Northern Resident Killer Whale, Orcinus orca, Rubbing-Beach Calls
The purpose of this research was to investigate northern resident killer whale (Orcinus orca) discrete calls used during beach-rubbing behaviour. This study compared average rate of each call type used at the Main rubbing beach in the Robson Bight-Michael Bigg Ecological Reserve, Vancouver Island, to calls used at a foraging area off West Cracroft Island, BC. Discrete calls N12 and N23 were used significantly more while beach-rubbing. The N16 call type was used significantly more while foraging. Killer whale discrete call repertoires identify family groups. This study shows that certain call types can be emitted more frequently during specific activities. Change in killer whale call rate could influence behaviour and maintain group synchronism.
Delphinidae, Killer whale, Orcinus orca, behaviour, vocal repertoire, discrete calls.
Orcinus orca is a cosmopolitain species living in all the world’s oceans. Killer whales are toothed whales and the largest member of the dolphin family Delphinidae. Killer whales live long, have long gestation periods, and care for their offspring. Individual populations of killer whales often specialize in particular prey types. There are three populations, or ecotypes, of killer whales in British Columbia. The transient population feed on marine mammals, the offshore population forages on fish and sharks along the continental shelf (Fisheries and Oceans Canada 2016), and residents prey on fish particularly Chinook salmon, Oncorhynchus tshawytscha (Ford and Ellis 2005). These populations are different morphologically, acoustically, and genetically (Barrett-Lennard 2000). Two sympatric populations of resident killer whales live in northern and southern BC. In total, there are four communities of killer whales in BC Bigg’s a.k.a transient, offshore, and northern and southern resident. Threats to these animals include decline in prey availability, noise, effects from marine vessels, oil spills, and persistent organic pollutants (Grant and Ross 2002).
Resident female killer whales live on average for 50 years and males for 29 respectively (Ford et. al. 2000). Male killer whales can live up to 60 years old. Matriarchs can live for over a 100 years old and are important members of each family group. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) lists British Columbia’s killer whale communities as Threatened (Bigg’s), Special Concern (offshore), Threatened (northern resident), and Endangered (southern resident).
Killer whale vocalizations are made up of echolocation clicks, whistles, and discrete calls. Killer whale populations can be identified by their vocal repertoires (Ford et. al. 2000, Ford and Fisher 1983). Each matriarchal group has an acoustic badge consisting of an average of ten discrete call types (Ford 1991). Structure and use of killer whale calls suggests they serve as contact signals to maintain family cohesion (Ford 1991). Offspring seem to acquire calls through vocal learning (Crance et. al. 2014, Foote, et. al. 2006, Bain 1989). Discrete calls contain abrupt shifts in pitch and wide-band energy content. Variations in stereotyped calls can increase when in close proximity while visual and physical contact is possible. After group separation modification to call signal structure can reflect emotional state and reaffirm relationships (Ford 1991). All calls are used during most killer whale activities (Ford 1989).
Resident killer whale societies are made up of matrilineal groups consisting of a mother and her descendants. Residents remain with their natal groups their entire lives maintaining stability of discrete calls. Related family groups travel together creating pods. The vocal system of residents could allow them to avoid inbreeding by selecting dissimilar mates from other family groups. Increasing group diversity promotes population fitness and survival. Pods that share certain calls form acoustic clans (Ford 1991). These acoustic clans are genetically distinct maternal lineages (Yurk et. al. 2002). Call repertoires of matrilineal groups are a result of cultural transmission (Yurk 2005). The southern resident community is made up of one acoustic clan; J-clan. The northern resident community is made of three acoustic clans; A, G, and R clans.
