Species at Risk

Wood Storks Grope for Wetlands
by Susan D. Jewell, U.S. Fish and Wildlife Service

They'll eat fish, amphibians, reptiles, crustaceans, mammals, birds, and arthropods—alive or dead, day or night—in roadside ditches, pristine Everglades marshes, cow ponds, cypress swamps, golf course water traps, and estuaries. So, with all those opportunities for success, why is the wood stork listed as endangered in the United States?

It took poaching in breeding colonies from Texas to South Carolina a hundred years ago, followed by a century of draining, pumping, rerouting, and polluting the surface water on their habitats, topped off with a generous dose of development. While there are no good estimates of stork numbers before the pressures began, the population in the 1930s was estimated at 15,000 to 20,000 pairs. By the early 1980s, the stork population in the United States had declined to around 5,000 nesting pairs, and its breeding range had shrunk to Florida, Georgia, and South Carolina. The bird was listed in February 1984.

Nesting initiates in southern Florida around December and in northern Florida, Georgia, and South Carolina around March. Nesting habitat is versatile, from low-lying mangroves to stately bald-cypresses. The birds' foraging habitat requirements are simple: relatively calm, shallow water (2 to 16 inches deep) with little aquatic vegetation. The water can even be murky, because a common method of foraging is by groping. The stork swirls its long bill, slightly agape, back and forth through the water and snaps it shut instantly upon touching a prey item. This tactolocation technique allows the bird to forage at night.

As versatile as their foraging habits may be, there are limits. Wood storks are soaring and gliding birds, depending on thermals to stay aloft using minimal energy. They can range great distances, often as far as 60 miles or more daily, from their roosts or nesting colonies to locate food, but the farther they have to search for food, the less time they have to feed.

Particularly in their former stronghold of south Florida, storks depend on slowly decreasing water levels for feeding during the nesting season. Under natural conditions, water levels start dropping at the start of the dry season around November, when rainfall decreases and evapotranspiration is still high. Groping becomes more efficient as aquatic prey species concentrate in the remaining water. Conditions have not been natural, and therein lies the problem. Surface water has been manipulated to such an extent in Florida, for example, that the stork's requisite wetland conditions have, for the most part, been lost.

However, with the ecosystem restoration occurring in the Florida Everglades and Big Cypress, there is good news on the horizon. Downlisting to threatened status is moving closer to reality. The stork's recovery plan calls for an average of 6,000 nesting pairs and an annual regional productivity of at least 1.5 chicks per nest per year over a 3-year period. Survey numbers, which are incomplete for Florida due to lack of funding, hint that the number of breeding adults needed probably has been reached. All that is needed now is for surveys to show those birds nesting successfully 3 years in a row.

For more information, contact Billy Brooks, U.S. Fish and Wildlife Service, 6620 Southpoint Drive South, Jacksonville, Florida 32216, (904) 232-2580 extension 104, billy_brooks@fws.gov.