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What happens to wildlife when wetlands go dry?

(CBS News) MARKHAM, Texas -- The wetlands in southeast Texas provide sanctuary for nearly two million migrating birds each winter. But the drought is drying up their seasonal home.

Todd Steele
Todd Steele
CBS News

"We're seeing in our lifetime -- probably in a five-year period -- the birds are just disappearing on us," says Todd Steele, who runs a 20,000-acre hunting preserve where ducks and geese fatten up and rest before they fly back to the northern part of the U.S. and Canada.

"Whether they are coming down in the winter time to spend the winter, or they are trying to go back to the spring nesting grounds, they need habitat all along the way," he says. "What's happening -- we are losing a tremendous amount of our habitat, and these birds are getting stressed as a result of it."

The driest areas of the country are now along what's known as the Central Flyway, a key migration route for birds moving north and south.

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"The most insidious part about something like a drought is it covers such a large area," says Denis Dean, who studies wildlife environments at the University of Texas at Dallas. "And then it becomes not just a single wetland that is taken out of the picture, it degrades the quality of wetlands for a long, long portion of the migratory route."

Denis Dean
Denis Dean
CBS News

In past droughts, many birds found food and protection in irrigated rice farms. But water flow to many Texas farms has been cut to protect supplies for the state's growing towns.

"They reach a tipping point where they no longer are able to continue the migration, and you get these mass die-offs," Dean says. "I wouldn't say we are there, because clearly we haven't seen the mass die-offs, but I think we're getting close in many cases."

The birds will not find much better conditions when they return to the northern plains. Forecasters predict drought conditions there will persist into the summer.