Swimming close to shore and rubbing on beach pebbles is a behaviour known exclusively to the northern resident community of killer whales. Ford (1989) found the N3 and N12 calls emitted more frequently during beach-rubbing and socializing activities. This study investigated recordings of the northern residents made by OrcaLab (orcalab.org) volunteers and researchers at the Main rubbing beach, Robson Bight-Michael Bigg Ecological Reserve, to calls used at a foraging area, Cracroft Point (Figure 2). Average rate of each discrete call type used while beach rubbing and foraging were compared. The null hypothesis was (Ho) there is no difference in call rate while beach-rubbing compared to foraging behaviour. The alternative hypothesis was (Ha) there is a difference in call rate while beach-rubbing compared to foraging behaviour. Understanding how killer whales use vocalizations to maintain group cohesion can increase our knowledge to protect critical marine environments.
METHODS & MATERIALS
Northern resident killer whale discrete calls were analyzed through OrcaLab (orcalab.org) recordings on the Orchive database (orchive.cs.uvic.ca). OrcaLab observation log books were referenced for direction, location, and identification of whale groups. Vocalizations were annotated, classification of calls were determined aurally and visually through spectrogram analysis of side-band intervals, call length, and vocalization structure. Catalogues of killer whale calls were used to determine discrete call type classification from Ford (1987) and the Orchive. Average use of each discrete call type per recording was compared between the Main rubbing beach (R B) and Cracroft Point (CP) foraging area. Statistical t-tests were used to determine any significant difference in average call rate.
Random recordings from 2004 to 2006 were analyzed. A total of 2,096 calls were identified (46 recordings, total 4,140 min). Discrete calls used at the Main rubbing beach and foraging area off Cracroft Point included N1, N2, N3, N4, N5, N7, N9, N12, N13, N16, N23, N24, and N25. The average rate of each discrete call type category used at the Main rubbing beach (RB) and Cracroft Point (CP) was compared. There was a significant difference in call production for the N12 and N23 discrete call types being used more on average at the Main rubbing beach than at Cracroft Point (p<0.05). The N16 call type was used significantly more while foraging than during beach-rubbing behaviour (p<0.05). Discrete call types N2, N4, N7, and N13 were used marginally insignificantly more while foraging than during beach-rubbing activity. Call type N25 was used marginally insignificantly more while beach-rubbing. There was no significant difference found in emission rate for other call types (p>0.25).
This study revealed northern resident killer whale (Orcinus orca) call frequency during beach-rubbing and foraging behaviour. Change in call rate may indicate specific killer whale activities and behaviours. I hypothesized that this population of killer whales may use certain calls while beach-rubbing. Discrete call types N12 and N23 were used significantly more during beach-rubbing behaviour than while foraging. This study supports Ford’s (1989) findings that the northern residents use discrete call N12 significantly more while beach-rubbing than during foraging behaviour. Discrete call type N16 was used significantly more while foraging compared to beach-rubbing activity.
Rubbing on beach pebbles is a unique behaviour known globally only to the northern resident killer whale population. Acoustic repertoires identify killer whale family groups. Change in call rate could help coordinate their actives and promote group cohesion. The N12 and N16 call types are used by A-clan whales while the N23 call is part of the G-clan vocal repertoire (Ford 1987). Increase in emission rate of calls N12 and N23 may indicate beach-rubbing behaviour for the A and G clans respectively. Call type N16 could represent an increase in foraging activity for A-clan whales.
Change in killer whale call rate could signal different behaviours. Further research is needed to investigate northern resident discrete calls used at other rubbing beaches. Examining killer whale vocalizations during other specific behaviours like the southern resident greeting ceremonies could help determine if change in call rate is consistent with distinct activities. Acoustic communication is an important method for killer whale societies to coordinate and maintain contact. Killer whale populations have unique vocal and behavioural traditions that deserve protection and require preservation. This research provides knowledge on killer whale vocal behaviour during group activities and increases awareness of critical marine environments.
We would like to thank the assistants at OrcaLab for their observations and recording efforts. This study could not have been possible without OrcaLab volunteers, Johnstone Strait killer whale researchers (Dr. Michael Bigg, John Ford, and Graeme Ellis), and the whale-watch community.
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