First insights into the vocal repertoire of infant and juvenile Southern white rhinoceros

Abstract

Describing vocal repertoires represents an essential step towards gaining an overview about the complexity of acoustic communication in a given species. The analysis of infant vocalisations is essential for understanding the development and usage of species-specific vocalisations, but is often underrepresented, especially in species with long inter-birth intervals such as the white rhinoceros. Thus, this study aimed for the first time to characterise the infant and juvenile vocal repertoire of the Southern white rhinoceros and to relate these findings to the adult vocal repertoire. The behaviour of seven mother-reared white rhinoceros calves (two males, five females) and one hand-reared calf (male), ranging from one month to four years, was simultaneously audio and video-taped at three zoos. Normally reared infants and juveniles uttered four discriminable call types (Whine, Snort, Threat, and Pant) that were produced in different behavioural contexts. All call types were also uttered by the hand-reared calf. Call rates of Whines, but not of the other call types, decreased with age. These findings provide the first evidence that infant and juvenile rhinoceros utter specific call types in distinct contexts, even if they grow up with limited social interaction with conspecifics. By comparing our findings with the current literature on vocalisations of adult white rhinoceros and other solitary rhinoceros species, we discuss to which extent differences in the social lifestyle across species affect acoustic communication in mammals.

Proximity-based vocal networks reveal social relationships in the Southern white rhinoceros

“…Even though there was a clear sex-specific difference in overall Pant rates between male and female senders, we could only find a trend in the effect of dyad type, indicating that female senders showed no preference for either sex of the potential receiver. Therefore, our results support the previous descriptions of Pant, as it appears to function as both, a socio-positive cohesive call type especially for the females 52,53,63,64 as well as a mating call for the males 46 .…”

“…In addition to their very pronounced olfactory sense, SWR have a distinct vocal repertoire with ten to eleven different call types 46 , 52 , of which the most common call types in adult animals are Hiss, Grunt, Pant and Snort (in previous publications Hiss has been termed Threat, but in order to be consistent all call types are labelled onomatopoeically from here on). Whereas Hiss and Grunt are uttered exclusively during agonistic interactions, Pants seem to function as contact as well as mating calls, while Snorts are mainly uttered during resting and feeding 46 , 52 , 53 . Despite the well depicted vocalisations, determining communication structures in SWR groups still poses a challenge with regard to the identification of vocal interaction partners, as the majority of obvious reactions to approaching conspecifics or vocalisations are only observed during infrequent high-intensity encounters such as fighting or mating 50 .…”

“…Vocalisations were detected by auditory identification and categorised according to the literature 46,52,53 . For each vocalisation, the respective call type and sender were noted.…”

An unexpected acoustic indicator of positive emotions in horses

“…prior to the beginning of suckling in squirrel monkeys: [ 112 ]). Snorts have been previously described in some perissodactyls during positive contexts, either while foraging (rhinos:[ 33 , 113 ]) or again during short distance communication between a mother and her young (while licking) as “an appeasement call” (tapirs: [ 34 ]). Kiley [ 37 ], in a detailed study on Ungulates vocalisations, proposed an acoustic gradient following an excitement gradient which included both non-vocal and vocal sounds.…”

Rutting vocal display in male impala (Aepyceros melampus) and overlap with alarm context

“…A particularly remarkable trait of male impala rutting vocal display is pant-roaring with a rapid alternation of inhalatory and exhalatory vocalization phases [ 14 – 16 , 18 ]. Pant-calls are also reported for two species of marsupials [ 46 – 48 ], two species of rhinos [ 49 – 51 ] and three species of primates [ 52 – 55 ]. Potentially, and in addition to low fundamental and formant frequencies, the rapid alternation of inhalatory and exhalatory phases in male impala rutting calls may function as a further acoustic trait of male quality in harem-holding mammals.…”