Blue whales singing with deeper voices

Dec 08, 2009 by Lin Edwards weblog
Photo: Fred Benko - National Oceanic and Atmospheric Administration (NOAA) Central Library. (via Wikimedia Commons)

(PhysOrg.com) -- Blue whales, the largest animals on earth, are singing with deeper voices every year, but scientists are unsure of the reason.

Whale Acoustics is a company that specializes in recording the songs of blue whales off the coast of California. According to their President, Mark McDonald, they have many recordings of blue whales, but each year they have had to recalibrate their detectors to lower frequencies. Possible reasons include noise at sea, new mating strategies, and changing , but none of these theories is convincing.

McDonald, along with John Hildebrand and Sarah Melnick of the Scripps Institution of Oceanography, have collected and analyzed thousands of recordings of blue whales from the 1960s onwards, from populations around the globe, and have found the tonal frequency of the songs has reduced by fractions of a Hertz every year. This has been true even though the songs differ in different oceans and the populations seem quite distinct from each other. In the most studied populations, those off California, the pitch has reduced by 31 percent during the period.

McDonald originally thought the cause could be more noise pollution in the oceans through increased shipping traffic, since it is known that ambient noise in the oceans has increased by over 12 decibels in the last fifty or sixty years. However, McDonald said that if whales were trying to be heard above increased ambient noise, they would be expected to sing at higher frequencies rather than lower.

Another possibility is that sounds travel differently through water that is now warmer, more acidic, and contains more absorbed carbon dioxide than before, and the whales are responding to the changes. McDonald said he doubts this is the cause since the effects are so small, and the shift in frequency is relatively large.

Blue whales were hunted almost to during the early twentieth century, and since hunting has stopped populations are recovering, and it has been suggested that the songs were higher pitched in the 1960s than they are now because they needed their songs to be louder to reach the more scattered populations. The problems with this idea are populations that were not hunted have also lowered the frequency of their songs, and low frequency sounds are known to travel further than high frequencies.

Another possible reason for the lowering of frequency may be connected with selection of mates, since only male blue whales sing, and larger, more mature whales tend to sing at lower frequencies. The hypothesis is that younger males may be trying to impress females by emulating their seniors, but little is known about how blue whales use their songs, and their social dynamics are poorly understood.

The research paper was published in the October edition of Endangered Species Research.

More information: McDonald MA, Hildebrand JA, Mesnick S, Worldwide decline in tonal frequencies of songs, ESR 9:13-21, Full text in pdf format

© 2009 PhysOrg.com

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User comments : 8

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A_Paradox
4.7 / 5 (3) Dec 08, 2009
I find this article rather interesting but I think some obvious questions have not been addressed. One is this: the blue whale population was devastated by whaling. As the world wide population has increased again after cessation of the killing, does this not mean that the average age of the singing population went down when the recovery began? That seems reasonable to me, with a corollary that the average size of singing males went down also but now the average size is increasing as the population of survivors increases. By and large, bigger animals have lower voices than smaller animals of the same species.
denfire
3 / 5 (2) Dec 08, 2009
it could be that they have had to result to deeper tones bc of noise pollution in the sea caused by large ships... this would prevent these ultra social animals from communicating across long distances.... hence they have had to use lower tones in order to be heard by neighboring whales... the lower the frequency the longer distances the sound can travel through water medium.... maybe? comments anyone?
megaskins
3 / 5 (2) Dec 08, 2009
...or maybe they are taking anabolic steroids...just sayin'...
deatopmg
1.5 / 5 (2) Dec 08, 2009
A_Paradox's above comments are the obvious answer to the mystery. One totally overlooked by the authors but they were creative (dogmatic?) enough to bring up the silly notion "that sounds travel differently through water that is now warmer, more acidic, and contains more absorbed carbon dioxide than before, and the whales are responding to the changes." Are they operating off of a global warming grant?

Or maybe the increased CO2 is just irritating the whales vocal cords, making them hoarse and lowering the pitch of their sounds.

This is NOT Scripps quality work!
danman5000
5 / 5 (1) Dec 08, 2009
@denfire: Your exact questions were answered in the article, if you read it.
McDonald originally thought the cause could be more noise pollution in the oceans through increased shipping traffic, since it is known that ambient noise in the oceans has increased by over 12 decibels in the last fifty or sixty years. However, McDonald said that if whales were trying to be heard above increased ambient noise, they would be expected to sing at higher frequencies rather than lower.
vanderMerwe
not rated yet Dec 09, 2009
How much warmer?
How much more acidic?
How much more dissolved carbon dioxide?

This piece is politically correct pure speculation.
Bob_B
not rated yet Dec 09, 2009
If their population has been slaughtered so badly perhaps their singing is of the weeping/wailing which could tend to be lower, perhaps like our sobs...?
PinkElephant
not rated yet Dec 09, 2009
A_Paradox's above comments are the obvious answer to the mystery. ...


No they are not, since the article also includes the following statement:

The problems with this idea are populations that were not hunted have also lowered the frequency of their songs...


It seems both you and A_Paradox need to work on your attention focus and/or reading comprehension.

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