Population density does not affect the alarm call characteristics in the Speckled Ground Squirrel (Spermophilus suslicus) [Populační hustota neovlivňuje vlastnosti varovných signálů sysla perličkového (Spermophilus suslicus)]

Pages 333–342
Lynx, new series | 2008/39/2

While the environmental effects on animal vocalizations have been studied in many birds, mammals and in particular in the ground-dwelling sciurids, the influence of social surrounding on the call structure is poorly understood. The main idea we test here is that in the animals using alarm calls to warn kin of potential predators, vocal characteristics could be adjusted according to the changes in interindividual distances between conspecifics. At higher population density, the distance between individuals becomes shorter. The increasing frequency of the alarm calls will make them less perceptible to predators, as they will propagate at shorter range compared to the lower-frequency ones. In this study, we compare alarm call characteristics of 28 speckled ground squirrels repeatedly tested in years with low and high population density. Whereas population density decreased three times in the three subsequent study years, fundamental frequency of the alarm calls did not decrease in response to the increase of the interindividual distance. Our findings suggest that speckled ground squirrels do not adjust characteristics of their alarm calls to the shortening distance between conspecifics.

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