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Wildlife and Habitat

RioGrande_512x219Known as the lower Rio Grande Valley, the lower four counties of Texas contain a documented 1,200 plants, 300 butterflies, and approximately 700 vertebrates, of which at least 520 are birds. It is to protect this important biodiversity that the Lower Rio Grande Valley National Wildlife Refuge was established. 

Thousands of years of geographic change and evolutionary adaptation have resulted in the creation of numerous and distinct plant and animal communities in the four most southern counties of Texas. Many of these are found in and protected by the Lower Rio Grande Valley National Wildlife Refuge.

The Ramaderos biotic community sits at the western edge of the refuge. This arid landscape is cut by deep arroyos and small tributaries that extend for miles from the Rio Grande. Wildlife travels unimpeded down the humid corridors of lush riparian vegetation, particularly during times of drought and extreme heat. The biota of these natural drainages is a result of higher moisture and deeper soils. A tree typically foraged upon by white-tailed deer and cattle, the seemingly unobtrusive guayacan, has a root system that plant ecologists speculate may endure for about 1,000 years.

At the eastern edge of the refuge, impaled insects and small rodents adorn the blades of large, 100-year-old yuccas called Spanish daggers, compliments of a migratory bird, the loggerhead shrike. The irony of this macabre scene is not lost on the people who visit Palmito Ranch, site of the last land battle of the Civil War and a refuge tract that falls within the Clay Loma/Wind Tidal Flats. This biotic community is interspersed with saline flats, marshes, shallow bays, and unique dunes of wind-blown clay known as lomas. Following the last few miles of the Rio Grande, this refuge tract links coastal and river corridors and is staging ground for the endangered peregrine falcon. It is also habitat for 17 other federally listed threatened and endangered species, including the Kemp’s ridley sea turtle.

A species of great concern to the U.S. Fish and Wildlife Service is the ocelot, an endangered cat whose numbers have dwindled to fewer than 50 in the United States. The Mid-Delta Thorn Forest, a biotic community that once covered much of the delta, is a hunting ground for this nocturnal species. Texas ebony, Granjeno and colima are but a few of the trees and shrubs that house an array of small mammals and birds, prey for the ocelot. Typified in remnant strips along fence rows, canals and ditch banks, the diminished thorn forest habitat forces the solitary ocelot to cross open fields and risk the dangers of vehicular traffic and predators.

Before dams and water control structures significantly reduced the flow of the Rio Grande, periodic floods cut shifting channels into the delta creating crescent-shaped oxbows, referred to in the Valley as “resacas.” Resacas, complemented by dense bottomland hardwood forest, are characteristic of the Mid-Valley Riparian Woodlands biotic community. This habitat is particularly favored by birds such as chachalacas and green jays, as well as another endangered and elusive cat, the jaguarundi. Draping Spanish moss and another epiphytic bromeliad, the rare Bailey’s ball moss, cling to cedar elm and Texas ebony. Found throughout the delta, brush-bordered resacas typical of this community attract many of the neotropical migrants and waterfowl that funnel through the Valley on their way to and from Central and South America.

On the edge of the riparian woodlands is a unique and severely diminished biotic community of sabal palms. Originally spanning more than 40,000 acres, the remaining palms are restricted to about 50 acres. They comprise one of the few strongholds for one of the rarest snakes in the U.S., the speckled racer. The southern yellow bat, a rare, year-round resident, roosts within the fronds of the remaining sabal palms that grow along the southernmost bend of the Rio Grande. The more than 900 species of beetles found within the small grove represents only a fraction of the insect community that aids plant pollination and other essential ecological functions.

The Woodland Potholes and Basins ecosystem contains numerous freshwater playa lakes and three hyper-saline lakes. Deep ruts, remnant tracks of oxcarts used by Spanish colonists to haul mined salt, can still be seen at the 530 acre salt lake, La Sal del Rey or “the King’s salt.” Black-necked stilts, black skimmers, and least and gull-billed terns can be found nesting along the shorelines of the salt lakes. The salty waters support brine shrimp and a few species of salt-tolerant water insects. Set in a low woodlands of honey mesquite, prickly pear, and lote bush, the freshwater potholes and playa lakes serve as favorite roosting and feeding areas for migrating geese, waterfowl, shorebirds, and sandhill cranes. Vegetated corridors will eventually connect this tract to the river.
 
Last Updated: Jun 11, 2012
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