Returning the Whooping Cranes to Florida

Editor’s Note: The story of the whooping crane is bittersweet; while it has declined in numbers in the past century, it is now giving biologists something to be happy about. And no one could tell the whooping crane’s story better than the authors, who have worked closely with whooping cranes.

If you saw the movie Fly Away Home, which tells how a father and daughter train a flock of geese to follow an ultralight plane from Canada to a winter home in North Carolina, then you have an idea of what may be in store for whooping cranes. And if you kept up with the real-life story of sandhill cranes that successfully followed an ultralight from Wisconsin to Florida last year, then you know the flight was a test of whether the same thing could be done with whooping cranes.

But the authors deal strictly with the only whooping cranes that don’t migrate -- based in central Florida. Their work is very telling about these endangered birds and how they may survive as we march into the next century. The authors’ story is about defeat, persistence, science and admiration for whooping cranes.

The whooping crane is one of the most magnificent birds in North America, and yet it is one of the rarest. A full-grown adult stands 5 feet tall and has a wingspread of 7 to 8 feet. Sexes are similar in appearance, though males are usually larger than females. Adults are mostly white with black wingtips. Legs are dark and the bill is yellowish grading to a flesh-toned pink at the base. Like all the other cranes, whooping cranes have a noticeable area on the head that serves, among other things, to signal their mood. An area of red papillose skin on the crown (bumpy, like the taste buds on your tongue) can be brightened and expanded if their mood is aggressive, or contracted and dull colored if they wish to assume a subordinate, non-aggressive posture. Further, there is a distinctive area of black whisker-like feathers on the nape and outlining the bill base.

Altogether, this is a very striking animal.

Since fall of 1980, the Florida Fish and Wildlife Conservation Commission has been involved in a large-scale project to restore the whooping crane to the southeastern United States. The Commission is the lead agency in Florida for the project; however, it involves several other agencies: the U.S. Fish and Wildlife Service, U.S. Geological Survey, the Canadian Wildlife Service, the International Crane Foundation, the Calgary Zoo and the San Antonio Zoo. The project began at the request of the Whooping Crane Recovery Team, which, as set forth in the Endangered Species Act, was charged with developing a plan to remove the whooping cranes from the Endangered Species List.

The first goal of the Florida project was to determine if and how we could reintroduce whooping cranes in the southeastern United States. They once occurred in the southeast, but by the mid-20th century were gone east of the Mississippi River. In Florida, there are reliable sight records into the 1930s. One thing we had to know before proceeding was: Could a population of non-migratory whooping cranes (as had persisted in Louisiana until the late 1940s) be established from genetically migratory stock? (The only remaining whooping cranes are migratory.) Migratory and non-migratory subspecies of sandhill cranes were used in place of whooping cranes to answer the question of whether migration in cranes is primarily acquired (learned) or innate (instinctual). Once we were satisfied that a non-migratory population of cranes could be produced from genetically migratory progenitors, we were ready to proceed.

The first release of whooping cranes in Florida involved 14 birds and occurred in February 1993. Between 19 and 48 cranes have been released each year since, for a total of 221 cranes introduced in Florida. The technique we used to release the birds was “soft release” or “gentle release.” This gave the cranes a prolonged time to get used to their new surroundings, in specially constructed release pens to allow for the gradual transition to life on their own in the wild. The majority of the birds we've released were 8 to 10 months old and were hatched and reared from eggs laid in captivity. The captive-rearing sites were at the U. S. Geological Survey's Patuxent Environmental Science Center and the International Crane Foundation.

Based on other crane release studies, we expected that initial mortality would be high, perhaps 40% to 60% in the first year. Also, we predicted predators would be the major cause of mortality. During the first 2 release years, annual mortality averaged 66%, and predation by bobcats was the source of most of the mortality.

In the 3rd year, though, we decided with the U.S. Fish and Wildlife Service and the 2 captive rearing sites to try something new. We began using smaller temporary release pens made of lightweight plastic that could be quickly erected and taken down. This allowed us to select the most suitable habitat (based on marsh and pasture conditions) for the introductions. We could respond as water levels and habitat conditions changed from year to year, or even during the release period. The goal was to introduce birds into the habitat that favored cranes, not bobcats.

A major component of this new approach was the cooperation of local private landowners. This was necessary because the best available crane habitat in central Florida was on private land. From 1995 to 2001, we released 186 cranes on 6 properties. In the first 3 years after adopting the new release method, first-year survival averaged 70%. Without the cooperation of the private landowners, this improvement in survival would not have been possible. From 1998 on, the survival rate has dropped to about 50%. We believe this is due to the impact of the ongoing drought in Florida.

There were several early project successes. The first pair formed in 1996 and made several nest platforms that year and again the next. A real milestone occurred in 1999 when 2 other pairs built nests and, for the first time in Florida, laid eggs. Unfortunately, one clutch was destroyed by a mammalian predator, and the 2nd was flooded out.

Last spring, we monitored 15 pairs of whooping cranes. Three of those pairs laid eggs, and we were able to document another major milestone: Despite severe drought conditions, a pair of whooping cranes produced the first chicks in the wild in the United States in more than 60 years! This pair of whooping cranes hatched their 2 eggs on March 16 and 18. (Crane eggs are laid and hatch at different times.)

