From the large, open-air pens where they have spent the past two weeks, eight young whooping cranes survey their surroundings. The rural, central Florida landscape of open prairie, brush, and marshlands stretches away as far as the birds can see, though only a few tens of miles separate the Kissimmee release site from the metropolitan sprawl of Orlando.
It is a humid March evening when the holding pen doors swing open for the first time. Though the cranes don't know it, this is a pivotal moment, one which marks the end of one life and the beginning of another. At first light the following morning, they will fly from the pen. For USGS biologist Dr. George Gee and other members of the Whooping Crane Recovery Program, it's nail biting time.
These birds, products of the genotype Grus americana, are also the product of modern conservation science. Each represents the culmination of years of research, lessons learned by trial and error, and untold hours of patient, meticulous care and training. As leader of the Whooping Crane Restoration Ecology Team at the USGS Patuxent Wildlife Research Center, Dr. Gee has overseen every facet of these birds' lives, from conception onward.
Now, and for the next several weeks, everything is on the line. Bobcats, over-abundant in Florida due to the decline of larger predators such as the Florida panther, have in the past taken a heavy toll on young cranes unaccustomed to life in the wild. Dr. Gee and the team know that if the birds make it through this critical post-release period, their chances of surviving to become breeding members of the Florida whooping crane population are excellent. He also knows that, in all likelihood, not all of the eight birds being released today will live that long.
"We've already lost one bird from the first group we released this year," Dr. Gee says. "I don't even count them as part of the population until they've been there at least six months. By then they've learned to avoid the bobcats."
Back from the Brink
For decades, tremendous efforts have been made to save the last wild, migratory population of whooping cranes. The recovery team includes members from Canada and the United States because these birds winter at Aransas National Wildlife Refuge in Texas, and fly north to breed in Wood Buffalo National Park in the Northwest Territories, Canada. The U.S. Fish and Wildlife Service, as the group responsible for ensuring the protection and recovery of endangered and threatened species, has been involved with the project every step of the way.
Whooping crane numbers reached an all-time low in 1941, when only 21 birds remained in the wild. Over the ensuing decades those numbers crept up only marginally. As early as the 1960s, biologists realized that simply trying to preserve the Aransas-Wood Buffalo flock was not enough. With a single population hovering around or below 40 individuals, the species was living on borrowed time. Disease could easily sweep through the wild flock, or a natural event such as a severe storm could reduce crane numbers to a point from which recovery would be impossible. (This is what happened in 1940 to a small, nonmigratory population of whooping cranes in Louisiana.) A small population size also meant that some closely related birds were breeding with each other, causing low fertility rates and developmental problems in chicks.
"To secure the species, we need to get at least two more populations established in the wild," says Dr. Gee. Specifically, goals of the recovery program, said Tom Stehn, whooping crane coordinator of the U.S. Fish and Wildlife Service, are to establish a viable, non-migratory whooping crane population in Florida, and a second migratory population that will winter in Florida and breed somewhere in the north-central United States or southern Canada. Both efforts are entirely dependent on the ability of biologists to breed whooping cranes in captivity, and raise chicks suitable for release into the wild -- an undertaking which once seemed visionary, but which has now become a reality.
In the wild, whooping cranes lay two eggs, but usually only one chick survives. Since 1967 biologists have tried to capitalize on this lost potential by harvesting one egg from nests in Canada and raising the chicks in captivity. This led initially to an increase in the number of zoo specimens, and to the establishment of a captive breeding population at Patuxent in the 1970s. However producing whooping crane chicks that could survive and breed in the wild required the advent of new physiological and behavioral conditioning techniques.
The establishment of a new migratory population is still several years off, though experiments in which young sandhill cranes have been trained to follow ultralight aircraft and trucks have been well publicized. Perhaps less well known is the fact that, since 1993, biologists with USGS, the U.S. Fish and Wildlife Service, other captive centers, and the Florida Game and Fresh Water Fish Commission have been re-introducing captive-raised whooping cranes in central Florida. The population now stands at around 73 birds, and is slowly increasing with new introductions each winter. Three pairs have established nesting territories and one female is old enough to lay. For the first time in decades, a second population of whooping cranes exists in the wild.
Building a Captive Flock
The whooping crane breeding and rearing facility at the USGS Patuxent Wildlife Research Center is the linchpin of the species recovery effort. Fifteen to twenty breeding pairs of cranes are kept at Patuxent at any one time, with occasional substitutions of individuals into or out of the breeding pool. Two other captive breeding programs are now getting under way, one at the Calgary Zoo and one at the headquarters of the International Crane Foundation in Wisconsin. Dr. Gee estimates that by 2002, the three programs will be producing about 50 cranes for release into the wild each year.
