Wood Stork

Mycteria americana

Description

The wood stork is a large (40 in; 102 cm), long-legged wading bird with an unfeathered gray head. It has a wingspan of 61 in (155 cm). Plumage is white with black flight feathers and tail. Immature birds have a feathered head, which, along with the neck, is grayish brown. Its bill, long and tapered to a blunt point, is large massive in comparison with the bills of herons and egrets. The legs are long and dark, while the feet and toes are pinkish in color and have shallow webbing between the bases of the toes. Like a crane, the wood stork flies with the neck fully extended, but it perches in trees, which cranes will not do. The wood stork is the only species of true stork breeding anywhere in the United States.

Behavior

Wood storks prefer to nest in the tops of large cypress trees growing in water. They are highly gregarious; as many as 25 nesting pairs have been observed in a single tree. The nest, which is added to each year, is a flimsy platform of twigs and sticks lined with finer materials. The average wood stork clutch size is three eggs. When the young hatch, they are scantily covered with down and are reared in the nest. If food is scarce because of drought, colonies often fail to breed. If rains are too heavy after the onset of breeding, colonies may abandon the eggs. The wood stork is largely mute. It feeds primarily on small fishes. The stork gropes in shallow water with an open beak, which it snaps shut when it feels its prey. Because feeding success improves with age and experience, young birds must spend twice as long foraging as mature birds.

Habitat

The wood stork usually nests in cypress and mangrove swamps along rivers and streams or adjacent to shallow lakes. Ideal foraging habitat is shallow wetlands that flood in the spring, producing an increase in the fish population. With the onset of summer the ponds begin drying up, concentrating fish for the catch. These drying periods typically correspond with the height of the nesting season.

Distribution

Historically, wood storks bred throughout the states along the Gulf of Mexico, from Texas to Florida, and along the Atlantic coast from Florida to South Carolina. The post-breeding summer range extended north to Arkansas, Tennessee, and North Carolina. Wood storks have been sighted incidentally as far north as Montana, Wisconsin, and New York. Researchers estimate that in 1930 there were about 60,000 wood storks in the U.S. breeding population (40,000 adults and 20,000 non-breeding immatures). Censuses in 1960 located 10,060 breeding pairs. Between 1960 and 1975 the U.S. breeding population declined 41% to 5,982 pairs. This decline continued until 1980, when the number of breeding pairs stabilized at about 4,800. Other breeding populations from Mexico to South America appear stable and are not endangered. Wood storks from the Mexican west coast are regular post-breeding migrants in California and Arizona; those from rookeries in eastern Mexico are seen in Texas and Louisiana. Breeding populations in the United States are restricted to Florida, southeastern Georgia, and South Carolina. Major rookeries are concentrated on the Florida peninsula and extreme southeastern Georgia. Estimates of the breeding population have held fairly steady since 1980. In 1986 the National Audubon Society estimated that there were 5,850 breeding pairs in U.S. rookeries. Since mid-1985, the U.S. population has ranged between 5,500 and 6,500 pairs.

Threats

Although many of the wood stork's breeding sites in southern Florida remain largely undisturbed, nesting attempts in these areas have failed repeatedly in recent years because of inadequate or insufficient foraging habitat. Suitable foraging areas in south Florida have decreased by about 35% since 1900 due to wetlands alteration, such as construction of levees, canals, and floodgates.

The traditional rookeries in South Florida's Everglades National Park, and the National Audubon Society's Corkscrew Swamp Sanctuary are secure in the sense of being protected from disturbance, but nearby foraging areas have been drastically modified by residential and commercial development. Nesting success then depends on feeding areas that are far from the rookeries. For this reason none of the wood stork rookeries can be called truly "secure." Raccoon predation has also been a problem at central Florida rookeries. In 1981, raccoons destroyed all 168 wood stork nests at a rookery in Hillsborough County when water levels dropped low enough under nest trees to provide access for the predators.

Conservation and Recovery

When the wood stork was officially listed as endangered, the Department of Energy (DOE) was forced to examine the environmental impact of operating a nuclear reactor on the Savannah River, south and east of Augusta, Georgia. A way was devised to prevent thermal pollution of the river, but reactor operation was expected to raise water levels downstream to the point that the foraging habitat would be unusable by wood storks. The DOE agreed to construct an artificial foraging area to replace the habitat that would be lost when the reactor came on line.

The site selected for the artificial habitat was Kathwood Lake, a dry lake bed at the National Audubon Society's Silverbluff Plantation Sanctuary near Jackson, South Carolina. The U.S. Fish and Wildlife Service, the National Audubon Society, the DOE, the Soil Conservation Service, Auburn University, the Savannah River Ecology Lab of the University of Georgia, and a major area contractor (E.I. duPont de Nemours) all worked together to design and build the habitat, which was completed in 1986. In July, the wading lake was stocked with fish from the Orangeburg National Fish Hatchery, and local storks discovered it soon after. Within a week, more than 70 storks were actively foraging in the lake.

Many private land owners and public land managers have since requested details of the Kathwood Lake design in order to reproduce it in their own areas. This successful collaboration is serving as a model for other attempts to provide wood stork foraging habitat.

In June 1989, the Interior Department created a new wildlife refuge for the Florida panther and other endangered species in south Florida. The 30,000-acre (12,140-hectare) Florida Panther National Wildlife Refuge is adjacent to the Big Cypress National Preserve and provides protected habitat for the Endangered Everglade snail kite (Rostrhamus sociabilis plumbeus ), bald eagle (Haliaeetus leucocephalus ), peregrine falcon (Falco peregrinus anatum ), and eastern indigo snake (Drymarchon corais couperi ), as well as the wood stork.

In 1997, a revised recovery plan for the U.S. breeding population was released to update the original information and to address new threats and needs. Many tasks identified in the original plan have been accomplished and more information is now available on the biology and distribution of storks throughout the southeast.

According to the revised plan, reclassification from endangered to threatened could be accomplished when there are 6,000 nesting pairs and annual regional productivity greater than 1.5 chicks per nest a year (calculated over a three-year average). Delisting would be accomplished when there are 10,000 nesting pairs calculated over a five-year period beginning at the time of reclassification to threatened, with annual regional productivity greater than 1.5 chicks per nest a year, and a minimum of 500 successful nesting pairs in South Florida.

Under an ideal set of circumstances, the earliest possible date for complete recovery of the population would be 2005. However, because of the time necessary to complete some of the long-term restoration tasks, full recovery may not be possible for an additional 15-20 years.

Contact

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

References

Kushl an, J. A., and P. C. Frohring. 1986. "The History of Southern Florida Wood Stork Population." Wilson Bulletin 98: 368-386.

Ogden, J. C. 1985. "The Wood Stork." In R. L. Di Silvestro, ed., Audubon Wildlife Report 1985. National Audubon Society, New York.

Ogden, J. C., and B. W. Patty, 1981. "The Recent Status of the Wood Stork in Florida and Georgia." Technical Bulletin WL5. Georgia Department of Natural Resources/Game and Fish Division, Atlanta.

Ohlendorff, H. M., E. D. Klaas, and T. E. Kaiser.1978. "Organochlorine Residues and Eggshell Thinning in Wood Storks and Anhingas." Wilson Bulletin 90 (4): 608-618.

U.S. Fish and Wildlife Service. 1986. "Recovery Plan for the U.S. Breeding Population of the Wood Stork." U.S. Fish and Wildlife Service, Atlanta.

U.S. Fish and Wildlife Service. 1997. "Revised Recovery Plan for the U.S. Breeding Population of the Wood Stork." U.S. Fish and Wildlife Service, Atlanta.