Flooding is a fact of life on the Mississippi River. Just ask anyone living in one of the small oxbow-lake communities, like the residents of Dacus Lake in Arkansas just over the Hernando DeSoto Bridge. They have to pull their mobile homes up to the farm roads near I-40 every time the river rises 20 feet or so. But there's one species living on the mighty Mississippi that doesn't have the luxury of moving their homes to dry land: the endangered interior least tern.
Interior least terns are small, white- and-gray birds with forked tails. They nest on the river's sandbars, but their nests can be washed away if the river rises too high. In the flood of 1993, nearly every sandbar in the Memphis area was covered in several feet of water. The river took thousands of chicks and eggs with it.
"River [flooding] inundates more [least tern] chicks and eggs than any type of river recreation," says John Rumancik, a fishery and wildlife biologist for the Memphis District of the U.S. Army Corps of Engineers. "A lot of times, the river will be down in June and the birds will start nesting. But if there's a whole bunch of rain in the Ohio River Valley, that affects our water level here, and it wipes them out."
Somehow enough birds survive for them to come back each year. The Corps of Engineers is in charge of surveying the population every summer. Last year, 8,000 birds were counted, the highest number recorded in this area to date. Nearly two-thirds of the interior least tern population can be found in the stretch of river between Cairo, Illinois, and Vicksburg, Mississippi. The U.S. Fish & Wildlife Service's interior least tern recovery plan only requires that 3,400 birds be present in that stretch to maintain the species.
On a local level, the birds' survival is largely due to the corps' efforts to improve their habitats. While there's not much they can do about flooding, they've helped create safe areas for the birds when water levels are normal.
Since the birds nest on sandbars rather than trees, they're an easy target for predators like coyotes, owls, foxes, and snakes. If a sandbar is attached to the river bank, it's easy for a hungry coyote to find a buffet of eggs and defenseless baby birds.
"We've been trying to increase the nesting habitat by isolating some of the sandbars on the Mississippi River," says Rumancik. "We put notches in the dikes we build to make water flow into the back chutes around these sandbars. That acts as a moat to keep predators out."
The corps also arranges work schedules in certain areas of the river so as not to disturb the birds. If a proposed work site is near a nest of terns, corps engineers are instructed to wait until the terns leave. The birds generally move once the young are hatched and mature enough to fly.
The birds can be found on most major river systems in the interior of the U.S., including the Missouri River, the Red River, and the Yellowstone River. In some areas, conservation groups actually construct sandbars for the birds to nest on, but Rumancik says that wouldn't work in Memphis. "Since the river rises up to 40 feet at times, any sand you pump out there is just going to get washed away by the high water. It wouldn't be very economical because it wouldn't be there next year," he says.
People are one of the main reasons the birds were put on the endangered list. In the late 1800s, fashionable women wore least tern feathers on their hats. Some hats would even be adorned with an entire stuffed bird. River channeling and dam building have also been major contributors to the least terns' habitat loss.
Irresponsible recreational river users can also be a threat.That's why the corps doesn't mark sandbars where the birds are known to nest. They fear people picnicking on sandbars would notice the nesting colonies and disturb the eggs. Once the eggs are moved, the mother abandons them.
"They may even mob you until you leave their colony," says Rumancik. "If you see gray-and-white birds on a sandbar, don't go walking through the colony and disturbing the eggs. Be considerate and just watch them from a distance."