Bird of Grace and Trauma
Snowy egrets once narrowly escaped extinction; now pollution is threatening their future
They are among the most graceful and showy of all North American birds. And if recent discoveries regarding their expanding range are any indication, snowy egrets also may be among the most adaptable. Hunted to near-extinction a century ago, the regal birds have since recovered and moved into new territories. They now nest in the most unlikely locations, including, of all places, congested New York Harbor.
"It's incredible to think that egrets are surviving and raising chicks here," says biologist Katharine Parsons, referring to the pollution-choked waterways off Manhattan. "These birds are pioneers."
For scientists like Parsons, who has studied the behavior of wading birds along the Atlantic Seaboard for more than a decade for the Manomet Bird Observatory in Massachusetts, there is both good news and bad regarding snowy egrets.
The good news is that the graceful birds are now breeding as far north as Maine and southern Canada. Researchers are finding them in areas, says Parsons, "where they had never bred before, at least not since the last Ice Age."
The bad news is that wetlands development and pollution in parts of their expanding range threaten to undermine this recovery in the years to come. Such development has already reduced the birds' numbers by nearly 95 percent in Florida since the turn of the century. And now, new evidence suggests that snowy egrets may be among the most vulnerable birds when it comes to pollution.
"Snowies apparently don't have the ability to modify their foraging behavior in the face of a pollution event like an oil spill," observes Parsons. "They don't seem to be able to detect a decline in the quality of their prey, or to figure out that their chicks are not doing well." The overall effects of such behavioral deficiencies are not precisely known, she adds, "but you can speculate that they might prove to be disastrous."
Snowy egrets are no strangers to disaster. Members of the heron family, they once nested cheek-by-jowl with as many as 10,000 other herons and egrets, from the tropical Caribbean to as far south as Argentina and as far north as California in the West and New Jersey in the East. In the latter part of the nineteenth century, though, the birds had the misfortune of being discovered by the fashion-conscious femmes of urban America and Europe. Snowy egret plumes began appearing on hats, fans, capes, dresses and even muffs. Knowing that the approachable snowies were easy prey, poachers were happy to continue supplying the demand for the large white plumes.
By the turn of the century, the birds were rarely sighted along the Eastern Seaboard farther north than Florida and Georgia. Fortunately, public sentiment changed, and so did the laws. In England, Queen Victoria forbade British soldiers from wearing egret feathers in their hats. In this country, the U.S. government passed the federal Migratory Bird Treaty Act in 1918. In its wake, snowy egret hunting came to a virtual halt.
Thus protected, the birds began to expand their eastern range again, with successive generations of young egrets relentlessly forging new and ever more northerly colonies. By the mid-1950s, they were breeding on remote stretches of Long Island and in the marshes of Cape Cod. Eventually, some 300 breeding pairs of snowies settled down with other heron species to nest on estuarine islands in the middle of New York Harbor.
There, according to Manomet researcher John Brzorad, who, with Parsons, undertook a study of the heron colony, "you'll find birds feeding in the most unusual areas—drainage ditches near airports, wastewater areas near petroleum refineries, areas where none of us expected to find them."
The study, initiated in 1985 and funded in part by the U.S. Environmental Protection Agency, will continue for at least 30 years. The results will greatly increase the scientists' ability to understand the relationship between the birds and their unusual environment. "There has been a lot of legislation designed to clean up New York Harbor," says Parsons. "Over 30 years, we hope we will be able to document the recovery of the ecosystem."
At the same time, this means snowy egret behavior is becoming increasingly understood. "We didn't know much about them before," says Parsons, "because they've never been studied so intensively."
When they return to the East Coast from their wintering grounds in the Caribbean, male snowy egrets immediately stake out their nesting sites, often reestablishing themselves in the same trees they used the previous year. In fact, their subsequent mating displays—cued, some experts think, by the earlier dances of other heron species in the colony—often end up attracting last year's mate. (Egret couples do not stay together during winter.)
Once the nest is ready and the eggs are laid, mother and father take turns incubating them. The relatively idyllic brooding period comes to an end with the birth of the chicks. Insatiably hungry from day one, the infant egrets demand food by grabbing their parents' bills with their own bills and tugging. The harried parents respond by regurgitating a meal of partially digested fish. The chicks' bill-grabbing behavior is a vital biological cue, for in the absence of the demand, the parents will not feed the young.
About three weeks after birth the chicks begin to leave the nest for brief periods. A week or so later, they make their first flights, the symbol of approaching adulthood. For the rest of the summer and early fall the young egrets feed, stirring up fish in the shallow waters of estuaries or marshes by raking the bottom with their feet or agitating the water with their bills. As the weather gets colder, they begin migrating south, heading for wintering grounds on the Gulf Coast, in the Caribbean, or, for those egrets that breed in the western United States, in Mexico.
Unfortunately, both in the United States and abroad, the birds' wintering grounds are rapidly disappearing. "This is the biggest problem they face," says Parsons. "The rate of wetlands loss in this country is unacceptable. But in other countries—especially in South America, where people are constantly converting mangrove swamps to agriculture—it's catastrophic."
Another source of potential catastrophe are the handmaidens of development: industrial and agricultural pollution. Pesticides sprayed on farm crops, for example, can be devastating. As recently as 1988, investigators in California's Imperial Valley and in Oregon reported finding residual levels of the pesticide DDE in the eggs of great egrets. "It only takes 8 parts per million of DDE to have an impact on reproduction," says wildlife biologist Harry M. Ohlendorf, formerly of the University of California at Davis. "But in eggs in the Salton Sea in Southern California, we found levels as high as 24 parts per million."
Although these figures are for great egrets and black-crowned herons, "it seems likely," says Ohlendorf, "that snowies would be in the same ballpark." At these levels, DDE thins eggshells, causing increased breakage.
Although all birds are vulnerable to pollution, species at the top of the food chain, like herons and egrets, are more vulnerable, says Parsons, "because the pollutants are more concentrated in the fat cells as you go farther up the chain. So those birds end up getting larger concentrations than, say, ducks, which eat vegetation that may be contaminated, but not in such a heavily concentrated way."
In fact, new evidence suggests that snowy egrets may be more susceptible to pollution than most other birds. Parsons has found that of all the bird species in the marine environments surrounding New York City, snowies were the most severely affected by last year's massive oil spill there. "Snowies continue to go to the same feeding spots, even when those spots have been significantly degraded," she says.
Parsons and her coworkers will continue to monitor the birds, hoping to determine the degree to which pollution affects the birds' ability to reproduce. Meanwhile, she considers their very presence there as cause for cautious optimism. The New York Harbor egrets may be a sign the birds can survive and even flourish despite the sometimes negative influence of Homo sapiens.
"I hope we'll be able to coexist with the egrets in a generous and peaceful way," she concludes. "I think they're here to show us that it's possible."
Massachusetts journalist Bill Lawren wrote about our fickle love affair with plastic in the October-November 1990 issue. Tennessean John Netherton photographed the egrets in northern Florida.