The world's last remaining natural flock of endangered whooping cranes, which suffered a record number of deaths last year, will probably see another die-off because of scarce food supplies at its Texas nesting grounds this winter, wildlife managers said.
The flock lost 23 birds in the 2008-2009 winter season, in part because its main source of sustenance, the blue crab, all but vanished from drought-parched southern Texas. The rains eventually came, but they were too late to produce healthy amounts of blue crabs for this winter.
“We're looking at a pretty slender year, prey-wise, and it's going to make the cranes work harder to get food,” said Allan Strand, field supervisor for the U.S. Fish and Wildlife Service in South Texas. “I feel that we're probably going to have a die-off. It's conceivable that we could have a significant die-off.”
The whooping crane, the tallest bird in North America at about 5 feet, was nearly extinct in 1941 before making a steady comeback. There are three flocks now, but the one that travels 2,400 miles each fall from Canada to the Texas Gulf Coast is the only one that migrates without human help.
According to the most recent aerial survey, there are an estimated 263 birds in the Texas flock. The survey, conducted last week, found that one chick has already died and another was missing.
It's normal for one crane to die in the average November-to-March winter season, and last year's 23 deaths were the most since 1938 when the wildlife service began tracking cranes at the Aransas National Wildlife Refuge near Corpus Christi.
Also in last week's survey, Tom Stehn, the wildlife service's whooping crane coordinator, noted some birds were already leaving the marshlands to search for food elsewhere. An extended hunt for food would burn more important energy that the cranes need to survive the lean winter months, he said.
The crabs are loaded with fat and calories, and an adult whooping crane can eat up to 80 a day. But when their crab count is down, the cranes can end up in bad shape, particularly after the draining migration from Canada, Strand said. Last year the flock's hatch was down about one-third, and “that's a direct correlation to the birds' health when they get back,” he said.
The cranes face other challenges. They are losing habitat to housing developments that draw even more water out of their nesting grounds along the Guadalupe and San Antonio rivers.
Last month, a conservation group filed paperwork to sue state regulators, alleging they allowed too much water to be taken from the rivers during the crane wintering season. That overuse increased the salinity of inland waters, hurting the birds' water and food supplies, the group said.
The wildlife refuge has requested permission to put out calorie-rich “crane chow,” the same kind of food the birds eat in zoos. Even if they are allowed to do that, there is no guarantee of success.
The cranes generally nest in pairs or as a couple with one juvenile spread out along a 30-mile coastline. Even if the food distributors correctly target the birds, there is no guarantee they will eat the chow.
Some experts disagree with supplemental feeding, but Strand said it might be necessary.
“The cranes are not a viable population,” he said Tuesday. “They can't support themselves. I hate to think if we don't do it and we lose another 30 or 40 cranes this year, I don't know how we're going to explain it.”
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