In addition to encoding referential information and information about the sender’s motivation, mammalian alarm calls may encode information about other attributes of the sender, providing the potential for recognition among kin, mates, and neighbors. Here, we examined 96 speckled ground squirrels (Spermophilus suslicus), 100 yellow ground squirrels (Spermophilus fulvus) and 85 yellow-bellied marmots (Marmota flaviventris) to determine whether their alarm calls differed between species in their ability to encode information about the caller’s sex, age, and identity. Alarm calls were elicited by approaching individually identified animals in live-traps. We assume this experimental design modeled a naturally occurring predatory event, when receivers should acquire information about attributes of a caller from a single bout of alarm calls. In each species, variation that allows identification of the caller’s identity was greater than variation allowing identification of age or sex. We discuss these results in relation to each species’ biology and sociality.

Apart from the alerting function of alarm calls, selection may favor cues that help individuals to distinguish between reliable and unreliable caller

Zoo and wildlife management faces a problem with bird sexing, as many bird taxa have indiscernible gender differences in size and coloration. Problematic groups are geese, cranes, rails, raptors, owls, parrots, doves, auks, shearwaters and some passerines. Commonly accepted invasive sexing techniques based on genetics, laparoscopy, morphometric and on cloacal inspection, are all needed in bird capturing and handling. Capturing and subsequent manipulations may be inapplicable for free-ranging birds, whereas distant voice-based sexing is relevant for many species. This review evaluates the potential for noninvasive sexing by separate calls or duet calls, for adult birds of 69 species from 16 orders and for chicks of 11 species from 7 orders. For adult birds of 25 species, a single call per individual was sufficient for 100 % reliable sexing by ear or using spectrographic analysis. For chicks, the potential for voice-based sexing seems to be very limited. For birds calling rarely or unpredictably, we propose a simple way of provoking vocalization using playbacks of species-specific calls that are available from sound libraries. We conclude that sexing by voice may represent a feasible alternative to the classical sexing techniques, both in the wild and in captivity.

In most species, acoustical cues are crucial for mother-offspring recognition. Studies of a few species of ungulates showed that potential for individual recognition may differ between nasal and oral contact calls. Vocalizations of 28 hinds and 31 calves of farmed Iberian red deer (Cervus elaphus hispanicus) were examined with discriminant function analyses (DFA) to determine whether acoustic structure of their oral and nasal contact calls encodes information about the caller’s identity. Contact calls were elicited by brief separation of individually identified animals by a distance over 10 m or by a bar fence. Both oral and nasal calls of both hinds and calves showed high potential to discriminate individuals. In hinds, individuality was significantly higher in the oral than in the nasal calls, whereas in calves, individuality was equally well expressed in both oral and nasal calls. For calves, the maximum fundamental frequency was higher and the duration was longer in oral calls than in nasal calls. For hinds, the maximum fundamental frequency and the duration were indistinguishable between oral and nasal calls. Compared to the pooled sample of oral and nasal calls, separate oral or nasal call samples provided better classifying accuracy to individual in either hinds or calves. Nevertheless, in both hinds and calves, even in the pooled sample of oral and nasal calls, the degree of individual identity was 2–3 times greater than expected by chance. For hinds that provided calls in both years, cross-validation of calls collected in 2012 with discriminant functions created with calls from 2011 showed a strong decrease of classifying accuracy to individual. These results suggest different potentials of nasal and oral calls to allow the discrimination of individuals among hinds, but not among red deer calves. The high potential of individual recognition even with the pooled sample of oral and nasal calls allows mother and young to remember only one set of acoustic variables for mutual vocal recognition. Poor between-year stability of individual characteristics of hind oral and nasal calls would require updating keys to individual recognition each calving season.