Disentangling canid howls across multiple species and subspecies: Structure in a complex communication channel

Abstract

Wolves, coyotes, and other canids are members of a diverse genus of top predators of considerable conservation and management interest. Canid howls are long-range communication signals, used both for territorial defence and group cohesion. Previous studies have shown that howls can encode individual and group identity. However, no comprehensive study has investigated the nature of variation in canid howls across the wide range of species. We analysed a database of over 2000 howls recorded from 13 different canid species and subspecies. We applied a quantitative similarity measure to compare the modulation pattern in howls from different populations, and then applied an unsupervised clustering algorithm to group the howls into natural units of distinct howl types. We found that different species and subspecies showed markedly different use of howl types, indicating that howl modulation is not arbitrary, but can be used to distinguish one population from another. We give an example of the conservation importance of these findings by comparing the howls of the critically endangered red wolves to those of sympatric coyotes Canis latrans, with whom red wolves may hybridise, potentially compromising reintroduced red wolf populations. We believe that quantitative cross-species comparisons such as these can provide important understanding of the nature and use of communication in socially cooperative species, as well as support conservation and management of wolf populations.

Characterising the vocal repertoire of the Indian wolf (Canis lupus pallipes)

“…Besides having smaller body size, the mean Fundamental Frequency of the Indian wolf howl (0.422±0.126 KHz) was similar as compared to other Holarctic clade subspecies reported by Hennelly et al [46]. Since the howl is the most detectable vocalisation used in long-range social cohesion and territorial advertisement [8,22], our high howl sample size shouldn’t be considered as the most dominant vocalisation. Barking-howl, which was mentioned by many authors as a common type of mix vocalisation in wolves [22,27,47], falls under the same cluster along with howling (Figure 7b).…”

“…Overall, our study identified four statistically classified groups of vocalisations of the Indian wolf. While the howl has been extensively studied in its behavioural function and variation across subspecies [8,46], less is known about the short-range communication among wolves. For example, our study identified the ‘Social Squeak’, or the ‘talking’ like vocalisation in the wolf, yet little is known about its function in wolf packs and if it’s a common communication across different canid species and within domestic dogs.…”

“…Vocalisation plays a critical role in social animals for conveying information on foraging, reproductive, and social behaviours [1–7]. Characterising the vocal repertoire of a species provides a base for understanding the behavioural significance of different vocalisations and studying how vocal communication varies across the populations, subspecies, and taxa [8–10]. The wolf ( Canis lupus ) is a social mammal and uses a variety of vocalisations for communication.…”

“…The best-known wolf vocalisation – the howl – is a long-range harmonic call used for territorial advertising and social cohesion [1,16–18]. Recent studies have shown 21 different howl types across various canid subspecies based on quantitative similarity in modulation pattern [8]. Along with howl, wolves also communicate using 7 to 12 other harmonic calls, which is a clear pitch sound wave that possesses multiple integral frequencies [19–21].…”

Wolf howls encode both sender- and context-specific information

“…Hence the absence of evidence for group signatures may well be a by-product of insufficient statistical power to detect group differences. It is also worth noting that so called 'dialects' in animal vocalizations are often, although not exclusively (Elowson & Snowdon, 1994;Crockford et al, 2004;Watson et al, 2015), a consequence of genetic relatedness leading to greater within-group vocal tract similarities than between groups and, as such, more similar calls (Gouzoules & Gouzoules, 1990;Townsend et al, 2010;Kershenbaum et al, 2016). The packs at the WSC, on the other hand, are artificially composed.…”