Natural Inquiries - Calling Dr. Bird
Bird research is teaching scientists new lessons about human health, offering promise for the treatment of ailments ranging from heart disease to sleep disorders to hearing loss
McMURDO SOUND lies under an enormous sheet of sea ice between Ross Island and the Antarctic continent. Summer comes to this area in November and lingers until February, nudging daytime temperatures into the 30s. Recently, a team of scientists from the Scripps Institution of Oceanography in San Diego, California, visited the McMurdo Station research center there to conduct experiments on emperor penguins.
These animals can dive to nearly 2,000 feet, an enormous accomplishment considering their relatively small size (adults weigh 60 to 90 pounds) and the fact that they are birds. “We’ve always thought of birds as sort of fragile canaries, yet here they are going to these incredible depths,” says Gerald Kooyman, a research biologist at Scripps.
Kooyman and his associates were interested in measuring what they presumed would be the substantial energy cost of diving deeply for prey in frigid waters. So they captured ten emperor penguins and took them out to a hole drilled in the sea ice. For two weeks, one group was kept in a corral and fed by hand while another was allowed to use the hole to catch its own fish. The scientists took blood samples from both groups to determine the energy costs of diving for prey versus resting.
When the results came back, the scientists were astonished. No substantial difference could be found in the amount of energy used by each group.
These results may sound like the arcana of a specialized scientific field, but they offer promise for the treatment of human heart disease and other illnesses. The emperor penguin is not the only bird yielding medical secrets. Swainson’s thrushes are teaching us about sleep deprivation. Zebra finches are giving us lessons in how to control our appetites. And chickens, quail and starlings are showing us how to restore hearing loss in the inner ears.
Paul Ponganis, a research physiologist at Scripps and a practicing anesthesiologist, was fascinated by the emperor penguin studies. “They have this exquisite control over heart rate and oxygen consumption,” he says. “The longer they dive, the slower the heart rate."
Emperor penguins reduce their heart rate during dives because, unlike humans, who store oxygen in their lungs, these animals store the majority of their oxygen in the outer extremities—some in blood and most in muscle. As a result, an emperor penguin’s heart does not have to pump oxygen furiously from the lungs to the extremities during the hunt. In fact, this bird may shut down the flow of blood to its limbs.
The resting heart rate for emperor penguins is about 60 to 70 beats a minute. When they dive, it may slow to 20 to 30 beats. They save most bodily functions—such as purging carbon dioxide and eliminating waste—for the surface, where the heart rate can climb to 200 beats per minute when the birds are digesting food.
But on deep dives, the supply of oxygen in the blood of an emperor penguin may get so low that scientists are baffled as to how they survive. “If that happened in our bodies, we’d have tissue damage,” Ponganis says. “There may be some biochemical secrets here that could be applicable to the treatment of stroke, shock and organ transplants in humans. In all of these conditions, there is either low or no blood flow to the organ.” Ponganis and other researchers at Scripps are continuing experiments to plumb the secrets of emperor penguins.
At Bowling Green State University in Ohio, researchers are studying Swainson’s thrushes for human-health applications. Swainson’s thrushes migrate from the coniferous forests of Canada and the northern United States to as far south as Peru and Ecuador, a distance of up to 3,000 miles that includes 12 to 14 hours of nonstop flight across the Gulf of Mexico.
During migration, these birds fly at night to avoid predators and to take advantage of the calmer atmosphere. But they do this nocturnal travel at the cost of sleep—daytime must be devoted to feeding, not snoozing. According to Verner Bingman, professor of psychology at Bowling Green, “This would have to put enormous stress on the physiology of the animals, but they don’t seem to experience negative consequences. They are a natural model of sleep deprivation.”
Bingman and doctoral student Thomas Fuchs believe that the birds rest sufficiently by taking minute-long naps during daytime periods of drowsiness. Such micro-naps have been observed in other birds, but never systematically studied until now. Only the surface has been scratched, however. For example, Bingman wonders if the thrushes also take micro-naps during flight or if, like whales and dolphins, they practice unihemispheric sleep, allowing half the brain to rest while the other half takes control.
Bingman hopes that their findings will help sleep-deprived humans such as pilots, truck drivers, business travelers and nightshift workers. “If birds display behavioral or physiological biological adaptations that enable them to compensate for sleep deprivation, maybe they can tell us ways we can minimize the negative consequences in people,” he says.
At Wright State University in Dayton, Ohio, researchers are looking at the hunger impulses of zebra finches and trying to understand how they keep their weight under control, in contrast to many of us. According to Thomas Van’t Hof, professor of biological sciences at Wright State, “Most birds don’t get fat. They gain an enormous amount of body mass before they migrate but lose it during travel and don’t get it back.”
Van’t Hof is investigating how various chemicals, chiefly melatonin, influence daily rhythms, particularly in the stomach. He is also looking at how the bird’s diet affects stomach chemistry. He thinks this research is the first step in trying to understand the chemical cues in the stomach that keep birds thin.
Researchers at the University of Washington in Seattle think birds also may harbor the secret to overcoming hearing loss in humans. Edwin Rubel, professor of hearing science, studies auditory hair cells in the inner ears of chickens, finches, quail and starlings. These cells transform sounds picked up by the outer ear into electrical impulses that the brain can read.
When humans lose their hair cells, they lose their hearing. Rubel, however, has discovered that when birds lose these cells they grow new ones. He and his colleagues are trying to discover why humans do not regenerate auditory hair cells and what processes might awaken the possibility. “If we could prevent hair cell loss or stimulate hair cell regeneration in the aging population, that would change 50 to 70 percent of the people with hearing loss,” Rubel says.
In most cases, research on the medical applications of bird biology are so cutting edge that applications have not yet been clearly defined. Nevertheless, work on birds promises clear benefits for humans. “The study of biological and behavioral processes in birds has already provided the spark for what will be wonderful advances in human health,” Rubel says, “and I expect these trends to continue to an even greater degree in the future.”
Michael Tennesen, a frequent contributor to this magazine, last wrote for National Wildlife about Humboldt squid.
Lessons from Birds
Want to Learn Something New? Just Sleep on It
Birds are often used as models for how humans learn speech. Birds learn to sing by listening to their elders and then imitating them. But Daniel Margoliash, professor in the Department of Organismal Biology and Anatomy at the University of Chicago, thinks that sleep might be an important part of the process.
In his studies, he measured the firing pattern of the nervous system when the birds sing. “The zebra finch appears to store this pattern during the day and then read it out during sleep, rehearsing the song and, perhaps, improvising variations without producing sound,” Margoliash says. He thinks the bird strengthens the pattern this way.
But does it work on humans? To find out, Margoliash and his associates conducted an experiment giving a group of humans a difficult task in vocabulary building. The researchers discovered that lessons learned in the morning were harder to recall as the day progressed. However, the following morning, after a good night’s sleep, the human subject’s recall—not unlike that of well-rested finches—was as good as immediately after the original lesson the previous day.