Acoustic analysis of alarm calls of the European ground squirrel (Spermophilus citellus) and the Taurus ground squirrel (S. taurensis) (Mammalia: Sciuridae)

Individual-based acoustic variation of the alarm calls in the long-tailed ground squirrel

Based on their phylogenetic position, Nearctic ground squirrels are closest relatives to the long-tailed ground squirrel Urocitellus undulates even though it has Palaearctic distribution. We aimed to investigate the variability of alarm calls of the long-tailed ground squirrel to test the individual variation in alarm calls. This species is known to produce two types of alarm calls: whistle alarms and wideband calls. Although ground squirrels are a model group for the study of vocal individuality, this phenomenon has not yet been studied in a species producing two such completely different types of alarms. Most of ground squirrel species produce either whistle or wideband alarms and this species represents a unique model for testing the degree of individual variability depending on completely different acoustic structures. We analysed 269 whistle alarms produced by 13 individuals and 591 wideband alarms from 25 individuals at the western part of Lake Baikal. A discriminant function analysis (DFA) assigned 93.5% (88.9%, cross-validated result) of whistle alarms to the correct individual and 91.4% (84%) of wideband alarms. This is the first evidence of individual variation in wideband alarms compared with whistle alarms and occurrence of vocal individuality in two warning signals of a completely different acoustic structure produced by a ground squirrel.

Geographic variability in the alarm calls of the European ground squirrel

Geographic variability in vocalizations has been documented in many mammalian species. We examined to what extent it applies to the alarm calls of the European ground squirrel Spermophilus citellus. We recorded the calls of 82 adult individuals from 5 natural colonies in the Czech Republic and 24 adult individuals from an artificial seminatural colony located in a Czech zoo. The founders of this colony originated from 4 different natural colonies in the Czech Republic. Our results showed that there are hardly any differences in the acoustic structure of the alarm calls between male and female European ground squirrels. Discriminant function analysis showed the highest degree of discriminability for the most isolated sites (54-74% of individuals classified correctly), whereas the lowest degree of discriminability was found for 2 interconnected colonies (38-40% individuals classified correctly). Individuals from the artificial seminatural colony were often classified correctly to this colony (58% classified correctly); however, the precision of the classification was comparatively relatively low, that is, many individuals from other colonies were incorrectly classified into this seminatural colony. This likely corresponds to the different origins of its founders. These findings indicate that there is a rather substantial geographic variability in the alarm calls of the European ground squirrel, and our study highlights its possible impact on conservation measures such as establishing artificial colonies or reintroductions.

Phylogenetic relationship and variation of alarm call traits of populations of red-cheeked ground squirrels (Spermophilus erythrogenys sensu lato) suggest taxonomic delineation

Distribution area and taxonomic borders within the species complex Spermophilus erythrogenys sensu lato remain questionable. Early evidence suggests that red-cheeked ground squirrels of Southeast Kazakhstan are remarkably different in terms of the acoustic structure of their alarm calls from the red-cheeked ground squirrels of the Kurgan region in Russia. In this study, we analyzed the differences in the acoustic structure of the alarm call and mitochondrial DNA (complete control region, 1005-1006 bp and complete cytochrome b gene, 1140 bp) in 3 populations of red-cheeked ground squirrels (Tara, Altyn-Emel and Balkhash), all located within areas isolated by geographical barriers in Southeast Kazakhstan. We found that the alarm call variables were similar between the 3 study populations and differed by the maximum fundamental frequency (8.46 ± 0.75 kHz) from the values (5.62 ± 0.06 kHz) reported for the red-cheeked ground squirrels from the Kurgan region of Russia. Variation in mtDNA control region was only 3% and variation in cytochrome b gene was only 2.5%. Phylogenetic trees based on cytochrome b gene polymorphism of 44 individuals from the study area and adjacent territories indicated 3 clades with high (98-100%) bootstrap support: "intermedius," "brevicauda" and "iliensis"). We conclude that the 3 study populations in Southeast Kazakhstan belong to the clade intermedius and suggest a taxonomical revision of the species complex Spermophilus erythrogenys sensu lato, including analyses of nuclear DNA and alarm calls for populations of the brevicauda and iliensis clades.

Differences in alarm calls of juvenile and adult European ground squirrels (Spermophilus citellus): Findings on permanently marked animals from a semi-natural enclosure

The European ground squirrel (Spermophilus citellus) emits alarm calls that warn conspecifics of potential danger. Although it has been observed that inexperienced juveniles of this species emit alarm calls that sound similar to those of adults, studies focusing on juvenile alarm calls are lacking. We analyzed the acoustic structure of alarm calls emitted by six permanently marked European ground squirrels living in a semi-natural enclosure when they were juveniles and after 1 year as adults. We found that the acoustic structure of the juvenile alarm calls was significantly different from those of adults and that the alarm calls underwent nearly the same changes in all studied individuals. All juveniles emitted alarm calls consisting of one element with almost constant frequency, but their alarm calls included a second frequency-modulated element after their first hibernation as adults. Our data show that the duration of the first element is significantly shorter in adults than in juveniles. Additionally, the frequency of the first element is significantly higher in adults than in juveniles. Similar to previous findings in other Palearctic ground squirrel species, our data are inconsistent with the assumption that juvenile mammals emit vocalizations with higher fundamental frequencies than adults. However, our results do not support the previously suggested hypothesis that juvenile ground squirrels conceal information regarding their age in their alarm calls because we found significant differences in alarm calls of juveniles and adults.

Acoustic analysis of the alarm call of the Anatolian ground squirrel Spermophilus xanthoprymnus: a description and comparison with alarm calls of the Taurus S. taurensis and European S. citellus ground squirrels

The Anatolian ground squirrel Spermophilus xanthoprymnus like other ground-dwelling sciurids, emits alarm calls in the presence of predators. In this study, we provide a description of the acoustic structure of alarm call of this species and compare it to those of two closely related species, the Taurus ground squirrel Spermophilus taurensis and the European ground squirrel Spermophilus citellus. The alarm call of S. xanthoprymnus is a tonal sound mostly consisting of two different elements-the first element has low frequency modulation while the second element is highly frequency modulated. A similar basic structure can be found in the alarm calls of some other old world ground squirrel species of the genus Spermophilus, including S. taurensis and S. citellus. Despite this similarity, we found that these three species can be clearly distinguished on the basis of their alarm calls. Differences in the acoustic structure of S. xanthoprymnus and S. taurensis calls are especially remarkable, as these two species were considered to be conspecific until 2007. S. xanthoprymnus and S. taurensis were also demonstrated to have closer acoustic similarity, which is in contrast to results based on molecular data indicating that S. taurensis is most closely related to S. citellus.