocal repertoires of three Eurasian ground squirrels (genus Spermophilus)

“…fulvus: Nikoĺskii 1979S. fulvus: Nikoĺskii , 1984Titov et al 2005;Matrosova et al 2007Matrosova et al , 2010a. A pilot study of non-alarm vocalizations was done only for S. suslicus (Matrosova et al 2006).…”