Hop, Skip, and Soar

Studying animal locomotion at Harvard's Concord Field Station

Post-doctoral fellow Gary Gillis plays "catcher" behind a tammar wallaby on a fast-moving treadmill. Hopping marsupials like kangaroos and wallabies can increase their speed without expending additional energy. "In all other mammals," says Andrew Biewener, director of the Concord Field Station, where the discovery was made, "the energy cost goes up with an increase in speed in a linear fashion." But wallabies and kangaroos store and recover the force of each hop in their elastic tendons, bouncing along by using them like a spring. The same principle allows wallaby mothers to carry loads of 15 to 20 percent of their body weight in their pouches. Says Biewener, "They carry their young around for free."
Photograph by Jim Harrison

Photographs by Jim Harrison

Goats use their horns to keep a cool head. If ever you are butted by a goat, this would make an interesting subject for ironic contemplation as you sail through the air. But it is true. A goat pumps blood into a vascular system in its horns and past the rapidly cooled lining of its nasal cavities to keep its brain at a constant 37 degrees centigrade, even when the rest of the body is considerably warmer--as it might be in a desert, for example. This little- known fact comes courtesy of Harvard's Concord Field Station, in company with a slew of others, such as the fact that bats use echolocation to track their prey. Knew that already? How about this? Rheas, which are primitive, ostrich-like birds that spend most of the day standing around grazing, have the ability to increase their metabolic rate by 3,000 percent. Nobody knows why.

Common to all these discoveries is the fact that they were made at the field station, a former Nike missile site that occupies a crown of high ground in the midst of a bosky Bedford, Massachusetts, wetland. In residence on its 62 acres are all manner of beasts: tammar wallabies, monitor lizards, emus, pigeons, ducks, magpies, cockatiels, goats, guinea fowl, toads, hyraxes, and rats. Many other species have passed through here, too, including prong-horn antelope, young lions, ostriches, reindeer, domesticated dogs and cats, chimpanzees, cheetahs, llamas, kangaroos, wolves, coyotes, Egyptian fruit bats: a regular bestiary of species representing the bipedal, flightless birds and mammals; quadrupeds; hopping bipeds; flying birds and mammals; and amphibians. All have been the subject of intense study, these days mainly into the biomechanics and energetics of how they get about in the world--the science of locomotion.

Near the main gate where visitors enter the facility, across from a goat pen, are the labs and offices of field-station director Andrew Biewener, Ph.D. '82, the Lyman professor of biology. A graduate student here in the 1970s, he was lured back three years ago, in part by the opportunity to construct a wind tunnel suitable for studying birds in flight. Up the hill from this one-story building are the underground missile bunkers, the machinery of their giant lifts for bringing payloads to the surface still in place. An enormous whale that beached itself and died a few years ago was transported here and lay on the tarmac outside as the elements--sun and rain and wind--stripped the flesh from its massive white bones. These are now stored in bunker one, with the rest of the Museum of Comparative Zoology's cetacean collection, its specimens far too large to keep in Cambridge. Vertebrae are stacked like platters on subterranean shelves, and great jawbones lean against the walls. A second bunker serves as a facility for specimen preparation, and integrates some of the curatorial functions of ornithology and entomology. Here curatorial associate Judith Chupasko, the self-proclaimed "road-kill queen," maintains a colony of flesh-eating beetles to help her clean the skeletons of animals being added to the collection. The third and final bunker, says Biewener, is being used by invertebrate geology to store "ocean floor core and sediment samples, from a Woods Hole Oceanographic Institute expedition, that provide a historical record of the earth's past history based on changes in the ocean over time."

There are discussions underway about the possibility of using the field station's ample space to build a greenhouse, but the bulk of the activity remains focused on Biewener's research group, which studies the biomechanics and energetics of animal locomotion. The late C. Richard Taylor, Ph.D. '63, Biewener's predecessor, "pioneered the comparative aspects of the field" across species and modes of ground-based locomotion, Biewener says--hence the Ark-like assemblage of former residents. His own research has focused less on the energetics--or metabolic costs of moving around--than on questions about motion's biomechanical basis. Biewener discovered that larger animals actually generate proportionately smaller forces on a mass-specific basis than small animals do--but are able to support themselves thanks to a principle called "limb mechanical advantage." Small animals' posture makes them more reliant on muscle forces to support their weight when they run. Big animals are relative weaklings, with muscles that produce less force for their weight, but by using their more extended limbs they can leverage bigger forces with every step. That explains why we don't collapse like Jell-O at the end of the day. Chalk up another discovery to the Concord Field Station.

