The Blue whale–the largest animal ever to inhabit our planet–has been tracked by researchers since its numbers were perilously close to extinction in the 1960’s. Much of this tracking has been accomplished through underwater monitoring of whale “songs”, which are sung exclusively by male whales. These long, and fairly complex, sonic compositions are believed to be the means by which these whales attract mates. Over the past several years, the world’s blue whales have begun singing a different tune, of sorts; the frequency range of their songs has gotten significantly lower. And, this is happening, “in concert” all over the world–where ever these massive Cetacea migrate, feed, congregate and mate.
Sound–whether produced by natural or artificial means–is carried on “waves” (self-propagating, periodic disturbances in a conducting medium) and is measured in frequency units called Hertz’s (cycles per second; 1 Hz = 1 cycle per second). Most whales and their smaller “cousins”, dolphins, normally communicate at very high frequencies–far above the 20, 000 Hz range limit of human hearing. In fact, the vocalizations made by captive whales and dolphins (e.g., at marine parks) are selected by the animal; the marine mammals are not trained to vocalize in this range, but know that this is the range humans communicate in (see Lilly, J. , Communication between Man and Dolphin). Whales can produce sound waves in the 120, 000 Hz range and above.
Scientist are puzzled as to why these blue whales (Balaenoptera musculus) are using this much lower “frequency band”. Some have speculated that they are competing with communication noise from increased shipping in there territories. However, this explanation does not satisfy scientists. According to marine mammal researchers, there is far more electromagnetic “noise” at the lower end of the spectrum, than at the higher end.
Other possibilities have to do with whale population increases. In former days when their numbers were quite small, the whales had to communicate (to attract mates) over much larger distances (note: higher frequency sound waves travel much further than shorter ones). Thus, according to the theory, as their number rebounded, there resulted less of a need for high frequency (Hz) singing, since a possible mate was probably much closer by.
But even this does not satisfy many scientists. Reproductive needs (such as attracting a mate) should take priority here, and since these animals are dealing with an increasingly noisy ocean environment, this would be an impetus for higher band communications, not lower, as is happening, and further: high frequency sound waves are also, potentially, much louder.
The evidence for lower frequency songs in male blue whales (which are of a type of whale known as mysticene, or baleen, whales) was compiled and brought to light in a paper by private oceanographer Mark McDonald, along with co-authors John Hillebrand (of the Scripps Institute) and Sarah Mesnick (of NOAA), recently published in the journal Endangered Species Research
Read the original January 24, McClatchy new story by Renee Schoof.
Read the paper: Wold wide decline in tonal frequencies in blue whales (McDonald et al)