America's prairie waterfowl, their numbers already depleted by decades of agricultural development and lost habitat, are seriously threatened this summer by the worst drought since the Great Depression.

North Dakota, cited by the Agriculture Department as suffering more from the searing heat than any other state, is at the heart of the prairie pothole region, a 300,000-square-mile patch of glacial gouges that is a critical stop on the Central Flyway for migrating and nesting birds.In a landscape resembling a vast piece of Swiss cheese, the potholes trap precious freshwater that creates the food and shelter for birds trying to reproduce.

About 50 percent of all ducks in North America come from the prairie potholes.

But this year, because of record-breaking heat, a drastic drop in annual rainfall and a barren, dry winter, the U.S. Fish and Wildlife Service estimates the duck population in North Dakota is down 18 percent from last year and has decreased 22 percent in South Dakota since 1987.

Federal counters estimate North Dakota has 2.4 million ducks and South Dakota about 2 million.

Further, say Fish and Wildlife aerial surveyors, there's been a sharp decline in the number of waterholes available to those birds attempting to hatch young.

In North Dakota, the pond count is down 49 percent from last year; in South Dakota the number of available waterholes has shrunk 42 percent.

`We've put transmitters on about 175 female mallards in North Dakota and Minnesota this season, and so far only five have hatched broods," said Gary Krapu, a federal research biologist at the Northern Prairie Wildlife Research Center in Jamestown.

"It's likely fewer than 20 of those hens will produce broods this season."

"If the drought lingers and populations continue to decline, Americans can expect to see far fewer waterfowl than they have traditionally known," Krapu said.