Photographs by Jim Harrison

Lyman professor of biology Andrew Biewener directs the Concord Field Station's research into animal locomotion. The wind tunnel behind him allows study of birds in flight, while the facility's main building (top right) houses offices and lab space for the study of ground-based biomechanics and energetics. A gift to Harvard, the land was once an active U.S. Army missile site (bottom right).

Photographs by Jim Harrison

Persuading an emu to strut its stuff down a 23-meter track (above) is no easy matter, even for an experienced graduate student like Craig McGowan. Neither is catching one of these members of the ratite family (right). As their would-be captors approach, the female birds make deep thumping sounds, like drumbeats echoing in a distant cavern. With large, razor-sharp toes, and limbs that allow them to run with remarkable speed, "They can break your leg if they hit you right," says Gary Gillis. This one shredded McGowan's blue jeans, though he escaped with only a minor scratch. Once a bag has been placed over the bird's head (right, center) it calms down and remains subdued during the short trip by cart to the experimental runway. In a normal experiment, McGowan shaves the feathers from the bird's sides in order to mark its joints. Then he captures and tracks the joint and limb movements on a high-speed video camera that is synchronized with a force plate in the floor. The plate measures the ground force generated by the emu's footstrike; when combined with the video it is possible to measure the relative contribution of each joint segment to the total force created. "Emus," says McGowan, "have nice long tendons that give them good elastic energy storage." Because the birds often graze right behind the main offices, inquisitive emus appearing suddenly at the windows--like the snow-capped one above--have occasionally startled unsuspecting visitors.

Photograph by Jim Harrison

Student researcher and pre-med physics concentrator Matthew Brischetto '02 (above) is a triathlete who works with field-station research associate Peter Weyand to study the relationship between metabolic power and all-out running speed. The headgear, mouthpiece, and bag allow measurement of a running person's or animal's ability to convert oxygen into energy during both endurance and sprint exercises.

Photograph by Jim Harrison

At the wind-tunnel facility, Biewener and graduate student Tyson Hedrick (above) study cockatiels and other birds in flight. "Flying birds' movement patterns really haven't yet been described in much detail," says Biewener. "There is far less information about changes in aerodynamics and power requirements as a function of speed in flight, than there is for terrestrial-based motion." Research has shown that the work muscles do during ground-based motion is less important than an animal's ability to generate force. Measuring a walking or running animal's total performance is also difficult because many muscles are involved, across multiple joints. But in birds, "the pectoralis muscle makes up 20 to 25 percent of body weight, making it the main flight motor," says Biewener. There's a fundamental difference, too, in that "the muscles have to shorten and do work to move the wing up and down. We can learn a lot by relating that single muscle's work to the bird's total performance."

Photographs by Jim Harrison

The resident mammalian quadrupeds--goats, in this case--are not particularly cooperative either, except in the hands of animal husbandry and lab technician Pedro Ramirez (left), who can lead the herd from one pasture to another like the Pied Piper. Everyone else must do as Gary Gillis does with the goat called Twenty-One (left, right), and resort to a leash. Earlier studies at the field station under former director C. Richard Taylor focused on the comparative aspects of animal locomotion, says Biewener. Taylor began by studying the impact of size on energy cost, and the goats were part of his work tracking that cost relative to an animal's mass. "Then," says Biewener, "he went on to ask questions like, 'Is it cheaper to run on two legs than it is to run on four from an energy perspective?'" At one point, Taylor even had chimpanzees walking first bipedally and then quadrupedally--knuckle walking--to see which mode was more efficient. The answer, says Biewener, is that "basically, the energy cost is the same."
Read more articles by Jonathan Shaw

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