Tuning In To Humpback Whales
Not only do these marine leviathans have musical fads, but females wander while males go cruising for bruisings
THE KOHOLA II was only 30 minutes out of the harbor on Maui when researchers aboard spotted a group of humpback whales boiling at the distant surface. Adam Pack, assistant director of the Kewalo Basin Marine Mammal Laboratory of the University of Hawaii, directed the boat's crew to head toward the churning animals.
Soon the vessel sat near a group of about ten males circling around a female. The males were competing for the prized position of principal escort--the one that would swim nearest to her and presumably have first mating rights. The males butted each other with their heads and slashed out with their flukes in a struggle for supremacy. Pack, dressed in a wet suit and carrying an underwater video camera, slipped over the side and into the water to capture the spectacle on tape.
Pack and other researchers around the globe are trying to uncover the secrets of humpback whales. Though the humpback is one of the most studied of the great whales, riddles about its mating and social behavior remain unsolved. While Pack and his colleagues are studying reproduction off Maui, scientists off southeast Alaska and in the Gulf of Maine are looking at cooperative feeding. And still others in Australia are listening to humpback songs and the startling influence of a few wandering humpback minstrels, remarkable evidence of what may be the whale's own unique form of culture.
As strange as it may sound, humpbacks and other whales actually evolved from a terrestrial ancestor that also gave rise to sheep and deer. Nearly 100 million years ago, a population of these mammals moved back into the sea, and during thousands of generations adapted to aquatic life. Their nostrils, for example, slowly moved up to the top of their heads.
Humpbacks differ from their relatives primarily by their long flippers, which can stretch 15 feet or more. The creatures also have stepped or humped dorsal fins, from which they received their name. Like other baleen whales, humpbacks feed mostly on krill and small fish. They favor shallow banks and near-shore waters and can be gregarious--behaviors that made them easy prey for whalers in the nineteenth and early twentieth centuries. From estimated pre-whaling numbers of 150,000 or more, humpbacks were hunted nearly to extinction. Listed as endangered since 1970, the worldwide population is as many as 20,000 today.
Though endangered, humpbacks are still found in every ocean. They spend summers feeding in cold, high-latitude waters, and move to warmer climates to reproduce each winter. About 4,000 humpbacks, the largest population in the North Pacific, migrate to Hawaii each year from their summer feeding grounds in Alaska and elsewhere in the North Pacific Rim. These whales are a major tourist draw today, but 25 years ago they were largely unknown. "There were rumors but few people had actually reported seeing them in the islands," says Lou Herman, director of the Kewalo Basin lab.
Photo: © FLIP NICKLIN (MINDEN PICTURES)
MIGRATION MYSTERY: In Hawaii, the southern end of their Pacific migratory journey, humpbacks fast. Scientists aren't sure why the whales swim 3,000 miles south each year; possibly the warm water makes life easier for calves such as this one, swimming with its mother. Adult males also court and compete for mates in Hawaii, which may be the impetus for the humpback songs recorded by researchers.
In 1975, Herman began research on the humpback--now the longest continual study of these whales in Hawaii. One of the things that he and his associates discovered was that humpbacks are not the gentle giants many had thought. Competition between males on the reproductive grounds is a dangerous game.
Pack and Herman's video work off Maui documents that competition and reveals the roles that individual whales play. After a typical day with the whales last year, Kewalo Basin researchers sit in their headquarters on Maui and play back the videotape. On the screen is a large female, a calf at her side, with fighting males circling around her. Also on-screen is Pack, a video camera in one hand and a sonar device that looks like a flashlight in the other. He videotapes the whale and activates the sonar, and then tapes the display on the sonar. This tells him how far he is from the whale.
Mark Deakos, a graduate student with the lab, takes the tape and puts it in a playback machine attached to a computer. When a large male comes into view on the tape, he captures the whale's image as a single frame and measures it on the computer screen. Then he puts this statistic and the distance to the animal into a computer program that calculates the real length of the animal. Knowing the size of the whale, the biologists can determine whether it is an adult (adult males average 44 feet in length) or if it is sexually immature (juveniles average 38 feet). "Past the age of about one and a half to two years, it's very difficult to determine by eye the sizes and thus the ages of humpback whales," says Pack.
