October 8, 1997
Contact: Robert Irion, (408) 459-2495, [email protected]
UC SANTA CRUZ SCIENTISTS UNVEIL THE SENSORY AND COGNITIVE WORLDS OF PINNIPEDS
No other research group has learned so much about how seals and sea lions process information
FOR IMMEDIATE RELEASE
SANTA CRUZ, CA--A remarkable quartet of trained marine mammals is helping scientists push the frontiers of animal psychobiology by demonstrating, in unprecedented detail, how they see, hear, and think about the world around them.
Years of careful experiments at the University of California, Santa Cruz, have painted a fascinating picture of the sensory and cognitive experiences of pinnipeds--the four-flippered, amphibious carnivores that include elephant seals, sea lions, and harbor seals. Their awareness of the world, it seems, has evolved to meet both the general needs of marine mammals and the special challenges each species faces in day-to-day life.
The research is revealing how human impacts might hinder a pinniped's abilities to identify family or foe, communicate, navigate, and solve other problems. The work also illuminates the roots of language development: At least one of the animals can form complex nonverbal relationships among objects, an ability that some researchers had ascribed only to humans.
"Animal behavior is intriguing because they don't have language--they don't code the world around them in symbols, as humans do," said Ronald Schusterman, adjunct professor of biology and ocean sciences at UC Santa Cruz. "Yet they do so many intricate things, both socially and in terms of foraging, navigating, and avoiding predators like great white sharks and pods of killer whales. These behaviors are very versatile and flexible. Our animals aren't thinking verbally, but we know that they're thinking."
Schusterman's team, based at UCSC's Joseph M. Long Marine Laboratory on the shores of Monterey Bay, has earned a reputation as one of the best in the world for studying the intelligence of marine mammals. In recent years, the researchers have extended their focus beyond animal cognition to encompass the broader issue of how their subjects gather and process information--in essence, mapping the "perceptual world" of a pinniped.
"We take an integrated and systematic approach to studying problem solving in our animals," said marine biologist Colleen Reichmuth, who received her master's degree under Schusterman. "It's difficult to do that if you don't understand what kind of sensory information the animal takes in from its environment."
All of the blubbery and engaging actors in this scientific play were born in captivity or rescued as stranded orphans. Their training and research sessions are voluntary, refined to precise protocols during Schusterman's four decades in animal experimental psychology.
Two of the animals are female California sea lions (Zalophus californianus). Rocky, the eldest at age 21, mastered a sign language under Schusterman in the 1980s. Her cautious approach to new experiences reflects her one year in the wild as a pup. Rio, hand- raised at the lab and now age 12, is like an eager and demanding child. By all appearances she loves her role as a scientific pioneer, splashing excitedly from task to task and excelling at all of them.
Sprouts, a nine-year-old male Pacific harbor seal (Phoca vitulina richardsii), is laid back compared to his raucous neighbors but has yielded important insights in the vision and hearing projects. Four-year-old Burnyce, the world's only trained northern elephant seal (Mirounga angustirostris), can be stubborn and sluggish. But she's caught on surprisingly well and has offered glimpses of the amazing evolutionary adaptations of these deep-diving animals.
"All of them are fun to work with and wonderful to train," said Schusterman. "There's a lot of similarities between them and us. They have emotions and motivations, just as we do, and many of the same basic needs. The ways in which we and they react to the world are not all that different."
Following are brief overviews of research highlights from each of the three project areas.
----- Cognition: Precursors to language? -----
An apparatus that looks similar to the child's game "Concentration" has garnered the group much attention over the years.
Schusterman's coworkers train Rocky and Rio to match pairs of pictures, exposed within small windows in a poolside wooden frame. For each correct pairing (identified by the sea lion with a touch of its nose), the animal gets a fish. We see each symbol as a letter, or a flower, or a teapot--but to the sea lions, they're just random shapes.
Once the animals learn many pairings, the researchers examine what choices they make when given new combinations. If "A" goes with "B," for instance, and "B" goes with "C," would the sea lions deduce instantly that "C" goes with "A"? About five years ago, the team demonstrated that at least one animal--Rio--could do this, and do it easily.
Many researchers had believed that spoken language was a prerequisite for this ability, called "equivalence." Instead, some animals may possess cognitive skills that linguists would regard as forerunners of language, even though the animals obviously are nonverbal.
More recent work, led by Reichmuth, has strengthened this conclusion by showing that Rio also can form "functional classes," another complex task. Rio learned to sort shapes, in this case letters and numbers, into different categories. After she mastered this skill, Rio immediately could relate the members within each class to one another. She also could expand the classes to include new letters and numbers.
These skills, the researchers claim, cannot stem simply from instinct or trial and error. Rather, it appears that more complicated thought processes are innate--at least to Rio, and perhaps to other members of her species as well.
Why should a sea lion have these abilities when it can't say out loud what it's thinking? It all boils down to problem solving in the environment, Schusterman believes. To survive, a lone pup among thousands on a beach must recognize its mother across the different senses of sight, smell, and sound--and vice versa. Adults must classify their kin, recognize which predators to avoid, and navigate in three dimensions. The skills they've found in Rio, the group maintains, could form the basis of a cognitive mechanism that sea lions use to cope in the wild.
"You'd be hard pressed to think of any problem in your life that doesn't require you to use language to solve it," said marine biologist David Kastak, who earned his Ph.D. in Schusterman's group. "Other animals are solving similar complex problems, but without language."
----- Hearing: The din of the ocean -----
Pinnipeds may not talk, but they growl, bellow, snort, whine, and caterwaul with abandon. All of this helps make the ocean and onshore breeding grounds very noisy places indeed. Add the cacophony of civilization and industry, and one might wonder how marine mammals hear what they need to hear.
