Maybe they've been listening to Barry White...

Male whales are singing lower.

The researchers speculate that in the heyday of commercial whaling, as blue whale numbers plummeted, it may have been advantageous for males to sing higher frequency songs in order to maximize their transmission distance and their ability to locate potential mates. But as population sizes have increased, it may now be more advantageous for males to sing songs that are lower in frequency rather than louder. "When they make these songs they need to use most of the air in their lungs," said Hildebrand. "It's like an opera singer that sees how long he can hold a note." [More]

Hey, baby...