Kewalo Basin scientists are finding that the largest males in these groups have a competitive advantage over other males, and that these larger males prefer the largest females. They have also learned that 44 percent of the males in competitive groups are juveniles that seem to be simply watching. Since they'll lose about half their body weight fasting during the winter, they are essentially traveling thousands of miles to attend a very expensive school on mating behavior.
These juveniles are learning what a whale has to do to become a principal escort. The privilege of this job, scientists believe, is the right to mate first with the female when she becomes receptive. But this privilege must be earned by fighting off would-be escorts. If another male tries to cut in, the principal escort must draw on his arsenal of defensive tactics. The first step may be to throw a block by hurling himself between the female and the challenger. If that doesn't work, he may inflate his throat pleats to make himself appear larger. He may also release a trail of bubbles from his blowhole or mouth to disorient the competition.
If none of that works, he's got to get tough--butting his challenger with his chin or striking out with his flukes. The Kewalo Basin scientists often see whales during the mating season that have bloodied heads and fins from these encounters. Occasionally, they see worse. One day in 1996, the researchers got an emergency call from a whale-watch boat. The boaters were viewing a competitive group when, suddenly, there was a whale lying at the surface with other whales around it. "They thought maybe this was a mating episode or a female about to give birth," says Pack. "But when we got there we realized the animal--a male--was dead. When these competitive groups get going, the violence can really escalate."
Though Hawaii is believed to be a major reproductive ground for the whales, no one has ever seen humpback whales mate. Some researchers believe mating may happen at night or in deep water. Others say much of it may not happen in Hawaiian waters at all, but along their migration route.
The belief that humpbacks may mate somewhere else arose from studies of photos of the whales. When humpback whales surface, they take a few breaths and then dive, often exposing their tail flukes in the process. Photographs of the unique color patterns and serrations of the whales' tails allow researchers to identify individual animals. Alison Craig, a researcher at Kewalo Basin, analyzed a collection of 13,000 tail fluke photos for her doctoral thesis. She found that there were about two males for every female off Maui. When she compared this with the photos taken off Alaska in the summer, she learned that the ratio of males to females was about even. Where did the rest of the females go during winter?
Scott Spitz, another Kewalo Basin researcher working on his doctorate, used videotapes to tackle the issue of when humpbacks mate. By measuring calves at different times during the winter season, he was able to calculate the estimated time of birth. Then he subtracted 11.5 months, the period of pregnancy for a whale, to determine the time of conception. "What we found was that most of the calves were conceived two months before most of the whales arrived in Hawaii," says Spitz.
Craig now believes she knows where the females go. "Once a female becomes pregnant it's no longer necessary to continue on to Hawaii," she says. "The best thing she can do is to get back up to the feeding grounds off Alaska so she can maximize her food intake."
The female heads back to the dinner table because the following year when she returns to Hawaii she will have a hungry juvenile in tow and will need to produce vast quantities of milk. And she must perform this task while fasting, losing half her body fat while her calf more than doubles its weight.
Biologists still aren't sure why humpbacks and other baleen whales make the long, costly journeys to lower latitudes each winter. One theory is that the waters off Hawaii are warmer and calves don't need as thick a layer of blubber at birth. Another is that these waters have fewer predators, particularly killer whales, which are more frequently found in colder waters. John Calambokidis, with Cascadia Research in Olympia, Washington, studied humpbacks off the Pacific coast and found that more than 25 percent had teeth marks on their bodies from killer whale attacks.
Calambokidis has tracked different humpback whale populations to get an idea of the distances they go on these migrations. The round-trip from Alaska to the Hawaiian Islands is about 6,000 miles, but one whale off Colombia traveled all the way to Antarctica, a round-trip of 10,300 miles. And these aren't slow boats to China, either. One tagged whale swam from Hawaii to Alaska in 39 days.
