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WOOD STORK (Mycteria americana)

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Wood stork picture
Family: Ciconiidae

Order: Ciconiiformes

STATUS: Endangered

DESCRIPTION: The wood stork is the only stork species that breeds in North America. It is a large, long-legged wading bird, about 110 centimeters in height, with a wingspread of up to 165 centimeters. The plumage is white, except for black primaries and secondaries, and a short black tail. The head and neck are largely unfettered and dark grey in color. The bill is black in adults and yellowish in juveniles and subadults. The feet are flesh-colored, becoming bright pink on breeding adults. Males are usually larger than the females but are identical in appearance. Immature birds resemble the adults, but have a lighter-colored head.

HABITAT AND DISTRIBUTION: Storks are birds of fresh- and brackish-water wetlands. They commonly feed in freshwater marshes, flooded pastures and ditches, and nest in cypress or mangrove swamps. Particularly attractive feeding sites are depressions in marshes or swamps where fish become concentrated during periods of falling water levels. At one time the wood stork may have bred in all the coastal southern states from Texas to South Carolina. The United States breeding population is now restricted primarily to Florida, excluding the Keys, and extends north to southern Georgia and south through Central and South America to northern Argentina. Several valuable nesting colonies lie within the Everglades National Park, Corkscrew Swamp Sanctuary, and the Pelican Island and Merritt Island National Wildlife Refuges. Less than 10,000 wood storks inhabit Florida at present.

LIFE HISTORY AND ECOLOGY: The wood stork is a colonial species, nesting in large "rookeries" and feeding in flocks. Successful nesting in South Florida most often occur in years when rookeries form from November through January, and young fledge before summer rains in June. The smaller Central and North Florida rookeries form during February through April, and fledge young during summer. Nests are frequently located in the upper branches of large cypress trees or in mangroves on islands, with several nests usually located in each tree. The nests are constructed of sticks and vines and are lined with green leaves or cypress sprigs. Storks lay 2 to 4 eggs, and average about 2 fledglings per successful nest. Eggs and nestlings are subject to predation. Nests can fall or be blown from the trees, where eggs and young birds may be eaten by waiting alligators attracted by the rain of debris from the rookery overhead. Mortality rates

are high in the first year fledglings, particularly if food is scarce or rains come too soon. Wood storks achieve sexual maturity at the age of three or four and begin nesting successfully at the age of five. Storks utilize a special, tactile method of locating food, known as grope-feeding: as the stork probes with its beak in shallow water, the small fish that come in contact the partially open beak are captured. This feeding method requires a high consumption rate of fish. Wood storks pursue ponds with concentrated fish populations effected by dry season conditions. As the ponds dry out the wood storks will migrate from upland ponds to lowland ponds. Storks routinely use thermals to soar distances up to 130 kilometers one-way between rookeries and feeding sites. When not involved in feeding or nesting, storks spend hours each day inactively perched in roosting trees or on the ground.

BASIS OF STATUS CLASSIFICATION: Until the last few decades, wood storks were a common sight in the wetlands of Florida, largely because they were spared by the plume hunters that decimated many of Florida's wading bird populations at the beginning of this century. It is estimated that in the south Florida area, the wood stork population has decreased by 75 percent from 1967 to 1982. This drastic population drop is due to decreased reproduction caused by destruction and disturbance of suitable habitat. Populations are continuing to be stressed due to drought conditions and altered hydrology caused by water management and development practices. Seasonal water levels have been reduced so that there is not an adequate food supply available during the nesting season, which typically occurs between November and January. The decline in storks, at least in south Florida, has been due to almost routine nesting failures brought on by limited feeding conditions for storks in the much-manipulated south Florida wetlands. In response to this drastic decline, the federal government in 1984 classified the wood stork as an "endangered" species. The wood stork is also protected under the Migratory Bird Treaty Act of 1981.

HABITAT GUIDELINES: Protection of this species consists of providing an effective zone that buffers the nesting sites. This "buffer zone" may extend into upland habitat. The extent of these buffers is based on existing State and/or Federal guidelines, or reflect the recommendations of the Florida Game and Fresh Water Fish Commission.

Any activity proposed within a buffer zone would be subject to review. Activities that could be allowed in the buffer zone would be those activities which would not have any long term detrimental impact on the nesting birds. The following would be considered when making this determination: (1) the type of activity or construction planned and its' long term impacts; (2)

the nature of the natural community that makes up the buffer zone (does it provide a visual barrier for any proposed nesting activities?); and (3) the timing of the proposed construction (does it occur outside the nesting season?).

RECOMMENDATIONS: We know enough about the biology of the wood stork to know why it is in decline and what needs to be done. The difficulty is that the wood stork's decline is related to habitat loss and, therefore, solutions have economic, social and political impacts. How to implement a recovery in the face of ever increasing demands for land and water for agricultural, industrial and residential uses is still an unanswered question. Listing of the species as endangered was a first step in the recognition of the problem. A second step could be the implementation of the standard set of guidelines which directs the Game and Fresh Water Fish Commission and U.S. Fish and Wildlife Service in dealing with developments that threaten nesting wood storks. These guidelines call for establishing protective zones around wood stork nests, within which certain restrictions, from no disturbance at all to confining development activities, are imposed. Usually, the no-disturbance zone extends from 0.30 to 0.46 kilometers around a given colony, depending on the amount of visual screen (tall trees) surrounding the colony, with a less restrictive zone extending an additional 0.30 to 0.76 kilometers outward. A third step could be continued research, monitoring of colonies, water management, and acquisition of important nesting areas are high priorities.

To solve the problem of wetland disruption, however, will require the coordinated efforts of water management districts, federal, state, and local governments and the support and understanding of the public. Wood storks are so closely attuned to the natural cycles of Florida's wetlands that their well-being is an indicator of the health of out wetlands themselves. The disappearance of the wood stork would signal the loss of a valuable resource.

Florida Power & Light Company. 1989. Florida's wood storks. 26pp.

Ogden, J.C. 1978. Wood stork. Pp. 3-4. In H.W. Kale, II, (ed.), Rare and Endangered Biota of Florida. Birds. University Presses of Florida, Gainesville, FL.

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, GA. 28pp.

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