Everglades National Park

Wood Stork

We have a bird in Everglades National Park that is an excellent messenger of the past, present, and future. We call a bird that carries this role an indicator species, because its rather specific habitat requirements are so closely associated with one particular environment. The quality and quantity of that required environment directly determines the well-being and the number of that species. Since it is usually much easier to count and record the biology of one or more indicator species than it is to measure the more complex workings of an ecosystem, close monitoring of the properly selected species will tell us much about the health of the entire system.

In this case, the bird is the wood stork, and the environment is the Florida Everglades. Like the wood stork, the Everglades ecosystem is now endangered. Storks were once more abundant in the southern Florida wetlands than in any other region throughout the southeastern states. The wood stork should thrive in the Everglades and Big Cypress because it is a specialized species that does best in tropical and subtropical zones with distinct wet season/dry season climates. A stork locates food, mostly small fresh water fish, not by sight but by groping with its bill in shallow water. This feeding technique is most effective when water levels are dropping throughout broad marshes as a result of prolonged dry periods, and fish are being concentrated in ever-diminishing pools.

The Everglades of the 1930s, largely undrained and without complex water control structures, supported a nesting population of approximately 4,000 pairs of wood storks. Modern water control programs in south Florida have so greatly changed the flooding and drying patterns of the Everglades, however, that the very survival of stork nesting colonies in the park is in question. Although the number of storks in Everglades colonies remained as high as 2,500 pairs as recently as 1960, accelerated development of water control structures and unnatural water delivery schedules have sharply increased the birds' decline during the past 30 years. By the mid-1980s, only 250 pair of wood storks were still nesting in Everglades National Park!

The stork's indicator role has been dramatically demonstrated, as total numbers of all species of wading birds nesting in mainland Everglades colonies have also dropped during this same 30 years from an estimated 40,000 to 9,000 pairs. Since the 1930s, the decline in all wading birds has exceeded 90 percent!

Clearly, the southern Everglades ecosystem has been incapable of supporting viable populations of wood storks and other wading birds for several decades. While the storks have been chronicling the deterioration in the ecosystem, at the same time they are providing information that is needed for the system's restoration. Our understanding of the habitat requirements of wood storks makes it possible to revise water management practices in order to restore good wading bird feeding conditions. The challenge, however, is to implement these improved water management programs in the face of the rapidly growing human demands for water and space in southern Florida.

Endangered wood storks have declined from 6,000 nesting birds to just 500 since the 1960s. If recent trends continue, wood storks may no longer nest in South Florida by the year 2000.

Their feeding behavior explains their predicament. Wood storks feed not by sight but by touch "tacto-location" in shallow and often muddy water full of plants. Fish can't be seen in those conditions. Walking slowly forward the stork sweeps its submerged bill from side to side. Touching prey, mostly small fish, the bill snaps shut with a 25 millisecond reflex action, the fastest known for vertebrates. Only seasonally drying wetlands concentrate (mostly in drying ponds) enough fish to provide the 440 pounds (200 kg) a pair of these big birds requires in a breeding season. When natural wetlands cycles are upset by human water management, wood storks fail to nest successfully. The wood stork—which stands over three feet (0.9 meters) tall, has a five foot (1.5 meter) wing spread, and weighs four to seven pounds (1.8 to 3.2 kg)—was placed on the federal Endangered Species list in 1984.


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