Whooping crane population reaches record high.
A record 237 endangered whooping cranes (Grus americana) arrived in their Texas wintering grounds in 2006-2007. This is likely the highest number of whoopers wintering in Texas in the past 100 years, and it exceeds last winter's record by 17. There is definitely cause to celebrate; the wild population has doubled over the past 20 years.
The increase was due to excellent nesting production in 2006. The Canadian Wildlife Service reported that 62 nesting pairs fledged a record 49 chicks on their nesting grounds in Wood Buffalo National Park, Canada. The 45 surviving chicks that arrived in Texas set another recovery record. Seven sets of adult pairs even arrived with two chicks each. This is yet one more record; whooping cranes normally hatch two chicks, but usually only one survives.
Flock updates one year ago had not been as optimistic, with the peak population size determined at 220 for the 2005-2006 winter, only a slight increase. Production was once again very good in Canada, with 30 juveniles making it to Aransas in fall 2005, but higher than average mortality of about 25 birds (11.6 percent of the population) between the spring and fall of 2005 allowed the flock to grow by only a few individuals. Much of the mortality of fledged whooping cranes comes from collisions with power lines during migration stopovers. Shootings, one of the major causes of the historic decline of whooping cranes along with habitat loss, now occur infrequently. The last known shooting of two whooping cranes occurred in Kansas in early November 2004. One died within a week, and the second later died from respiratory problems that developed from its injuries. Veterinarians at Kansas State University had surgically repaired the wing of this crane, with hopes that it could survive to contribute to the captive breeding flock. The Kansas Department of Wildlife and Parks flew the whooper to the USGS Patuxent Wildlife Research Center in Maryland, but the bird died after arrival. Charges filed against a party of sandhill crane (Grus canadensis) hunters involved in the shooting resulted in a guilty plea with fines of $3,000 per hunter, additional restitution paying the medical bills incurred caring for the injured cranes, community service, and loss of hunting privileges for two years.
Whooping cranes are the tallest birds in North America, standing nearly five feet (1.5 meters) tall with a wingspan wider than most cars. The only remaining natural population nests in Wood Buffalo National Park on the border of Alberta and the Northwest Territories in Canada and migrates 2,400 miles (3,860 kilometers) through the prairie states and provinces to the Texas coast. During the 2006 fall migration, however, five whooping cranes were confirmed at Grulla National Wildlife Refuge in New Mexico. (Grulla, appropriately, is the Spanish word for crane.) This sighting adjacent to the border of west Texas was the second confirmed sighting of Aransas-Wood Buffalo population (AWBP) whooping cranes in New Mexico.
Whoopers winter on the Texas Coast on and near the Aransas and Matagorda Island national wildlife refuges about 45 miles (72 kin) north of Corpus Christi, Texas. Both their summer and winter range is restricted to a 25-mile (40-km) radius. Whooping cranes use a variety of habitats, including coastal and inland marshes, lakes, ponds, wet meadows, rivers, and agricultural fields. Wintering whooping cranes forage primarily for blue crabs in salt marsh habitat, while in summer they hunt fresh water ponds for minnows, a favorite food. Habitat at Aransas was good in the 2006-2007 winter due to high rainfall on the coast and adequate freshwater inflows into the bays. Inflows boost the blue crab population and lower marsh salinities, allowing cranes to drink directly from the marsh. Unlike most bird species, whooping cranes are territorial in both summer and winter and will defend and chase all other whooping cranes out of their estimated 350-acre (140-hectare) territories.
Historic population declines resulted from habitat destruction, shooting, and displacement by human activities. The species reached a low of only 21 birds in 1941. It has been listed as endangered in the United States and Canada since the 1970s. Current threats include limited genetic diversity, loss and degradation of migration stopover habitat, collisions with power lines, degradation of coastal habitat, chemical spills, and sea level rise.
Although the whooping crane population remains endangered, the population has been growing at more than four percent annually and first reached 100 birds in 1986 and 200 birds in 2004. Whoopers currently exist in the wild at three locations and in captivity at nine sites. The February 2007 total wild population is estimated at 353. This includes 237 individuals in the only self-sustaining population (Aransas-Wood Buffalo), 53 captive-raised individuals released in an effort to establish a non-migratory population in central Florida, and 63 introduced individuals in the eastern U.S. that migrate between Wisconsin and Florida. The current total breeding captive population at the Calgary Zoo, International Crane Foundation, Patuxent Wildlife Research Center, the Species Survival Center in New Orleans, and the San Antonio Zoo is 145 birds. The total population, wild and captive, in February 2007 was 498.
The Whooping Crane Recovery Teams of Canada and the U.S. were combined into the first International Recovery Team in 1995, with five Canadian and five U.S. members. The team decided in 2000 to write a combined international recovery plan. This is the third revision of the U.S. whooping crane recovery plan, which was first completed in 1980. In January 2005, the draft revised recovery plan for the whooping crane was published in the Federal Register for public review and comment. The final plan is under review.
Despite this progress, the wild whooping crane population is characterized by low numbers, slow reproductive potential, and limited genetic diversity. The possibility exists that a single catastrophic event could eliminate the wild, self-sustaining AWBP. Therefore, the principal strategy of the draft revised recovery plan is to augment and increase the wild population by reducing threats and establishing two additional, discrete populations.
Offspring from the captive breeding population will be released into the wild in an attempt to establish self-sustaining wild populations. The continued growth of the AWBP population, along with the two additional populations, will also stem the loss of genetic diversity.
Because of the whoopers' low numbers and growth potential, recovery criteria for the current plan have been established only for reclassification (downlisting) of the species. Downlisting can be achieved when 1) there are a minimum of 40 productive pairs in the AWBP and 25 productive pairs in each of two additional self-sustaining populations, or there are 250 productive pairs in the AWBP, and 2) there are at least 21 productive pairs in the captive population.
The whooping crane story is truly a classic in endangered species recovery. The beauty of these long-lived birds and their extreme peril of extinction captured the hearts of many people and ignited the sustained efforts of many individuals and organizations, from international governments to schoolchildren. These efforts have made it possible for the species to not only survive but begin to recover against tremendous odds.
Update: In a tragic loss on February 2, 2007, 17 juvenile whooping cranes were killed in their winter reintroduction pen at the Chassahowitzka NWR. These cranes had successfully completed their first migration, led 1,200 miles (1,930 km) behind ultra-light aircraft between Wisconsin and Florida. A violent line of thunderstorms and tornados that killed 20 people created a storm surge that flooded the release pen and caused the 17 cranes to drown. One of the penned birds escaped and was found two days later with sandhill cranes in an adjacent county. The numbers in the accompanying article reflect these losses.
The storm surge was unprecedented for that time of year and had not been forecast. Project personnel could not have reached the remote release site, which is accessible only by airboat, during the night-time storm. They will conduct a thorough review of the incident and change methodology to prevent such a loss from happening again.
Tom Stehn (firstname.lastname@example.org), the national whooping crane recovery coordinator, is stationed with the wintering cranes at Aransas NWR in Texas. Wendy Brown (email@example.com) is the endangered species recovery coordinator for the Southwest Region of the Service in Albuquerque, New Mexico.
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|Author:||Stehn, Tom; Brown, Wendy|
|Publication:||Endangered Species Update|
|Date:||Jan 1, 2007|
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