Red squirrels use territorial vocalizations for kin discrimination

Abstract

The ability to discriminate among individuals, or among classes of individuals, can provide animals with important fitness benefits. Although several mechanisms for discrimination are possible, most require animals to show stable phenotypic variation that reflects their identity or their membership in a particular class (e.g. sex, mate, kin). For territorial animals that rarely interact physically, vocalizations could serve as long-distance signals that facilitate discrimination. In this study, we tested whether the territorial rattle vocalizations of North American red squirrels, Tamiasciurus hudsonicus, are repeatable, and whether they could hence provide the basis for multiple types of discrimination. We measured four structural features from two rattles from each of 76 marked squirrels. All four features were repeatable, which is consistent with territorial rattles being individually distinctive. We then conducted a playback experiment to determine whether squirrels use rattles for discrimination. Specifically, we tested whether squirrels discriminate between the rattles of neighbours and non-neighbours, and kin (coefficient of relatedness, r ! 0.25) and non-kin (r < 0.125). Following a 2 Â 2 factorial design, we broadcast a rattle from a non-neighbouring nonkin individual to 15 subjects, from a neighbouring nonkin individual to 14 subjects, from a non-neighbouring kin individual to 11 subjects, and from a neighbouring kin individual to 13 subjects. Subjects did not discriminate between the rattles of neighbours and non-neighbours, but did respond differently to the rattles of kin and nonkin. Specifically, squirrels were significantly more likely to produce a rattle of their own in response to the broadcasted rattles of nonkin versus the broadcasted rattles of kin. This result demonstrates that red squirrels can use territorial vocalizations for kin discrimination. It also suggests that they are more tolerant of territorial intrusions by kin.

Pectoral fin contact as a mechanism for social bonding among dolphins

“…Bruck (2013) confirmed that dolphins are capable of long-term social memory spanning decades, and other researchers have found via numerous studies that bottlenose dolphins readily recognize and react to playbacks of the signature whistles of familiar, even related, individuals (e.g., Janik, Sayigh, & Wells, 2006;King, Harley, & Janik, 2014;Sayigh, Esch, Wells, & Janik, 2007). For many species, kin recognition has been documented for aquatic mammals between mother and offspring, siblings, and second-generation relations via visual, vocal and olfactory cues (e.g., Sauvé, Beauplet, Hammill, & Charrier, 2015;Trimble & Charrier, 2011;Wilson et al, 2015), non-kin require social mechanisms or tools to establish and maintain a social relationship with a new conspecific.…”

Red squirrel territorial vocalizations deter intrusions by conspecific rivals

“…A more precise understanding of how rattles function in territory defence is still lacking. Red squirrel rattles are known to have unique signatures that allow for individual identification by other conspecifics (Wilson et al, 2015), but it is unclear if rattles will indiscriminately discourage intruders regardless of whether that rattle is from a resident or non-resident conspecific. Yasukawa (1981) suggested that one reason the speaker replacement did not deter neighbour trespass in red- winged blackbirds is because song types were used which were unfamiliar to neighbouring conspecifics.…”

“…Rattles, unlike the vocalizations of songbirds, are not known to be associated with mating and are used by both sexes. Rattles are known to have a repeatable acoustic structure that allows for individual identification and discrimination by conspecifics (Digweed et al, 2012; Wilson et al, 2015). Smith (1978) observed that red squirrels produce rattles when another squirrel enters its territory, but also periodically when there is no apparent threat.…”

Familiar neighbours, but not relatives, enhance fitness in a territorial mammal

“…Red squirrels are arboreal rodents in which both sexes defend exclusive territories (21). Territories are important for overwinter survival (22) and are defended through vocalizations called 'rattles' (23), which are uniquely identifiable (24). Following natal dispersal, individuals rarely relocate to a vacant territory (25), allowing for the establishment of 20 long-term familiarity among neighbouring individuals.…”