Dawn M. Grebner 1 – dmg302@psu.edu
David L. Bradley 1, Dean E. Capone 1, Susan E. Parks 1,
Jennifer L. Miksis-Olds 1 and John K. B. Ford 2
1Graduate Program in Acoustics, Penn State University, State College, PA, USA 16804
2 Pacific Biological Station, Nanaimo, BC, V9T 6N7, CA
Popular version of paper 3aAB11
Presented 11:05 a.m. on Wednesday, November 12, 2008
156th ASA Meeting, Miami, FL
This study examined vocal exchange behavior when mother killer whales were separated from at least one of their offspring (juvenile(s) and/or calf).
Fish-eating killer whales, known as Residents in the Pacific Northeast waters off British Columbia and Washington State, regularly associate with one another in pods. Pods consist of related individuals and can be further subdivided into matriarch-led family groups known as matrilines. Matrilines can contain anywhere from 1 to 4 generations including the matriarch, her adult male and adult female offspring, and her daughters’ offspring and grand-offspring. These associations are life-long.
Since killer whale matrilines are stable and remain together for life, vocal exchanges are an important means of communication and an excellent opportunity for vocal learning. Killer whale discrete pulsed calls are abundant and stable with each pod having its own repertoire or dialect. Young killer whales would not only need to recognize their mother’s vocalizations, they would also need to learn their pod’s repertoire in order to survive. A mother with her young and sub-adult offspring, are a tight social group where young killer whales are thought to learn the vocal and behavioral skills they will need later on as adults.
It is in the early stages of a mammal’s life that it is introduced to group vocalizations and behavioral skills which will later be necessary to maintain group cohesion. For other toothed whale species such as bottlenose dolphins, calves are thought to learn their unique whistle within the first year of life. Killer whale offspring often spend the majority of their daily time relatively close to their mothers. Physical swimming distances between offspring and their mothers increases with age. Newborn calves swim at their mothers’ sides while the oldest offspring swims the farthest away.
In order to isolate an individual’s vocalizations, sounds were localized using three hydrophones (underwater microphones) arranged in a triangle which were mounted to the seafloor in Johnstone Strait, B.C. during summers 2006 and 2007. A surveying instrument called a theodolite was used to track the killer whales’ positions as they swam by the array. Behaviors, group composition and animal movement patterns were collected on top of a 50 meter cliff located above the submersed hydrophone array. Animals were identified from still photos, a video camera, and a high resolution scope using an ongoing photo-identification catalog of killer whale saddle patches and dorsal fins. Killer whales can be identified by the shape of their saddle patch which is the gray region on their backs behind their dorsal fins, and also by any distinctive markings (or nicks) on the dorsal fin. A picture has been provided which shows a foraging mother (name, A52) on the left with her three-year-old (A81, on the right) swimming nearby. In addition to her unique saddle patch, A52 has two distinctive nicks on the backside of her dorsal fin (see top and middle).
This analysis was divided into two categories: matched call-types (one animal produced a pulsed call and one or more animals repeat that same sound) and then initiated calls with their responses (both matched and mixed (non-identical)).
Matched call-types
Match calling was first identified in vocal exchanges between a few killer whales in a previous study. In this study it was found that match calling was present when mothers were separated from one of their offspring. This result was seen for all five pods recorded in this study.
Multiple pulsed calls were matched in each pod’s repertoire. One noticeably abundant matched pulsed call was the N04, which is produced exclusively by the A1, A4 and A5 pods. The N04 call was separated into different variations and it was found that they were produced in equal proportion. However, variations of N04 appear to be disproportionately produced during traveling and foraging behaviors. This raises the question as to whether killer whales are shifting the frequency and time information within the N04 call to relay their current or changing behavioral state to other pod members.
Initiated calls and responses
Calves, young juveniles, older juveniles and mothers were found to all initiate pulsed calls in instances where a mother was separated from one or more of her offspring. Responses to the initiator’s vocalizations were produced by all age groups. Mothers and calves initiated calls more often than they responded, while juveniles initiated calls slightly more than other age groups.
The success of localizing calf vocalizations was low. A social dynamic of killer whale matrilines is that calves usually spend most of their time at their mothers’ sides, rarely venturing off too far. It is very difficult mathematically to accurately isolate the vocalizations of two very closely spaced individuals using an array. This study, however, was able to localize some calf vocalizations. There may be a certain age that calves begin to briefly separate from their mothers. This age may depend on the individual; that is some individuals may naturally be more adventuresome at an earlier age than others or perhaps, the presence of an older sibling swimming farther from the mother may influence the calf to temporarily leave its mother side.
Main references
Bigg, M. A., Olesiuk, P. F., Ellis, G. M., Ford, J. K. B. & Balcomb, K. C., III. 1990. Social organization and genealogy of resident killer whales (Orcinus orca) in coastal waters of British Columbia and Washington State. Reports of the International Whaling Commission. Special Issue No. 12: 383-406.
Ellis, G. M., Ford, J. K. B. & Towers, J. R. 2007. Northern Resident killer whales in British Columbia: photo-identification catalogue 2007. Fisheries and Canada : Pacific Biological Station,. 1-41.
Ford, J. K. B. 1991. Vocal traditions among resident killer whales (Orcinus orca) in coastal waters of British Columbia. Canadian Journal of Zoology. 69: 1454-1483.
McCowan, B. & Reiss, D. 1995. Whistle contour development in captive-born infant bottlenose dolphins (Tursiops truncatus): wide-band, low-frequency signals during mother/aunt-infant interactions. Zoo biology. 14: 293-309.
Miller, P. J. O., Shapiro, A. D., Tyack, P. L. & Solow, A. R. 2004. Call-type matching in vocal exchanges of free-ranging resident killer whales, Orcinus orca. Animal Behavior. 67(6): 1099- 1107.