There’s been another massive bird die-off, this time in South Dakota. But while the blackbird & fish deaths in Arkansas that captivated the nation turned out to have most likely been a result of natural causes, this event is more frustrating – the deaths were man-made and preventable.

The U.S. Geological Survey’s National Wildlife Health Center reports wildlife authorities have collected about 7,000 dead Mallard ducks near Pierre, South Dakota – and they’re still counting. The Minneapolis Star Tribune published a gut-wrenching photo yesterday of a pond filled with dead ducks. (The South Dakota Department of Game, Fish & Parks did not respond to our request to reprint the photos here; the U.S. Fish & Wildlife Service said the photos are not in the public domain.)

Officials are attributing the deaths to aspergillosis (PDF), a respiratory disease caused by a fungus. The disease is deadly to birds. Mallards are often susceptible during bad weather when they may feed in waste grain and silage pits that aren’t properly covered. They can inhale spores when feeding on old moldy grain such as corn, which is the prime suspect in this case.

And there’s a worry the disease could spread:

The [U.S. Fish and Wildlife] Service was concerned that an eagle die-off might also occur in the area because the big birds — hundreds had been wintering there — were seen feasting on the dead ducks.

“The sad part of this is that it is totally preventable with good farm management,” Dr. Doug Inkley told me. He’s the National Wildlife Federation’s senior scientist. “It’s ironic that this ongoing die-off caused by mankind utterly pales in comparison to what the future holds for Mallards and the many other waterfowl species that depend upon America’s prairie pothole region for breeding.

America’s waterfowl are more vulnerable thanks to a 2001 Supreme Court decision weakening the Clean Water Act. A narrow reading of the Court’s decision meant that “isolated, non-navigable, intrastate waters” like prairie potholes – depressions that often fill with snowmelt and water in the spring – would no longer be afforded Clean Water Act protection just because they are used by migratory birds.

This puts prairie pothole wetlands at immediate risk to plowing and development. And that’s not the only threat they face. “With global warming, hundreds of thousands of prairie potholes are expected to either dry up completely, or dry up so quickly in the spring that they will no longer provide the essential habitat for millions of waterfowl to breed,” says Dr. Inkley.

What can you ask your member of Congress to do to protect these birds?

Enact legislation to restore protections

Develop a new energy future, one that relies on clean energy and breaks our dependence on polluting coal & oil, to curb the carbon pollution that is driving global warming

While bird die-offs like this are tragic, it’s reassuring to know we can protect these species from much greater, long-term threats – but only if we act now.