Schusterman's group wondered that, too. So, led by Kastak, the team undertook a methodical effort to gauge the hearing abilities of its four charges, both in air and in water. They devised an experimental setup that is analogous to the classic hearing test for humans: Wear headphones, raise your hand when you hear a tone. A child might get a lollipop for performing well on this test, but Burnyce and her gang get fish.
For the aerial tests, the group directs tones into the animals' ears via headphones held on by nylon straps. Under water, sounds emanate from a speaker. Each subject is trained to touch a ball with its nose if it hears--or thinks it hears--a sound. "False alarms," when the animal touches the ball even though no sound was played, help the researchers spot overeager cheating.
The team tested each animal at different frequencies of sound, from low- to high-pitched, to create baseline "audiograms." The results, compared across species, were remarkably reflective of the animals' evolutionary histories:
-- The California sea lions hear well in air but are less sensitive in water. Many important social interactions for this species occur on land, Kastak explained. Most critical are the mutual and unique acoustic identifications between mothers and pups.
-- Sprouts, the harbor seal, hears equally well in air and in water. Of the three species the harbor seal is most truly amphibious, giving birth on land but breeding and socializing extensively in water. Unlike sea lion pups, young harbor seals swim soon after birth.
-- Burnyce hears far better in water. That's no shock, as elephant seals spend an extraordinary amount of time in water up to a mile deep. Their ear canals are very narrow, probably to prevent pressure-induced problems at great depths. This may explain why elephant seal rookeries can get so deafening, Kastak said--they're all basically hard of hearing in air.
The group was surprised to find that Burnyce hears fairly well at high frequencies. Many researchers had assumed that elephant seals were low-frequency specialists, based on the anatomies of their ears. Detecting high frequencies may help them avoid a key predator, the killer whale, which echolocates with high-pitched clicks.
In ongoing work, the team is finding that exposure to loud sounds can induce "temporary threshold shifts," or slight but transient hearing losses, in their animals. Just as our ears feel cottony after a rock concert, it appears that marine mammals lose some sensitivity if they venture near a tanker or a seismic survey explosion. For a short time, they might not hear the grunting erotica of a potential mate or the plaintive "Mom?" of a pup.
Schusterman first measured evidence of this effect in Sprouts when workers cleaned a nearby tank at Long Marine Lab with a sand blaster. Now, under controlled conditions, the researchers are showing that even moderate sounds can induce threshold shifts for a few hours. For ethical reasons, the team will not study permanent hearing loss, although it probably does occur in the ocean.
"Manmade noise, especially shipping traffic, is far more of a pollutant than anything else humans have put into the water," said Kastak. "It's not innocuous. If we can quantify the impacts of these sounds on our animals, we might be able to make predictions about the environmental effects."
Other current research, coordinated by graduate student Brandon Southall, is probing the "masking" effects of continuous sounds in our increasingly noisy seas. A persistent sound, even if not loud enough to have a physiological impact, might prevent marine mammals from hearing what they need to hear at a given moment. Then again, they may have evolved the ability to pick out key signals, just as we can isolate one conversation from a cocktail-party buzz.
----- Vision: To the depths, darkly -----
Do pinnipeds *hear* their prey, or do they *see* them? Schusterman's hypothesis is that it's both, but primarily the latter: Those big watery eyes just soak up photons, even at great depths.
If that's the case, then deeper diving animals should have more sensitive eyesight, since they need to forage at lower levels of light. Graduate student David Levenson has explored that notion over the past few years with a pair of innovative experiments on Rio, Sprouts, and Burnyce. (Rocky, who has age-related cataracts, sat this one out.)
First, Levenson trained the animals to remain still in a darkened room while facing a device that let him control, with precision, the amount of light shining into their eyes. With an infrared camera, he measured the dilation of their pupils at different brightnesses, ranging from ambient light to near darkness.
Burnyce, whose species routinely plummets from the bright ocean's surface to the shadowy depths below, proved the most dark- adaptable of the three. Indeed, her pupils were still constricted--a sign of greater sensitivity--at a light intensity about 100,000 times dimmer than the levels at which Rio's and Sprouts' pupils had become fully dilated. "No one expected that," Levenson said. "It's an unbelievably huge difference."
In the second set of experiments, Levenson zeroed in on the faintest flashes of light that the animals could *perceive*--a more robust indicator of their visual capacities. He built a light-tight enclosure over a small pool, in which each subject floated while watching for the light. Just as in the hearing tests, a correct response (touching nose to ball when the light flashed) netted a fish. Levenson monitored the animals' actions via a small infrared camera and adjusted the intensity of the flashing light from above the pool with a clever system of filters.
Again, Burnyce detected flashes at far lower levels than her companions. Rio was slightly better than Sprouts, a sensible result because California sea lions forage almost exclusively at night. However, with just one experimental subject for each species, the team can't draw too many broad-based conclusions about their kin in the wild.
"We pretty much understand what pinnipeds do on land, but many of their behaviors in the ocean are a black box," Levenson said. "This provides us with some baseline biological evidence of how their aquatic visual systems might work." Scientists have not yet ruled out that pinnipeds also might echolocate on occasion or use other nonvisual means to listen or feel for prey, Levenson said. However, his results show that for many species, vision probably is the most important sense.
A better grasp of the visual abilities and limitations of various pinnipeds, Schusterman noted, could help inform conservation management plans. Oil spills, nearshore pollution, or sedimentation that increases the opacity of water might cut the animals' odds of finding a meal.
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Editor's notes: Reporters and photographers are welcome to visit the Schusterman research group by appointment only. Only a limited amount of time each week will be open for interviews and filming. For an appointment, contact Robert Irion at [email protected] or (408) 459-2495.
A set of five color slides illustrating the research is available.
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