Millions of migrating ducks, geese and other waterfowl will find fewer rest stops on their way south this fall — more fallout from a drought that has parched marshes, ponds and wildlife refuges on flyways between North and South America.
Hurricane Isaac and its remnants are dumping heavy rains from the Gulf Coast to the Great Lakes, helping waterfowl conditions in the Mississippi and Ohio river valleys, but the storm missed drought-ravaged portions of the Plains and western USA, where ponds and refuges have dried up.
Waterfowl populations are up, and healthy birds are coming off several lush years in prairie-pothole nesting grounds in Canada and the northern USA. The drought hit after robust hatches in the spring, when adequate water was present in the nesting areas, and late-August rains have helped. But conditions are so severe and widespread that migrating flocks have little margin of error, especially if drought continues into spring.
Biologists say cyclical drought is a necessary hardship for migrating birds because it kills predatory plants and animals that threaten the complex ecosystem they live in.
“Wetlands are really, really dynamic,” says Dale Humburg, chief biologist for Ducks Unlimited, which helps boost waterfowl populations for hunters and birdwatchers. “They need to dry, periodically, to maintain their productivity. Otherwise they stagnate and don’t produce the food that birds need, year after year.”
But some biologists worry that this drought is a product of climate change that is forcing animals to rapidly adapt and that the steady loss of wetlands to human encroachment is making that even harder.
“Obviously, there is something going on, on a far bigger scale outside of what we deem normal,” says Bill Waln, co-interim manager of the Quivira National Wildlife Refuge in Kansas, a normally vital stopover point for tens of thousands of migrating geese, ducks and the endangered whooping crane.
Quivira’s 35 square miles of ponds and marshes were mostly dust-dry after a brutally hot and dry summer. Isaac was too far east for relief. A late-August rain helped replenish some ponds, but excessive heat has evaporated much of it, and managers are worried the refuge will be dry when the bulk of the migration comes in October.
“I don’t want to be a glass-half-empty guy, but we need three or four more events like this just to break even,” Waln says.
Birds that would normally drop in to “rest up a little bit, fuel up so they can make the rest of the trip south” this fall may have to “just keep flying south, looking for something,” he says.
The whooping crane breeds in Canada and the northern USA and winters in Florida and Texas. Some use Quivira as an important rest stop in the migration back and forth. Waln hopes the refuge can count on some fall water replenishment as water tables rise after farmers in western Kansas stop irrigating, although this drought has been so severe that normal rise may be endangered.
For teal and other birds already moving south, the stress is on now.
Not only are major refuges parched, but the farm crops that are normally banquet fields for migrating flocks are wiped out or diminished.
“In a normal year, they would kind of hopscotch down the flyways,” Humburg said. “In a year like this, there are really going to be a limited number of locations they will find en route.”
Isaac, he says, will provide “regional improvements in habitat conditions that undoubtedly will need additional rains to sustain improvements into the fall and early winter.” But it’s too late, he says, to improve food conditions for migrating birds.
Biologists are worried that birds still stressed from the fall migration to the Gulf Coast and Central and South America could find worse nesting conditions when they head north next spring.
The Fish and Wildlife Service’s annual May aerial survey of 2 million square miles of nesting areas in the U.S. and Canada estimated the duck population at 48.6 million, up 7% from 2011, and 43% above the average since 1955.
The survey said there were 5.5 million ponds in its survey area, which stretches from Alaska to the northern Plains and Great Lakes to New Brunswick, Canada. Overall, that was 32% below 2011, but still above the long-term average.
But the northern Plains of the USA was drier, with 49% fewer ponds than the year before. The Fish and Wildlife Service defines a pond as any body of water at least 6 inches deep in June. Potholes, water-catching basins that often are no larger than a suburban back yard, are crucial to the reproduction and survival of young waterfowl.
FWS Director Ashe says that besides stress on migrating birds, the drought has produced troubling fishkills in the Mississippi and Missouri rivers.
But in some places, drought-induced fishkill is good news.
Wisconsin’s Horicon Marsh, a 52-square-mile wildlife haven jointly managed by the state and the Fish and Wildlife Service, had planned to reduce water levels in some areas of the refuge even before dry weather hit. If marshes get too deep, plants that the birds depend on can’t grow. Some species of shorebirds thrive in mudflats.
The drought helped reduce water levels, aiding a “rejuvenating” of the marsh, says Horicon project leader Steve Lenz. “It killed off a whole bunch of common carp that we didn’t want in the marsh,” Lenz says.
Biologists say those bottom-feeding fish are bad for wetlands because they churn up beds necessary to grow submerged plants that waterfowl depend on for food.