Assuming the data are correct, the explanation (while not impossible) seems slightly implausible. Beyond the range of visibility, how would the males know there were fewer females listening and so adjust their singing?

Have the authors considered other simpler hypotheses? I would like to know firstly "Do different animals sing in different ways, as perhaps older more mature males sing at lower tonal frequencies than their younger counterparts?" and "How has the increase in numbers changed the age profile of the population?"

Interesting article.
To 'Anonymous', a simpler hyothesis?
I read an article some months ago, describing how the change in pitch of whale song was a simple adaption. I remember that undersea drilling was given as one example of manmade noise in the oceans, with which whales have to compete with to make their song heard by others.
Boat engine noise comes to mind, sonar too.
I am afraid I did not bother to remember the detail of the article I read. The explanation was simple and elegant however, whales are changing the pitch of their song for a very simple reason..... to have some chance of being heard above the cacophony of manmade noise.

Re : Simpler hypotheses

That the whales are adapting their behaviour to overcome noise pollution is certainly a simple and appealing hypothesis. Given the reproductive rate and life span of whales though I would be sceptical that such changes could be the result of Darwinian adaption, even if those with the most audible song might breed more successfully.
So to be credible it would require the whales to change behaviour. That could well be the case. These wonderful creatures show signs of real intelligence. I guess I just like to rely on Occam and examine the simplest ideas first.

Wow, I am truly surprised by the last three comments posted. Being someone from a small town of Blackstone, Massachusetts, I am always defending the U.K. citizens as being more "empirical" or intellectual than us Americans, and though this statement may be oxy-moronish I must go on:
Though I cannot assume the country of origin of any of the previous commentators, did any of you read the article above that I did?
I gathered that the blue whales have been able to lower their frequencies and revert back to their natural tones due to the cease in hunting them. As stated by Mr. Hawkes, "Instead of having to shriek at the top of their voices . . . they can now sing . . . in a lower and more natural key."
The first comment states, "how would the males know there were fewer females listening and so adjust their singing?"
Are you serious??? That is not at all what was hypothesized by the above referred to study.
The second commentator says, "I remember that undersea drilling was given as one example of manmade noise in the oceans, with which whales have to compete with to make their song heard by others . . . whales are changing the pitch of their song for a very simple reason..... to have some chance of being heard above the cacophony of manmade noise."
Again, the writer of this article is stating the whales are able to communicate with each other without having to use the higher, more long-distant frequencies they were using before.
The third comment is not as offensive . . . but anyone reading this please tell me what I am missing.
I simply stumbled upon this web-article by Nigel Hawkes, but am I the only one that reads these comments and can see their point, but how they are not logistically an argument against what is stated in the article above???
They all make valid points, but sound as though they are fighting with other data and not the article presented!!!!!

I'm struggling to see the concerns of Sasha White. The comments are not claiming that Mr Hawkes is wrong they are simply asking if there are alternative hypotheses. That is the way science progresses - by setting up competing hypotheses and seeing which better explains real world observations.

The first contribution seems a good hypothesis because it is testable. It should be possible to record individual whale song, and then see if the older whales sing at different tonal frequencies. This might be done by looking at a group of whales of varying ages, or perhaps if any individual whales are tagged or recognisable recording their song at intervals as they get older and seeing if it changes.

If age is found to have no influence on tonal frequency then this hypothesis would fall, and could be rejected. But if the hypothesis passes these tests then confidence that it is the true explanation would be considerably increased.

I don't find either comment offensive. They are simply questioning. I don't feel Mr Hawkes would be upset either - while his explanation may be the correct one, I do not feel it is yet proven. The data demonstrate with absolute clarity that the observed change in average frequencies is real. The question is why?