There are many things that differentiate odontocetes or ‘toothed whales’ from mysticetes or ‘baleen whales. ’ The most obvious difference of course being that odontocetes have teeth and mysticetes have baleen. Coming in at a close second, however, is the fact that odontocetes echolocate while mysticetes do not. But, hold the boat folks: this fact may not be a fact after all. Just last year a team of scientists published an article in the Royal Society journal Biology Letters describing the first-ever recordings of something they termed “Megapclicks”: strange click sounds produced by humpback whales. The name Megapclick is derived from the scientific genus of the humpback whale Megaptera – combined with the word click.
In order to understand why this is an important discovery, let’s have a quick review of what echolocation clicks are all about . Here is what dolphin echolocation sounds like. *play clip*
The dolphin makes a click sound that it sends out in the water. When the click hits an object, it creates an echo, which then travels back toward the dolphin. By listening to the click echoes, the dolphin can then produce a kind of “mental” image of the object. Typically, a dolphin will wait to produce a click until it receives the echo from previous clicks. This means that as the dolphin moves closer to the object, it starts producing clicks more rapidly. You can hear in this audio clip how the clicks seem to speed up – in this case, the dolphin is approaching our camera. *play clip*
Okay, with that information fresh in your mind, have a listen to this clip. *play megapclicks*
This is an audio recording made from a humpback whale, and upon first listen, it sounds an awful lot like the bottlenose dolphin echolocation recording. In order to make this recording, scientists from the Hawaii Institute of Marine Biology, Woods Hole Oceanographic Institution, University of New Hampshire, and NOAA’s National Marine Sanctuary Program placed recording tags on humpback whales . The tags, known as DTAGS, are attached by suction cup to the whale’s back. The tags record the whale’s position and movements, as well as the whale’s vocalizations. The clicks recorded by the tag had two important properties: 1) they were only recorded at night, and 2) they were recorded during feeding episodes. These two observations certainly suggest that these might in fact be echolocation clicks: that is, clicks used by the whale in order to locate and track prey.
There are other clues suggesting that these clicks might be echolocation. Firstly, the click trains (or series of clicks) usually ended in a rapid series of clicks called a buzz. This pattern, called a terminal buzz, has been observed in echolocating odontocete species and usually coincides with the final phase of prey capture. These terminal buzzes were also accompanied by a sharp roll – that is, the animal turned quickly on its side – another behavior associated with prey capture.
To watch a video 3-D model reconstruction of a humpback during one if its feeding dives using Megapclicks, visit the dolphin pod website for links.
As intriguing and convincing as this all sounds, the scientists involved are very cautious about stating that humpbacks are indeed echolocating. It may be that these click sounds are simply a way for the humpback to herd or startle fish. In order for this to truly be called ‘echolocation’, we would need to know if the humpbacks are actually even able to hear these clicks themselves, let alone if they are able to use the echoes to gain object or environmental information.
At the recent Society for Marine Mammalogy biennial conference in Cape Town , scientists working on Megapclicks presented their findings. After the presentation, someone in the audience asked if the scientists had considered the idea that these click sounds might in fact be a form of communication, or more precisely, part of the humpback’s song repertoire. Humpbacks are famous for producing elaborate songs , and, according to this expert, these Megapclicks apparently resemble one of the song elements.
This discovery highlights the fact that scientists still know so very little about the behavior of whales and dolphins. Only a few decades ago, we did not even know that dolphins had a sense of echolocation; although today, we understand it to be a fundamental aspect of their behavior, biology, physiology and evolution. Whatever Megapclicks are – whether echolocation or a simple vocalization – they will be keeping scientists busy for years to come.