What Bats and Whales Have in Common: Evolutionary Similarities of Echolocation

Bats and whales may not seem like they have a lot in common. One takes to the air while the other takes to the sea and one can weigh several tons while the other can weigh as little as a gram. Yet both of these mammals have something in common: the ability to use echolocation. Now, scientists have discovered that the biosonar of toothed whales and bats share surprising similarities even though they live in very different environments.

Echolocation systems are one of nature's most successful specializations. In fact, about 1,100 species of bats and roughly 80 species of toothed whales use this technique. That's about 25 percent of all living species of mammals. Yet how did such different species evolve such similar techniques? In order to find out, the researchers studied the process of convergent evolution.

In order to learn more about these echolocation systems, the researchers studied the acoustic properties in both bats and whales in the wild. This gave a much more realistic picture of how these animals use echolocation.

"Our studies have shown that the sounds of bats and toothed whales are surprisingly similar," said Annemarie Surlykke, one of the researchers, in a news release. "This is due to two things: First, all mammalian ears are developed in quite similar ways, and second--which is the most surprising--the contradicting physical conditions in air and water along with the differences in size of the animals even out the differences that you would expect in the sound frequency."

A bat is far smaller than a whale. Correspondingly, its prey is far smaller, which means that a bat needs to produce sounds with a very high frequency in order to achieve the same capacity to determine direction and size of its prey. However, the effect of the higher frequency is partially cancelled out due to the fact that the sound is transported five times as slowly and that the sound waves are five times as short in air as in water.

When these animals approach their prey, both toothed whales and bats emit a series of buzzing sounds: weak and short sound pulses at very short intervals. This complex mechanism is not fully understood by the researchers, but the animals seem to carefully control when they emit sounds and when they listen to echoes.

"The mechanism must play a key role but we do not yet know exactly which one," said Peter Teglberg, one of the researchers, in a news release. "There is a need for further studies and fortunately new technologies make it possible to track animals in the wild, study their behavior and compare these results with the knowledge we have from the laboratory."

The findings are published in the journal Physiology.