Frequency-modulated second elements of two-element alarm calls do not enhance discrimination of callers in three Eurasian ground squirrels
Abstract
Alarm calls of the European Spermophilus citellus (EGS), Taurus S. taurensis (TGS) and Anatolian S. xanthoprymnus (AGS) ground squirrels share the same basic structure. They are tonal sounds consisting primarily of two different elements.
The first element, often produced without the second element, has limited frequency modulation, while the second element is more frequency modulated. The present study examined whether this frequency-modulated element enhances the individual distinctiveness of calls, allowing calls to be ascribed with greater confidence to individual callers of the three species.
Cross-validated discriminant function analysis (DFA) based on five acoustic parameters of the first element successfully classified calls to correct individuals (EGS: 90%, TGS: 98%, AGS: 96%). Cross-validated DFA based on five acoustic parameters of the second element was also successful in classifications (EGS: 88%, TGS: 86%, AGS: 96%), though discrimination of callers based on parameters of the second versus first element was the same for the AGS, lower for the EGS and significantly lower for the TGS.
Cross-validated DFA based on five acoustic parameters of two-element calls also successfully classified calls to correct individuals (EGS: 93%, TGS: 98%, AGS: 97%), though did not improve the extent to which calls could be classified to individuals beyond that based on the first element alone. Thus, the second element does not enhance the individual distinctiveness of calls, but may convey other information such as the location of the caller [Current Zoology 58 (5): 749-757, 2012].