Getting these programs established, Dr. Gee says, has been a long and difficult process. One problem is that whooping cranes are slow to mature. Eight years from now, only about half of this year's female chicks will have started to lay eggs; about half the females begin to lay by eight years of age but some wait until they are teenagers. That's how long scientists have to wait to bring new birds with desirable combinations of genes into the breeding population. Conducting the necessary research also takes time. "We're constantly coming up with new things we need to know, so we keep on doing research to answer these questions," says Dr. Gee. "When we put these recovery plans together," he adds, "we're talking about decades."
One of the first challenges was to insure that the full diversity of genes remaining in the wild migratory flock was represented in the captive population. By slowly collecting eggs from all of the known Canadian nest sites, Dr. Gee and his colleagues at the Fish and Wildlife Service and on the Whooping Crane Recovery Team and other captive centers have tried to bring the entire, existing whooping crane gene pool to Patuxent.
For captive whooping cranes, all "marriages" are pre-arranged. Biologists use genetic probes to assess the degree to which chicks harvested from the wild are related, and close relatives are not allowed to breed with one another. Birds from known rare genetic lines are paired with other genetically unique individuals, to insure that at least some of this precious genetic diversity is passed on to subsequent generations.
To avoid damage or disease, fertile whooping crane eggs are kept in an incubator until they are ready to hatch. By the time the hatch date arrives, scientists have already examined a chick's pedigree and determined whether it will be eventually be slated for release or kept at the Patuxent facility. "If it's a really valuable genetic bird, we need to keep it in the captive flock," Dr. Gee says. "By the time it hatches, we're ready to condition it for whatever course it's going to take."
A School for Whooping Cranes
The central imperative of raising whooping crane chicks for release is that the young birds never see their human caregivers. In this and many other bird species, chicks which are exposed to human beings may become "imprinted" on them, and grow up preferring human companionship to that of their own kind. Thus to acquire a crane identity, chicks must be fed and cared for by cranes -- or as close an approximation as Dr. Gee and the recovery team can devise.
It begins before they are born: eggs about to hatch are played tapes of the brood calls parent cranes give to their hatching young. All feeding of chicks is done by crane-costumed scientists, using a hand puppet shaped like a crane head. After a few days, chicks are placed in small pens adjacent to live whooping crane adults, which serve as "role models" for proper imprinting.
The deception continues as the birds develop. "We don't allow anyone near the birds, unless they are in costume," Gee says. "We try to build a bird that is going to be as flighty and wild as possible." By the time the nine-month-old birds are ready for release in Florida they have still only rarely seen a human being, and these few experiences have been intentionally unpleasant. When biologists need to take a blood sample, for instance, they leave the crane suit behind.
Denied the normal process of learning by trial and error in the wild, USGS cranes are taken through a carefully designed training regimen. By the time they are a month old, birds are induced to exercise, both in water -- a heated pool -- and in runs outdoors. "We train them to follow behind us, while in costume, and we walk them for long distances," Dr. Gee says. The cranes are also given access to a small pond which has been stocked with insects, where they learn to probe for food.
Later they graduate to a larger pond, where biologists try to reinforce the whoopers' natural tendency to roost in knee-deep water. For Florida-bound birds, this aspect of their training is crucial. By selecting marshes rather than larger lakes to roost in, birds can minimize their exposure to alligators. And by standing in about 18 inches of water, the young cranes are usually far enough from dry land to be safe from bobcats.
A Gentle Release
After making the trip from the USGS Patuxent facility to Kissimmee the cranes are turned over to Florida Game and Fresh Water Fish Commission biologists, who manage the release. For two weeks, the birds are kept in outdoor pens and allowed to acclimate to their new surroundings. When the birds are released, the young cranes are watched -- carefully but discreetly -- by biologists and Earthwatch volunteers.
Dr. Gee says the recovery team believes that every release is also a research opportunity, a chance for scientists to learn something new that will help them improve the release protocol. For example, seeing what the birds do that makes them vulnerable to bobcat predation has helped the scientists make changes both in the release site and the conditioning program.
This year, a team of 11 Earthwatch volunteers is making detailed behavioral observations of cranes at the release site. Together with "personality profiles" of the birds made by USGS biologists at Patuxent, the goal is to determine whether particular behavioral characteristics give a bird a higher or lower chance of survival. This information can help scientists choose the best candidates for Florida release.
Once free, some cranes quickly depart, but others may not leave the area immediately. An automatic feeding system continues to dispense food for several weeks, but in smaller and smaller amounts, until the birds begin feeding on their own. "It's a gentle release," says Dr. Gee. "We don't force birds into the wild. They get acclimated to the environment, and to the weather. Then they're released, and they get used to finding food. And then they're gone."
As the nation's largest water, earth and biological science and civilian mapping agency, the USGS works in cooperation with more than 2000 organizations across the country to provide reliable, impartial, scientific information to resource managers, planners, and other customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, contribute to the sound conservation, economic and physical development of the nation's natural resources, and enhance the quality of life by monitoring water, biological, energy and mineral resources.
The above story is based on materials provided by United States Geological Survey, Biological Resources Division. Note: Materials may be edited for content and length.
Cite This Page: