Migratory bird populations affected by hurricanes






By B. Blair Dedrick

Washington - On the morning after Hurricane Katrina, Judith Toups woke up to see more than 30 ruby-throated hummingbirds in her Gulf Port, Miss., backyard. The hummingbirds were looking for food before their long migration to the tropics. What they found instead were trees stripped of their leaves, flowerless plants and few insects.

"The storm knocked out all the flowers," said Toups, a 75-year-old founding member of the Mississippi Coast chapter of the Audubon Society. "The food supply was pretty low." Toups was not alone in her concern about the bird population after Hurricanes Katrina and Rita. While the exact impact on the migrants is unknown, experts say migrating bird populations will feel the effects both this fall and into next spring.

Trans-Gulf birds, or birds that migrate across the Gulf of Mexico, have at least a 550-mile, open-water flight from the Mississippi, Alabama and Louisiana Gulf coastal regions to their Central and South American winter homes. Other migrants take an overland route via Texas and Mexico. Peak migrating season is from September through December. In either case, the Gulf Coast is a major energy-building stopover for the birds, who feed heavily before the long flight. The ruby-throated hummingbird, for instance, doubles its weight before flying to wintering grounds in Central America.

"The long-lasting and extensive impact of the hurricanes is on the habitat that the birds use as stopovers," said Sidney Gauthreaux, a professor of biology at Clemson University. "That effect can go over this migration season and into the spring migration." Gauthreaux uses Doppler radar, including that of the National Weather Service, and thermal heat imaging to survey migrant birds. While conditions on the Gulf Coast have prevented him from using his portable gear to survey this season, he said he is concerned about the effect the hurricane-ravaged habitat will have on the birds.

Normally, nearly 80 percent of migrating birds die during migration, Gauthreaux said. That number can increase when winds and floodwaters, or any other extreme factors, leave little to eat for the herbivorous insects, like caterpillars, that most migrants eat. Berry-eating birds are also in trouble, as the influx of salt water has probably killed bushes that survived the actual hurricanes.

"It's a risky business," Gauthreaux said. "You don't know if the habitat will be the way it was last year." Bruce Reid is the deputy state director of Audubon Mississippi and head of the Vicksburg, Miss., Bird Conservation Office. In addition to the trans-Gulf migrants, Reid is concerned about migrant birds from Canada that over-winter on the Gulf Coast.

"Frankly, one would imagine that a lot perished," he said. "And the only ones who are left will have a harder time." Watching out her windows, Toups said the number and variety of migrant birds was extremely low at her house, about a mile from the beach where some of the strongest winds and highest storm surges were recorded. “Normally, we get almost anything, especially the insect eaters and wood-warblers," she said. "They are just plain not here."

Scott Sillet of the Smithsonian Institution's Migratory Bird Center said that was not necessarily unusual under the circumstances. "Migrants move along broad areas of the Gulf Coast," he said, explaining that the birds fly with the prevailing winds.

Many birds will not stop if there is no habitat, Sillett said. The coastal woodlands are a very important refueling stop for the migratory birds, and most of those woodlands were destroyed. Though the situation is not ideal, the area is slowly recovering, said Toups, who has written a book and several articles about migrating coastal birds.

On the Mississippi coast, she has seen pear trees and other flowering plants beginning to bloom as if in spring, and the hummingbirds are beginning to thin out as they continue on their fall migration. "Every day things get a little bit better," she said. "That's why I'm paying attention. I want to see how long it takes backyard birds to recover and the migrant birds to come back."

Source: Scripps Howard Foundation