Stability and group specificity of stereotyped whistles in resident killer whales, Orcinus orca, off British Columbia

Abstract

Resident killer whales off British Columbia form four acoustically distinct clans, each with a unique dialect of discrete pulsed calls. Three clans belong to the northern and one to the southern community. Resident killer whales also produce tonal whistles, which play an important role in close-range communication within the northern community. However, there has been no comparative analysis of repertoires of whistles across clans. We investigated the structural characteristics, stability and group specificity of whistles in resident killer whales off British Columbia. Acoustic recordings and behavioural observations were made between 1978 and 2003. Whistles were classified spectrographically and additional observers were used to confirm our classification. Whistles were compared across clans using discriminant function analysis. We found 11 types of stereotyped whistles in the northern and four in the southern community with some of the whistle types being stable over at least 13 years. In northern residents, 10 of the 11 whistle types were structurally identical in two of the three acoustic clans, whereas the whistle types of southern residents differed clearly from those of the northern residents. Our study shows that killer whales that have no overlap in their call repertoire use essentially the same set of stereotyped whistles. Shared stereotyped whistles might provide a community-level means of recognition that facilitates association and affiliation of members of different clans, which otherwise use distinct signals. We further suggest that vocal learning between groups plays an important role in the transmission of whistle types.

Orchestration : the movement and vocal behavior of free-ranging Norwegian killer whales (Orcinus orca)

“…Although no definitive study has been conducted demonstrating vocal learning in killer whales, several separate observations support both this conclusion (Bowles et al, 1988;Foote et al, 2006;Nousek et al, 2006;Riesch et al, 2006) and that cultural transmission may be the mechanism underlying development and acquisition of the vocal repertoire. Ford (1991) suggested that when pods become too large to afford all members adequate access to resources, they splinter into two or more smaller pods and acoustic dialects begin to diverge slowly through cultural drift whereby changes arise from small copying errors in vocal imitation and transmission.…”

Bat echolocation calls facilitate social communication

“…In many taxa, acoustic signals encode social information about the sender, such as sex [2], age [3], size [4], reproductive status [5], group affiliation [6], or individual identity [7]. However, it is often unclear whether social information encoded in vocal signatures is voluntarily or involuntarily shared with conspecifics [1], and whether shared information is actually used by receivers [8,9].…”

Whistle communication in mammal-eating killer whales (Orcinus orca): further evidence for acoustic divergence between ecotypes

“…Such acoustic 65 signals have been defined as private and they are usually rather quiet, comparatively high 66 in frequency, and highly modulated in order to be more prone to attenuation andsuch ultrasonic whistles did not occur in recordings of North Pacific residents or 114 transients. Although the vast majority of resident whistles seem to be variable in nature, 115 several stereotyped whistle types have been described that are often emitted in complex 116 sequences (Riesch et al 2006(Riesch et al , 2008. Compared to pulsed calls, killer whale whistles 117…”

“…A priori probabilities were calculated based 242 on group-sizes, and these were then used to calculate the proportional-by-chance 243 accuracy by summing the squares of all prior probabilities. An overall classification 244 success for the model was provided, and the grouping variable was stereotyped whistle 245 category ('TW1', 'TW2', or 'TW3').resident killer whales from a previous study (Riesch et al 2006), and tested for 248 differences between stereotyped whistles of different killer whale populations by means 249 of a full-factorial multivariate GLM (MANOVA). The dependent variables were again z-250 transformed whistle parameters, and population ('transient', 'northern resident' or 251 'southern resident') was the fixed factor.…”

“…Variable whistles, on the other 142 hand, did not have stereotyped contours and were thus only found once and in a single 143 recording. We named stereotyped whistles alphanumerically as TW1 (transient whistle 144 type 1), TW2, and so on (see also Riesch et al 2006Riesch et al , 2008 observers. All whistles were printed on separate 8 x 10 cm sheets, and spectrograms were 176 presented in a random order.…”