As the mallards invaded what was once black duck territory, the two closely related species began mating—and producing fertile offspring, an indication that the species difference was not all that great. This "swamping" of the black duck gene pool was abetted, with all the goodwill in the world, by many conservation groups and some states, which released pen-raised mallards into the wild along the flyways. During the past decade, Maryland alone released about 15,000 mallards a year, a program mandated by law. This despite the fact that the state's winter survey of blacks had plummeted from 149,000 in 1956 to a scant 16,900 this year.
Collections of wings from birds killed by hunters have shown that as many as 15% of the so-called mallards and blacks being shot were actually hybrids. Experienced waterfowlers can tell the hybrids at a glance: There is a mallard-like green sheen to the drake's head feathers, and the bright red feet from which the blackie derives it specific epithet (rubripes is Latin for "red foot") are often a rather sickly orangish yellow. But the 15% figure may be a low estimate, at least on some stretches of the Atlantic Flyway. Though mallards have declined by 28% since the 1960s at the southern end of that flyway, they are up 94% in New England, 29% in Maryland and Virginia and a whopping 115% along the New York-New Jersey shore and in Pennsylvania.
"The mallards are thriving in areas that were classic black duck wintering grounds," says Smith. "These mallards are prairie ducks bred up in Ontario and Quebec, coming down the Atlantic Flyway to winter over where they rarely were seen before. It's not surprising that the biggest increase has been in New Jersey. The Jersey marshes have held their quality much better than the Chesapeake, which collects detritus flowing down the Delaware River system."
Kill figures underscore the population change. In the 1970s, New England hunters killed twice as many blacks as mallards. Now, the kill figures are about even in what is one of blackie's last strongholds south of the Canadian border. In New York, New Jersey and Pennsylvania, hunters in 1983 killed 200,000 mallards to 63,000 blacks. In Delaware, Maryland, Virginia and West Virginia, 114,000 mallards were shot versus 32,000 blacks, while in North Carolina, South Carolina, Georgia and Florida, the numbers were 90,000 mallards, 18,000 blacks. Biologists say kill figures may approximate a quarter of the total population of any duck species. Thus, there may be about 1.6 million mallards currently using the former black duck range for various purposes, including mating. Last spring conservation writer George Reiger observed a mallard drake courting lustily at least two black duck hens on his pond near Locustville, Va. As Reiger explains, pair-bonds among ducks are established during the winter, long before the birds move north to their breeding grounds. If a mallard drake pairs with a black duck hen somewhere down in Virginia, he will follow her to the Northeast. There he will be exposed to a wealth of mating opportunities with other black hens. The danger here, as many biologists see it, is that the resultant offspring of a black duck-mallard cross could lose the genetic immunity to leucocytozoan infestation peculiar to the black. If so, many of the young would not survive the blackfly country to wing south as juveniles in the fall. This loss could account for some of the slow, steady 1.5% to 2% decline in black duck numbers cited by Smith.
"But I know of no study that shows the crosses losing immunity," Smith says. "Indeed, perhaps we're seeing the creation of a superhybrid. A kind of 'hymallard' that's as likely to be found on a lonely backcountry beaver pond as on the Reflecting Pool of the Washington Monument."
Watermen on the Eastern Shore speak with awe of a "giant" race of black ducks they sometimes see—huge, bright-footed birds nearly the size of geese—and it has long been believed that there is indeed a "maritime" race of the birds that rarely ventures far south of its home range in Labrador. Yet Smith feels that size is merely an indicator of age among black ducks. A licensed Canadian duck trapper for years has been sending Smith bands taken from outsized black ducks he's caught and released. The bands are timeworn to near illegibility, proving that the big birds are also old birds. "The biggest black duck I ever shot," Smith says, "was on a river in Tennessee. It's unlikely he flew there from Labrador."
Another possible cause of the ongoing black duck decline might well be acid rain. The bird's Northeast breeding grounds are directly in the path of weather systems carrying sulphur dioxide from the smokestacks of the industrial Midwest. Just as hundreds of high-country lakes in the Adirondacks and Vermont's Green Mountains have found their pH levels plummeting to the acid end of the scale, and consequent lifeless-ness, so too have many ponds and lakes in Maine and the Maritimes. Though acid rain by itself would not kill the black ducks, it could kill off enough of the food in the ponds where their broods mature to slow growth and cause weakness, even starvation.
At the same time, down in Laurel, Mike Haramis, a waterfowl biologist at the Patuxent Wildlife Research Center, is conducting an experiment that shows the effect of acid rain on 10-to-20-day-old black ducks. Last spring Haramis and some colleagues raised six separate broods of black ducks on three pairs of different man-made ponds. The ponds, which are 40 feet in diameter and a maximum of 2½ feet deep, are bottomed in 10 inches of topsoil over plastic, and have antipredator nets rigged overhead "to keep out the owls." One pond in each pair is maintained at a highly acid pH of 5, the other at an essentially neutral pH of 7. The young ducklings eat animal matter during their first few weeks of life, snapping up nymphs and other larvae that swim in their natal waters. Of a dozen young birds raised on a nonacid pond, 10 gained weight and two maintained their weight. Of the birds raised on an acid pond, three maintained their weight, six lost weight and three died.
What's more, as Haramis points out, the ducklings in the "stressed" environment, i.e., the acid pond, were more likely than their better-fed relatives to go off on their own in search of food, thus abandoning the security against predators that comes with flock behavior, or what biologists call "brood integrity." "They're also much less selective in what they'll eat," he says. "I've seen them ingest mud and other nonorganic material that does them no nutritional good. You'll see them truckin' through the uplands, eating grass, or off alone by themselves in the deep woods." In short, translated to a natural scene, easy pickin's for a sharp-eyed hawk, fox, coyote or owl.
It may well be that the black duck's drift toward extinction is the result of what biologists call a synergistic process—a combination of adverse factors working together to achieve an end that no single one could accomplish. Loss of habitat and the widespread use of pesticides 30 years ago may have triggered the decline, and while subsequent legislation to protect the wetlands and the ban on DDT in 1972 were attempts to halt those processes, the worst damage had already been done.