Whales Sing for Sex and Food

The blue whale is the largest animal that ever existed: it reaches over 33m (100 feet) in length and over 180 tonnes.

So, it's understandable it was one of the main targets of the whale hunters, being extremely endangered before whaling moratoria were enacted.

In two recent studies on blue whales, researchers at Scripps Institution of Oceanography at UC San Diego used a combination of techniques to understand what's the whales' singing and how the songs can be used for sex identification and population number estimations. Songs were supposed to mediate social interactions, but their precise role was unknown.

The first investigation detected the behavioral context of songs, using an eastern North Pacific blue whale population. "This is the first study that has been able to study the calls by directly observing the animal while it is calling and gathering key information such as depth and body orientation-getting a sense of what the animal is doing underwater," said postdoctoral researcher Erin Oleson. "Once you understand the context of specific types of sounds, then you can use those sounds to infer something about what they are doing when you are not there to actually see them doing it."

The team attached, via suction cups, miniature acoustic recording tags and integrated video-camcorders to whales, in order to connect whale song types to behavior, sex and group size.

This information was completed with tissue analysis and visual observations. The study discovered that only males produced the "AB" calls while "D" calls were emitted by both sexes, while foraging. These observations point that AB songs must have a role in reproduction.

Understanding the meaning of the whales' song is important in assessing their habitats and abundance. The second approach tried to assess worldwide blue whale populations by investigating differences in the songs of different populations.

The researchers analyzed acoustic recordings from around the world to make a new map that geographically categorizes blue whale types into nine regions around the world based on their song "dialects."

The stock structures of blue whales should be evaluated based on their song, which depicts more accurately their true population distributions. "By listening to the animals, you can tell something about the areas in which they are interacting to breed and that's important to know for managing and conserving the animals," said scientist John Hildebrand.

Photo: Blue whale feeding