Some of the whales' behavior is markedly different on each end of these long journeys. Humpbacks that fought pitched battles on wintering grounds may become close allies on feeding grounds. Researchers at the Alaska-British Columbia Whale Foundation have witnessed groups of humpbacks diving below fish schools or krill swarms and blowing what becomes a large bubble net around their prey. Then the whales rocket up through the center of these bubble nets to devour the fish or krill. Scientists point out that not only is this behavior cooperative, but it actually qualifies as a form of tool use.
In the Gulf of Maine, humpback whales augment this technique by slapping the surface of the water with their tails, stunning their prey before diving under the surface. Biologists first observed this behavior, dubbed "lobtail feeding," in 1981, and by 1989 nearly 50 percent of the population had adopted it. Researchers at the Whale Center of New England spotted a number of calves that lobtailed, though their mothers did not. "The calves are learning it from other members of the population," says Kate Sardi, assistant director of the Whale Center. "We believe this is very definitely a cultural transmission of that behavior."
The notion of humpback culture got another big boost from scientists listening to humpback songs in the waters off Australia in the late 1990s. The researchers heard 2 males singing a different song from the other 80 singers recorded off the east coast of Australia in 1995 and 1996. In 1997 the song began to gain popularity, and by 1998 the researchers heard only the new song. Biologists at the Australian Marine Mammal Research Center argued that this was pop culture, fickle and faddish. A couple of whales had set a musical trend, much like the Beatles or the Spice Girls.
Photo: © FLIP NICKLIN (MINDEN PICTURES)
SOULFUL LOOK? This male is one of many vocalists active in Hawaiian waters. Scientists have found that humpback tunes come and go, offering evidence of a fadlike whale culture. The exact function of humpback song is still unknown. Since vocalists are often smaller and less successful in courting than their brethren, maybe they are singing the blues.
Why the fuss over the latest whale tunes? Since most whale singing occurs during the breeding season, many scientists believe it plays a role in breeding behavior. "It is like bird song in that it is a reproductive advertising display used by males to indicate a readiness to mate with a female and also to compete with other males," says Peter Tyack, a senior scientist at Woods Hole Oceanographic Institution.
But others argue that there is more to it than that. Engineers at the University of Massachusetts-Dartmouth recently analyzed humpback whale songs and found that they appear to have complex syntax--an overall organizing structure, one of the key components of language. But Tyack thinks it may be an error to look for language in humpback songs. There is little evidence that changes in humpback songs reflect changes in their messages, Tyack says. "I think it's much more about style," he says. "This is not a few males saying, ‘My food over here is better than yours.' It's probably that the females like the aesthetic style of the new whale music and the other males have to follow suit."
Does whale song really get the females? Kewalo Basin data show that the principal escorts in the competitive groups tend to be the biggest males and that the singers are smaller, on average. Perhaps the smaller males are singing the blues because they can't succeed in competitive groups.
Tyack thinks there may be two mating strategies for males. One strategy is to attract females by singing; the other is to compete within a group for access to a female. Individual males can switch strategies in the same day, and many appear to take up singing after dark when physical competition is less appropriate. Recent studies reveal that the general level of sound in the waters off Hawaii ramps up after the sun goes down.
It's not necessary to wait until dark to hear the humpbacks singing in Hawaii, however. After their morning of videotaping whales off Maui, for example, the crew of the Kohola II stops for lunch and the researchers go swimming. Suddenly the water is alive with the song of a nearby but unseen humpback. Pack and his colleagues dunk their heads excitedly into the water to hear the tune--a loud, long, slow lament.
The scientists don't yet fully understand the meaning of this song, nor several other aspects of humpback whale behavior. But the Hawaiian researchers and other experts around the world continue to listen intently.
Writer Michael Tennesen traveled to Hawaii to accompany Kewalo Basin lab scientists as they studied humback whales. For more information about the lab's research program, and how you can participate in it, see