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Posts Tagged ‘cetaceans’

Cross-Species Gadget Tests Reveal Reason for Dolphin Tools

25 Jul

The dolphins of Australia’s Shark Bay, famed as Earth’s first marine tool-users, likely turned to gadgetry because echolocation couldn’t find the best fish, especially for hurried moms without time to hunt.

It was in 1984 that researchers first observed the dolphins fitting basket sponges over their beaks, then scraping through seafloor mud to disturb hidden fish. Research subsequently showed this behavior to be full-blown tool use, taught by mothers to their daughters and representing a profound difference in lifestyle between them and Shark Bay’s other bottlenoses.

A basic question remained unanswered, however: Though sponges clearly protected sensitive dolphin snouts from jagged pieces of rock and coral, why scrape seafloor at all? Why not rely on echolocation to pinpoint target prey?

In a study published July 20 in Public Library of Science ONE, biologists Eric Patterson and Janet Mann of Georgetown University set out to answer this question by mounting basket sponges on sticks and pushing them through Shark Bay seafloors, just as dolphins do.

Most fish scared from the muck were bottom-dwellers lacking swim bladders, the air-filled organs that help fish control their buoyancy. Compared to fish flesh, which interferes with acoustic signals just slightly more than water, air bladders stand out on sonar. Without them, bottom-dwelling fish are nearly invisible to echolocation. Hence the value of scraping through seafloors manually, and thus the need for a device that protects dolphin noses from scraping.

Hunting with sponges has allowed Shark Bay’s bottlenoses to fill an empty ecological niche, eating fish that other dolphins ignore, wrote Patterson and Mann. The findings also suggest why sponge foraging likely arose among Shark Bay’s females and has remained their province, taught by dolphin mothers to daughters rather than sons.

Whereas dolphin fathers are mostly absent, free to roam and chase prey in the open ocean, dolphin moms spend years with their calves. They need to put food on the figurative table but have little time to do it. Sponge foraging is convenient and nutritious, a family recipe for quick-but-delicious dinners passed on to daughters who will someday need it.

Image: Eric Patterson/PLoS ONE

See Also:

Citation: “The Ecological Conditions That Favor Tool Use and Innovation in Wild Bottlenose Dolphins (Tursiops sp.). By Eric Patterson & Janet Mann. PLoS ONE, July 20, 2011.

 
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Sperm Whales May Have Names

14 Mar

Subtle variations in sperm-whale calls suggest that individuals announce themselves with discrete personal identifier. To put it another way, they might have names.

The findings are preliminary, based on observations of just three whales, so talk of names is still speculation. But “it’s very suggestive,” said biologist Luke Rendell of Scotland’s University of St. Andrews. “They seem to make that coda in a way that’s individually distinctive.”

Rendell and his collaborators, including biologists Hal Whitehead, Shane Gero and Tyler Schulz, have for years studied the click sequences, or codas, used by sperm whales to communicate across miles of deep ocean. In a study published last June in Marine Mammal Sciences, they described a sound-analysis technique that linked recorded codas to individual members of a whale family living in the Caribbean.

In that study, they focused on a coda made only by Caribbean sperm whales. It appears to signify group membership. In the latest study, published Feb. 10 in Animal Behavior, they analyzed a coda made by sperm whales around the world. Called 5R, it’s composed of five consecutive clicks, and superficially appears to be identical in each whale. Analyzed closely, however, variations in click timing emerge. Each of the researchers’ whales had its own personal 5R riff.

‘This is just the first glimpse of what might be going on.’

The differences were significant. The sonic variations that were used to distinguish between individuals in the earlier study depended on a listener’s physical relationship to the caller: “If you record the animal from the side, you get a different structure than dead ahead or behind,” said Rendell. But these 5R variations held true regardless of listener position.

“In terms of information transfer, the timing of the clicks is much less susceptible” to interference, said Rendell. “There is no doubt in my mind that the animals can tell the difference between the timing of individuals.” Moreover, 5R tends to be made at the beginning of each coda string as if, like old-time telegraph operators clicking out a call sign, they were identifying themselves. Said Rendell, “It may function to let the animals know which individual is vocalizing.”

Audio: From a 2008 study of overlapping codas in pairs of sperm whales. One animal produces 1+1+3, the apparent group-level identifier. Both then produce overlapping 4R codas. After that, the first whale continues with 4R, while the other switches to 1+1+3. Finally, both make 1+1+3. The full meaning of such exchanges remains unclear, but they appear to reinforce social bonding.

Rendell stressed that much more research is needed to be sure of 5R’s function. “We could have just observed a freak occurrence,” he said. Future research will involve more recordings. “This is just the first glimpse of what might be going on.”

That individual whales would have means of identifying themselves does, however, make sense. Dolphins have already been shown to have individual, identifying whistles. Like them, sperm whales are highly social animals who maintain complex relationships over long distances, coordinating hunts and cooperating to raise one another’s calves.

Sperm-whale coda repertoires can contain dozens of different calls, which vary in use among families and regions, as do patterns of behavior. At a neurological level, their brains display many of the features associated in humans with sophisticated cognition. Many researchers think that sperm whales and other cetacean species should be considered “non-human persons,” comparable at least to chimpanzees and other great apes.

Compared to primates, however, studying the behaviors and relationships of whales is extremely difficult. They don’t take well to aquariums, and observations in the wild take place on their aquatic terms.

What’s been observed so far are just “the crude behavioral measures we get by following them in a boat,” said Rendell. “I’d argue that there is probably a vast amount of complexity out there in sperm whale society that we have yet to understand. As we get to know more about them, we’re going to continue to reveal complexities that we didn’t anticipate.”

Image: NOAA. Audio: Luke Rendell.

See Also:

Citation: “Individually distinctive acoustic features in sperm whale codas.” By Ricardo Antunes, Tyler Schulz, Shane Gero, Hal Whitehead, Jonathan Gordon, Luke Rendell. Animal Behavior, Feb. 10, 2011.

 
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