Aransas National Wildlife Refuge - Texas

Whooping cranes, the largest of the North American cranes, descend on southeastern Texas tired and eager to feast on the blue crabs that populate the waters of Aransas National Wildlife Refuge. Once nearly extinct, these big birds fought their way back from a low of 15 in 1941 to a total of 470 worldwide. Two hundred of these whooping cranes, the only wild, self-sustaining population, winter at Aransas.

While whooping cranes are the most renowned resident of Aransas, the refuge is alive with critters that thrive in its brackish tidal marshes, freshwater ponds, grasslands and oak woodlands. Five sea turtle species, all listed as threatened or endangered, paddle the refuge's waters or nest on its beach. More than 400 species of birds are on record here, including colorful clouds of migratory songbirds that settle into the forest cover after their long spring migration across the Gulf of Mexico.

The Threat

The characteristics of the Aransas landscape that make it a haven for the whooping crane, sea turtle and many other species also make it vulnerable to the effects of global warming. The refuge is composed mostly of low-lying coastal land with shallow estuarine marshes that barely rise above sea level. The predicted rise in sea level would flood coastal marshes and other low-lying lands, erode beaches, and possibly increase the salinity of rivers and groundwater. The Environmental Protection Agency estimates that nationwide a two-foot rise could eliminate 17 percent to 43 percent of wetlands in the United States.

For sea turtles, this alteration of coastal nesting habitat may be beyond their already stressed powers of adaptation. Like many other species, they depend on sea temperatures and levels remaining relatively constant. Similarly, the drowning of wetlands, especially if other suitable habitat is not available, could devastate wetland-dependent birds such as the whooping crane.

Whooping cranes need shallow waters. If sea levels rise as expected, most of their current habitat in the refuge would be too deep. Development, including roads, will prevent higher ground from becoming new habitat. Additionally, warming threatens to alter rainfall patterns. Droughts in the cranes' nesting grounds in Canada are of particular concern because breeding success is often tied to adequate rainfall. In dry years, whooping crane nests generally fail.