Deep Bue Whales

From NYT -
Scientists believe that the mating call of the Blue Whale, the world's largest animal, has begun to decrease in pitch, up to %30. The whales are thought to have departed from their higher frequency routine after populations have recovered since whaling was banned. The higher frequencies were necessary to find mates when mates were sparse.
Females choose their mates according to size, and the larger the whale, the deeper the mating call. Now males are free to dig in deep, instead of calling out loud.