Continental Divide: Wildlife, People, and the Border Wall

Rio Grande

In the Lower Rio Grande Valley, late summer dew glistens on the quivering threads of a spider web draped upon the bough of a honey mesquite. On a nearby branch, a malachite butterfly dries the morning mist off its pale green wings while a buff-bellied hummingbird pauses momentarily to clean his shimmering iridescent feathers, then zooms away. And all the while, the cries of plain chachalacas, the melody of the altamira oriole, and the chatter of dozens of other bird voices fills the air. There is no morning quiet under the riparian canopy. A sudden bright burst of colors explodes from the shade of an ebony tree—a Cooper’s hawk on the hunt has spooked a hooded oriole and long-billed thrasher. They find safety behind a veil of Spanish moss at river’s edge, and the Rio runs past, ever hurrying to the Gulf. Such is a day in the life of the South Texas wildlands. All along the Lower Rio Grande Valley, this enchanted scene has repeated itself for 100,000 years. This ribbon of native forest and scrub sits quite nearly at the midpoint between the tropics—which officially begin about 300 miles south—and the temperate zone, which starts about the same distance to the north. Sitting in the transition zone between these two distinct climates, the Lower Rio Grande Valley contains hundreds of species of plants and animals that do not exist elsewhere RIO GRANDE 1 0 4 in the United States or Mexico, and in some cases, the whole of the wild world. Like the rest of the borderlands, the Lower Rio Grande Valley sits at the confluence of several distinct natural communities . Here the Chihuahuan Desert meets the Gulf Coast, the Great Plains, and the tropics, at almost seven degrees latitude south of where the border begins in San Diego and Tijuana. This difference in latitude and a vastly different topography ensure that this borderlands region is defined by different rainfall and temperature patterns and is home to yet another unique community of wild species. The Valley contains a collection of plants and animals so diverse, its classification can be confusing even to scientists. Trees can appear as shrubs in this transitional zone; it is a compromise habitat—offering just enough of the conditions of both the tropics and temperate regions to be hospitable to many species from both of the vastly different ecological zones. Species like the northerly American elm and the tropical Mexican olive can live in the Valley, but they grow relatively small here due to the undependable moisture and altered temperature extremes. Similarly, desert trees, like mesquite, grow much taller in the milder and wetter Valley than they do in the more arid regions further west and south. And as it goes for flora, so it is for fauna. Ocelots stalk the thick brushlands of South Texas, one of only two places in the United States where these small cats still roam. About twice the size of the average house cat, with fur like a jaguar, this wild feline is at home in the tropics as well as in the warm subtropical habitats of the far southern United States and northern Mexico. Existing on rodents and rabbits and sometimes birds and lizards, ocelots travel areas thick with grasses or brush to keep out of sight. Somewhere in its roamings, the ocelot may encounter another reclusive feline shadow in the thick vegetation of the Rio Grande Valley: the jaguarundi. This small dark cat possesses a stealth that makes it an extremely rare sight for human eyes; catching a r i o G r a n d e | 1 0 5 glimpse of this shy cat in the Valley would be akin to winning the wildlife-watching lottery. Where the Rio Grande empties into the Gulf of Mexico at Boca Chica, endangered Kemp’s Ridley, loggerhead, and green sea turtles dig nests in beaches, tucking their eggs away beneath a warm blanSide channel of the Rio Grande in the Santa Ana National Wildlife Refuge in McAllen. 1 0 6 A long-billed thrasher in the Lower Rio Grande Valley. The species is endemic to northeastern Mexico and South Texas. r i o G r a n d e | 1 0 7 ket of sand. Above them, shorebirds forage for invertebrates tossed onto the beach by the incessant waters of the Gulf. These...