Coming Back On Its Own Terms
By expanding its range, North America's only native stork is slowly recovering from a century of swamp draining in South Florida
- Jeff Klinkenberg
- Apr 01, 1998
As winter slips into spring, biologist Shannon Ludwig boards a single-engine Cessna and takes flight. Soaring over the great Corkscrew Swamp Sanctuary in southwestern Florida, he counts nesting wading birds. He is especially fond of wood storks, which can make this work discouraging.
Last year was another troubled one for storks here at Corkscrew's 10,000 acres. The beleaguered species depends on just-right water conditions and an abundant food supply to reproduce. "We were doing okay for a while," Ludwig says. "But we had a drought that kept getting worse. Every time I flew I saw fewer and fewer chicks. We lost every one." Corkscrew was not alone. Wood stork nests throughout the Southeast suffered, apparently because of drought.
But even if the dry spell continues, scientists are hopeful about the future of North America's only native stork, which is recovering from a century of habitat destruction. The optimism is partly a result of moves toward improving water management in southwestern Florida, long considered the stork's most important continental nesting grounds. And if federal and state plans to restore the Everglades are successful, the resources might be managed even better in the future.
But the main reason for the stork's improving outlook has little to do with human intervention. "They're solving their own problems," says biologist John Ogden, who has studied storks for decades on behalf of Everglades National Park, the National Audubon Society and the state of Florida. In what scientists say is a surprising phenomenon, the storks increasingly are deserting their old colonies and raising their young in habitats to the north. During the last decade, they have been nesting in North Florida, Georgia and South Carolina.
In the 1930s, researchers estimated North America's wood stork nesting population at 20,000 pairs. In 1978, only 2,500 pairs were counted. Six years later, the federal government declared the U.S. breeding population of the wood stork endangered. But now about 5,500 nesting pairs exist, and if the number grows to 6,000, the species' status could be reclassified from the on-the-brink-of-extinction "endangered" to the slightly better off "threatened." If the birds recover even more dramatically, they could be taken off the list completely within a decade. "We're optimistic," says biologist Linda Finger, who has been coordinating the wood stork's recovery for the U.S. Fish and Wildlife Service. "We're seeing something new here. Wood storks are adapting to human-caused changes."
Among wading birds, wood storks stand out. They are white and black, with featherless heads. A full-sized adult measures about 40 inches tall. Other wading birds stalk prey, stop and strike, but wood storks seldom use their vision. Adapted to take advantage of South Florida's main habitat, the birds move their bills blindly back and forth through the water. When they feel something edible, they snap. If water is too deep, they have a hard time finding prey. If water is too shallow, their normal food supply--small fish, frogs and insects--may disappear with the water.
A stork egg hatches in about a month. A newborn chick weighs two ounces and is completely helpless and vulnerable to everything from heat to rain. A parent opens its wings like an umbrella and protects its young from the elements. Competition for food is fierce; often only the largest and most aggressive chick will survive. If food is in short supply, often the parents will abandon the nest.
When there's plenty of food, three or even four chicks have a good chance at survival. The parents take turns guarding the nest and hunting for food. With 5-foot wingspreads, the birds can reach altitudes of 1,000 feet or more, where they fly as far as 80 miles looking for ponds likely to be full of prey. While descending, a wood stork is an incredible acrobat, executing a series of dives, rolls and turns.
The most important wood stork habitat in North America--the Everglades, the Big Cypress and the adjacent Corkscrew Swamp--no longer offers the conditions to which wood storks have adapted. Ambitious developers started draining and logging after the Civil War, and things got worse in this century. When tropical storms flooded much of the lower peninsula in 1947, state and federal agencies got involved in the drain game.
By 1960, more than 1,400 miles of drainage canals and dikes crisscrossed the Everglades. Water was held in conservation areas for residents and farms; thirsty swamps had last dibs. During extraordinarily rainy years, water that would have helped wildlife was pumped into the sea. The Everglades lost again. All wildlife, especially wading birds, suffered. No wading bird suffered more than the wood stork.
The decline happened fairly quickly. In 1961, a famous year in wood stork annals, 6,000 pairs produced as astonishing 17,000 young. In 1968, another banner year, 5,000 nesting birds were parents to more than 7,000 chicks. Then South Florida suffered a series of droughts so severe that arsonists and occasional lightning strikes produced fires that burned the Everglades for weeks and even months. The new flood-control projects made a bad situation worse.
Unlike birds that are stimulated into reproducing by longer days, warmer temperatures and a more abundant insect life, wood storks get amorous when water conditions are right. They nest most productively during springs that follow rainy summers and autumns. When dry season begins in late fall, water levels drop. As months go by and water gets even lower, food is concentrated into small ponds where wood storks can reach it. That's the signal for the birds to nest.