It was fascinating to watch the changes in behavior as the parents went from incubation to brood rearing. After years of watching whooping cranes in Florida, we saw “new” behaviors that were brought out by these new parental responsibilities. The male and female, each less than 5 years of age, seemed to have no problem finding sufficient food for the chicks. For several weeks post-hatching, the parents fed the chicks small prey items, including crayfish, small frogs and aquatic insects. As the young grew, the size of prey items the parents offered grew accordingly. Snakes and aquatic salamanders became the important food items at the later stages.

We were aware from sandhill crane studies that the crane chicks go through 2 periods of heightened mortality risk before they can fly. The first period occurs between hatch and 3 weeks of age. The second is between 60 and 75 days of age, just before they are able to fly. So we monitored the rearing of these 2 milestone chicks with fingers crossed. Each day brought trepidation until we had counted both parents and their 2 orange “fuzz balls.” One of the chicks disappeared at about 10 days of age from unknown causes. The second was killed by a bobcat within a week of being able to fly.

In spite of this loss, the 2000 season was a resounding success. A pair of whooping cranes, raised in captivity and released into the wild, had demonstrated they could successfully hatch their eggs and care for the growing chicks. We now know that whooping cranes can not only survive in Florida, but will form pair bonds, and lay and hatch fertile eggs. We are confident they will successfully reproduce eventually in the wild in Florida. And in the not-too-distant future, we could have a self-sustaining population of whooping cranes in Florida. This will be one more step in assuring that this spectacular bird does not disappear forever.

WHOOPING CRANE NATURAL HISTORY FACTS

SIZE: When standing erect, whooping cranes are more than 4 feet (about 1.5 m) tall and are the tallest North American bird. Their wing spread is 7 to 8 feet (2.1 to 2.4 m).

WEIGHT: Males are 16 lbs. (7.3 kg); females are 14 lbs. (6.4 kg).

CURRENT RANGE: A natural breeding population nests in Wood Buffalo National Park in Northwest Territory, Canada, and winters at Aransas National Wildlife Refuge on the Texas Gulf coast. There’s also the experimental non-migratory flock in central Florida mentioned in this article.

HISTORIC RANGE: Whooping cranes were once found over most of North America -- from the Arctic to central Mexico and from the mid-Atlantic coast and New England to Utah, Wyoming and New Mexico. A flock of non-migratory (resident) birds was found in southwestern Louisiana until the late 1940s. The last documented nest in the United States was found May 26, 1894, south of Crystal Lake in Hancock County, Iowa.

NESTING TERRITORY: 1.3 to 47.1 cubic kilometers; average 7 cubic kilometers.

IMPORTANT HABITATS: Coastal marshes, lake shores and deep freshwater marshes with minimal disturbance by humans are used for feeding, nesting and roosting.

FOODS: Aquatic invertebrates (insects, crustaceans, mollusks), small vertebrates (fish, reptiles, amphibians, birds, mammals), roots, acorns and berries.

EGG-LAYING DATES: Late April or early May at Wood Buffalo National Park.

CLUTCH SIZE: Less than 90% of nests contain 2 eggs; others contain 1 or rarely 3; the average is 1.94 eggs.

INCUBATION PERIOD: Incubation lasts 29 to 31 days, with an average of 30 days; both sexes incubate. They will renest if the first clutch is destroyed before mid-incubation.

YOUNG: They are capable of flight when 80 to 90 days old. Chicks are cinnamon-brown; by 4 months of age, the emergence of white, adult-like feathers produces a mottled appearance. Yearlings achieve adult-looking plumage late in their second summer or fall.

BROOD SIZE: Usually 1; whooping cranes rarely succeed in raising 2 chicks.

TIME OF INDEPENDENCE FROM PARENTS: Offspring leave parents during departure from Aransas NWR for northward migration, during the northward migration or shortly after arrival on the breeding grounds.

AGE OF SEXUAL MATURITY: The first fertile eggs are produced at 4 to 7 years of age, with the average age being 5.4 years.

PAIR FORMATION: Whooping cranes mate for life but will take a new mate if the original mate dies. The pair will return to use and defend the same nesting and wintering territory year after year.

MAXIMUM LIFE: Whooping cranes live at least 22 years in the wild, perhaps to 40 years.

POPULATION: Population has gradually increased from a low of 22 in 1941 to a fall 2000 population of approximately 400: 180 in the Aransas/Wood Buffalo flock, 65 in Florida and the rest in captivity.

HISTORIC POPULATIONS: Always rare, the whooping crane population may never have exceeded 5,000 to 10,000.

REASONS FOR DECLINE AND REDEDICATION: Loss of habitat to drainage for agriculture, hunting and egg collecting reduced the population during the 19th and early 20th centuries. Wood Buffalo National Park established in 1922, but it wasn't until 1955 that it was discovered that whooping cranes nested there. Aransas National Wildlife Refuge established in 1937. Captive propagation was initiated at the Patuxent Wildlife Research Center in 1967. The first captive-produced eggs were laid in 1975.

RECOVERY GOALS: To be "down listed" from endangered to threatened status, there must be 40 nesting pairs in the Aransas/Wood Buffalo Park population and 25 nesting pairs in 2 additional, distinct locations, all reproducing at self-sustaining rates.

FLORIDA GOAL: A population of 25 breeding pairs reproducing at a self-sustain rate by 2020. That may require a population of 100 to 125 cranes, which would require the release of 200 to 250 birds.

Written By

Martin Folk is a biologist for the Florida Fish and Wildlife Conservation Commission who has specialized in whooping cranes and sandhill cranes. He has been involved with all aspects of the reintroduction of whooping cranes to central Florida for a decade.