1 Department of Biology, Faculty of Science, SDU2 Faculty of Science, SDU3 Department of Biology, Faculty of Science, SDU
presented by Outi at: Acoustic Communication by Animals, 2nd International Conference, August 12-15, 2008, Oregon State University, Corvallis, Oregon, USAAnnual changes in the song of the bowhead whale Balaena mysticetusin Disko Bay, Western GreenlandOuti Tervo and Mads F. Christoffersen, Arctic Station, University of Copenhagen, Qeqertarsuaq, Greenland, firstname.lastname@example.orgSusan E. Parks, Applied Research Laboratory, Pennsylvania State University, State College, PA, USAReinhardt M. Kristensen, Zoological Museum, Natural History Museum, University of Copenhagen, DenmarkLee A. Miller, Institute of Biology, University of Southern Denmark, Odense, DenmarkBowhead whale Balaena mysticetus acoustic behaviour has been a target of several investigations, primarily from recordings of the Bering Sea population near Alaska (Ljungblad et al 1980, Clark and Johnson 1984, Cummings and Holliday 1987) with a few studies recording sound from the Davis Strait population (Richardson et al 1995, Richardson and Finley 1989). Songs have been recorded from bowhead whales during their spring migration off Point Barrow when the whales were returning from their breeding grounds and swimming towards their feeding areas (Ljungblad et al 1982, Clark and Johnson 1984, Cummings and Holliday 1987). Winter vocal behaviour of the species has been poorly documented although it has been suggested that bowhead whales produce a large variety of sounds during this time (Würsig and Clark 1993).Consequently, the goals of this study were to record the sounds of bowhead whale in Disko Bay, Western Greenland, to describe the vocal repertoire of the Davis Strait stock during winter and spring, and to study the annual changes in the song they produce. The acoustic data were collected in three subsequent years: February - May 2005, April 2006 and February -May 2007. Recordings were made using two hydrophones deployed through holes in the ice or from a small dinghy in an area where bowhead whales were seen.The vocal signals recorded in this study were divided into simple frequency modulated (FM) calls (n= 523), complex amplitude modulated (AM) calls (n=659) and song notes (n=4394). All call types were present in the repertoire each year. Songs were composed of repetitive units referred here as song notes and were the most frequently documented type of vocalisation every year. Song notes had a stereotyped frequency contour and formed trains of signals that could be grouped into phrases and themes. The analyses of the song concentrated on describing the song notes in order to capture small scale and subtle differences. The variables used in the song note analyses were duration, minimum frequency, maximum frequency, frequency range, start frequency, end frequency, number of inflection points and number of modulation points. The sex of the singer was unknown.Using visual and audio inspection, song notes were further divided into a priori song note types and this classification was verified using multinomial log-linear analysis. According to the model, eight song note types could be distinguished for the year 2005 and three song note types for each of the following years 2006 and 2007. The highest percentage score in each type, ranging from 52.8% to 100%, was the result of the self test indicating a greater variation between types than within types. Although some mixing between song note types occurred, 94.8 % of the song notes analyzed (n=4168) were classified consistently with the a priori classification when using the eight variables. (A table will be presented at the meeting.)The song of the bowhead whales in Disko Bay changed from year to year as previously documented for the bowhead whales of the Bering Sea population (Clark and Johnson 1984). The song of the bowhead whales in Disko Bay was composed of a new set of song notes each year. This can be due to annual changes in the composition of individuals that are present in Disko Bay each season. However, it is more likely that sexual selection drives the changes in the song of the bowhead whales like it has been suggested for humpback whales (Tyack 1981). Disko Bay is an aggregation area for adult animals and new visual observations of sexual behaviour together with the presence of a complex song described in this study support the hypothesis that the Qeqertarsuaq area serves as a mating ground for bowhead whales.