If there's too little water, though, raccoons can reach nesting trees and eat the chicks. And even immature birds that survive predators have a hard time. During the ferocious droughts of the 1970s, adult storks had to fly farther and farther from the nests about a dozen times a day to find food for ravenous young. During the breeding cycle, a pair of wood storks needs about 400 pounds of fish to feed themselves and their young. The great wood stork crash commenced. "Some years we didn't produce a single chick," recalls Ed Carlson, manager of Corkscrew Swamp Sanctuary, which is operated by the National Audubon Society.
Water-sucking dredges or bulldozers will never knock down nesting trees in protected Corkscrew Swamp, the Big Cypress and Everglades National Park. But some of the best stork feeding areas are outside protected lands and frequently have been drained for agriculture or turned into housing developments and golf courses. "Wood storks have evolved to survive the occasional drought," Carlson says. "Boom or bust with storks, depending on rain, is natural. But the draining wasn't natural."
Because some water is required for successful reproduction, checking on wood stork chicks usually means wading. When biologists reach a wood stork's nesting tree and start climbing, the adults fly away, squawking. A scientist gently captures a chick, wraps it in a cloth to quiet it and descends the ladder. Then he or she lays the stork on a floating table, draws blood to test for contaminants and attaches a band around a leg.
"There is a lot we don't know," says U.S. Fish and Wildlife biologist Finger. For example, how did the birds expand into locations to the north? Storks always have foraged throughout the Southeast after nesting season. But nesting outside of the Everglades and the swamps of South Florida has been considered a rare phenomenon.
Then, two decades ago, someone found a stork nesting colony in North Florida. Scientists thought the colony was an interesting fluke, but more birds were discovered. As years passed, scientists became convinced that storks were definitely moving north during mating season. In 1980, nesting storks were discovered in Georgia. At the Savannah River Ecology Laboratory, University of Georgia biologist Larry Bryan has counted as many as 250 storks in three ponds that cover 25 acres at a former production facility for weapons-grade nuclear materials.
In 1981, nests were discovered near the Edisto River in South Carolina. "And we saw increases every year," says Tom Murphy, a South Carolina Department of Natural Resources nongame biologist. In a good season, 900 wood stork pairs produce 2,000 chicks. Private and state land-owners help by staggering the lowering of water in ponds. That way, parent storks, struggling to feed their young, can find abundant food over a longer period.
In 1988, wood storks arrived at Harris Neck National Wildlife Refuge near the Georgia coast. Now they're nesting nearby at Blackbeard Island National Wildlife Refuge. At Harris Neck, where black gum trees were dying due to unnaturally high water, scientists have built nesting platforms for storks. "We were amazed that they took to them so quickly," says biologist John Robinette of Savannah Coastal Refuges. In one astonishing year, storks used all 150 platforms. "Three-chick and four-chick nests were as common as dirt," Robinette says. "There are years when everything seems to come together."
Last year, with the worst drought in almost a decade in South Florida, parent storks couldn't find enough food for their starving chicks and abandoned nests. Things were a little better on the coast north of the Florida border, but barely. Low tides were essential for feeding; even in the wee hours of the morning, the wood storks were wolfing down minnows when the tide was low. They seemed to have enough food, but chicks still died. Scientists think newborn chicks may be unable to tolerate saltwater fish. If freshwater ponds dry too soon, chicks die. As the young birds get hardier, their systems apparently handle a saltier diet. "Another possibility is that since there are only two low-tide events in a 24-hour period, constraints on the timing and number of feedings might also limit breeding success," says Bryan. "We're still learning. Everything we find out is remarkable."
In South Florida, biologist John Ogden waits for his wood storks to return. He doesn't know what to make of the birds' recent northern movement. He wonders if what is happening in North Florida, Georgia and South Carolina means the Everglades has become a second-string nesting spot. Will the species permanently give up on what was once was the prime wood stork nesting grounds on the continent?
"I think the southern Everglades and the Big Cypress basins are going to continue to deteriorate," says Ogden, who represents his state's water-management district in Everglades restoration efforts. He adds, "At the same time, I do think that with restoration, the situation is going to get better. If that happens, it will be interesting to see what happens with the wood stork."
For the bird to recover completely--to be removed from the endangered species list--the Everglades and the Big Cypress ecosystems must be restored. "I keep telling those biologists in Georgia and in South Carolina," says Ogden, "that we're going to take our storks back from them."
Florida writer Jeff Klinkenberg is a columnist for The St. Petersburg Times.