NEWPORT BEACH, CALIFORNIA--All animals may be created equal, but some are more equal than others are. Dolphins are better communicators than previously thought, reported marine biologists at the Acoustical Society of America's meeting here last week--and manatees seem to be as dumb as their floating-sausage appearance would suggest.
For years, marine biologists have been struggling to figure out how toothed whales such as the bottlenose dolphin, Tursiops truncatus, make the clicks and squeals that they use to communicate and navigate. According to Ted Cranford, a biologist at San Diego State University, some of the bottlenose's calls are so complex that they are "more easily explained if they have two generators inside the head, operating independently."
To find out whether this is the case, Cranford and colleagues wired a bottlenose with two endoscopes--one for each nasal passage--so they could watch two sets of "phonic lips" within the animal's nasal passages as it made sounds.
Sure enough, the lips flapped independently as the dolphin squeaked and clicked. What's more, the left one flapped whenever the dolphin whistled, while the right one was silent unless the dolphin decided to give a simultaneous Bronx cheer of clicks as well.
"Before Ted's work, nobody exactly knew where sounds were produced," says Whitlow Au, a bioacoustician at the Hawaii Institute of Marine Biology in Kailua, Hawaii. Au is convinced that the dolphin does indeed use its noisemakers independently. "I think it all makes sense."
While dolphins are composing two-part harmonies, manatees appear to be stuck in a permanent communication gap, reports Renata Sousa Lima of the Laboratory of Aquatic Mammals in Brazil. She studied two species of manatee, Trichechus inunguis and Trichechus manatus, that have slightly overlapping ranges in the Amazon and different calls.
Sousa Lima and her colleague observed nine manatees in pools as the researchers piped in a variety of calls from both species through speakers. Although the manatees returned the calls and tended to swim near the speakers, the biologists found that a manatee did the same thing whether the piped-in call was from its own species or not. Thus, it seems that manatees probably aren't communicating much information with their calls--but then again, they probably don't have all that much to say.