![]() Doppler shift is the change in frequency of a wave that arises from relative motion between the source and the receiver of the wave. Here we investigate the Doppler effect as an additional explanation for some of the intra-annual patterns in observations of tonal frequency. However, they considered that such an explanation was not likely to apply to the long-term trend and suggested that changes in whale vocal behaviour remained the most parsimonious explanation for the long-term inter-annual decline. They suggested that this decrease in depth could arise from changes in dive behaviour over the length of each season, or that it could be due to other factors such as variations in water temperature or change in blubber mass. proposed that the mechanism behind the intra-annual pattern ( Figure 2) might be explained by a gradual decrease in the depth at which songs are produced. However, presently there are not enough estimates of the source level of calls (let alone population density) of Antarctic blue whales to test whether source levels have decreased in a manner similar to that predicted by McDonald et al. A key driver of this theory was that the source levels required for whales to keep in acoustic contact with a constant number of conspecifics would not have to be so high if population density were increasing. They concluded that the most likely explanation of the trend was related to increasing population density, and suggested that the tonal decline was an anatomical constraint of the mechanism of sound production that also resulted in a decreased call source level. discussed a number of hypotheses for the long-term inter-annual decline, including changes in population structure, ambient noise, physical environment, and whale behaviour. Copyright 2012 Journal of the Acoustical Society of America, American Institute of Physics. Long-term trend and intra-annual pattern in tonal frequency of Antarctic blue whale calls. Long-term and intra-annual trends in tonality of Antarctic blue whale song. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist.įigure 2. ![]() This work was supported by the International Whale and Marine Mammal Conservation Initiative of the Australian Government via Southern Ocean Research Partnership of the International Whaling Commission. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.įunding: Deployment of long-term recorders was supported by the Australian Antarctic Division. Received: MaAccepted: AugPublished: September 17, 2014Ĭopyright: © 2014 Miller et al. PLoS ONE 9(9):Įditor: Jean-Benoit Charrassin, Musee National d′Histoire Naturelle, France However, data do show cyclical changes in frequency in conjunction with season, thus suggesting that there might be a relationship among tonal frequency, body condition, and migration to and from Antarctic feeding grounds.Ĭitation: Miller BS, Leaper R, Calderan S, Gedamke J (2014) Red Shift, Blue Shift: Investigating Doppler Shifts, Blubber Thickness, and Migration as Explanations of Seasonal Variation in the Tonality of Antarctic Blue Whale Song. Furthermore, analysis of intra-annual frequency shift at Antarctic recording stations indicates that the Doppler effect is unlikely to fully explain the observations of intra-annual pattern in the frequency of Antarctic blue whale song. Results from vessel-based recordings of Antarctic blue whales indicate that variation in peak-frequency between calls produced by an individual whale was greater than would be expected by the movement of the whale alone. The assumptions and implications of the Doppler effect on whale song are investigated using 1) vessel-based acoustic recordings of Antarctic blue whales with simultaneous observation of whale movement and 2) long-term acoustic recordings from both the subtropics and Antarctic. An additional hypothesis that has not yet been investigated is that differences in the observed frequency from each call are due to the Doppler effect. While a number of hypotheses for this long-term decline have been investigated, including changes in population structure, changes in the physical environment, and changes in the behaviour of the whales, there have been relatively few attempts to explain the intra-annual pattern. Measurements of these calls from recordings spanning many years have revealed a long-term linear decline as well as an intra-annual pattern in tonal frequency. The song of Antarctic blue whales ( Balaenoptera musculus intermedia) comprises repeated, stereotyped, low-frequency calls.
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