The River

Among the most startling sights in this desert country may be the teethmarks of beaver on cottonwood or willow trees along the Rio Grande. But don't look for beaver lodges. The beaver in the Big Bend live in bank burrows. The river is an oasis for species not adapted to the aridity of desert life, and so it adds to the park's rich biological complexity.

The garfish and some turtles which swim in the river are living fossils that help describe its former life as a lush savannah and swamp some 50 million years ago. Their ancestors then swam in company with crocodiles and hippopotamus-like creatures.

Near the river lives an extreme and ancient example of geographic isolation—the Big Bend mosquitofish (Gambusia gaigei). Not only is this creature's range restricted to the park, but it is also restricted to a single pond. The fish was first identified in 1928 in Boquillas spring, which led scientists to believe it extinct when the spring dried up. Then, in 1954 the species was rediscovered near Rio Grande Village. With the help of conservationists and biologists, the fish have survived, even though two males and one female were the only living representatives of the species at one point. The Big Bend mosquitofish gives birth to live offspring and has been around as a species since the time of the mastodons. They feed largely on mosquito larvae.

The Rio Grande riverside is home a most unusual amphibian—Couch's spadefoot toad. The toad evades drought by burrowing with some specially adapted, shovel-like feet. When rains come, the toads move to the nearest puddle and mate. Their eggs hatch six times faster than those of garden toads and the tadpoles quadruple their birth weight by the second evening of life. With luck some mature before the puddle evaporates, when they can dig in to await another wet spell.

The Desert

The harsh climate of the Chihuahua desert demands serious concessions from those who call it home.Two desert creatures found in Big Bend, the kangaroo rat and the roadrunner, exemplify these adaptations to the arid climate. Neither drinks water. The roadrunner gets its moisture largely from its omnivorous diet, which includes lizards and small rattlesnakes. The kangaroo rat metabolizes both energy and moisture from seeds that contain less than 4 percent water. It has no sweat glands and cools itself mostly by breathing. Its nasal passages condense breath moisture for retention. Its kidneys, among the most efficient in the animal world, excrete uric wastes as a concentrated paste rather than as a liquid, saving further previous water.

Many animals survive life in the desert by coming out only at night. Most snakes do this because summer daytime temperatures on the desert floor would kill them within minutes. Some of the park's lizards, though, brave the daytime heat to do their hunting. Most often seen is the western whiptail. The greenish collared lizard may be seen racing along on his hind legs like a miniature dinosaur. Lizards are about the biggest ground dwellers you scare up on a noonday walk, unless you happen upon a lizard-eater like the big, pink western coachwhip snake.

Other animals have their own unique ways of beating the daytime heat. Some insects fly straight up in the air a short distance, where it is significantly cooler. There is a beetle that seems to walk around and raise itself up on stilts periodically. It, too, is just achieving a critical distance from the desert floor's killing heat.

The Mountains

The cooler, greener Chisos mountains act as something of an oasis in this punishing desert. Wildlife thrives here that could not withstand the harsh aridity. The Sierra del Carmen whitetail deer are one graphic example. These mountain-dwelling animals seem to be"left over" from an earlier geologic time. The deer live in the United States only in the Chisos Mountains and other nearby ranges. In the entire world, they live only here and across the Rio Grande, similarly isolated in the Sierra del Carmen, and possibly in a few other isolated spots in Mexico. Whitetail deer are not adapted to desert conditions. They may have had a much wider range in this region during the Ice Age, when the climate was cooler in this area. As the climate warmed, cooler conditions prevailed in the Chisos—and Sierra del Carmen—Mountains because of their elevations. Today, the fate of this smaller whitetail deer can be monitored by watching the desert mule deer gradually encroach on the mountain foothills. The mule deer, adapted to desert life, appear to be usurping some whitetail range.

The Chisos Mountains are also home to two powerful and potentially dangerous animals—the mountain lion and the black bear. The regal cat, locally called a panther, has given its name to the lion's share of park places, such as Panther Pass and Panther Junction. Most park sightings of mountain lions take place at Panther Pass, usually in May or June.

In an extraordinary turn of events, the black bear began recolonizing the Big Bend area in the mid 1980s. Visitors to the area around the turn of the century (1900) reported seeing numerous black bears, but by the time the park was established in 1944, hunting and trapping had virtually decimated the region's resident population. Surprisingly, in the 1980s, park visitors began reporting black bear sightings and the numbers have just increased since then. In 1996, 572 sightings occurred. Black bears thrive in the juniper, piqon pine, madrone, oak, and persimmon trees of the Chisos Mountains where they find shade and shelter. They eat pine nuts, madrone berries, and acorns, as well as prickly pear fruit, sotol, and yucca. Mountain pools provide drinking water much of the year.

These Chisos mountain plants—specifically the blooming century plants—also provide sustenance to a rare species of mammal—the Mexican longnose bat. The bats spend most of the year in Mexico, but can be seen in the park in June or July when they feed on the nectar of these flowering plants.

Birding

More than 400 species of birds have been seen in this birders' paradise, including one—the Colima warbler—that is found nowhere else in the United States. The park lies right on the flyway for birds winging north out of Mexico and, indeed, almost three-fourths of the species recorded in the park fly right on through. During the spring migration northbound birds confront the northwest-southeast trending Sierra del Carmen mountains. Instead of flying over them, most birds keep to the west and are funneled right into the park. For the return trip in fall, however, the Sierra del Carmen have the opposite effect. Many southbound birds peel off east at Persimmon Gap. The fall migration is smaller and brings more lowland than mountain species.

The springtime bursts of birdsong are inspired by the drive to claim territory, as some 100 species nest within the park. Many of these breeding birds will abandon the lowlands as soon as their young are big enough, moving to the mountains to beat the heat. Rio Grande Village, for example, is at its low ebb for birdlife in July, and in the Chisos Basin you will find yourself identifying lowland birds left and right! But all in all, Rio Grande Village, with its ponds, cottonwood groves, rich riverbottoms, heavy brushlands, and neighboring desert, is the best year-round birding site in the park. In the springtime it offers an unbelievable display of species.

The Chisos Basin is the second best overall birding site, providing a long parade of mountain birds throughout the year, as well as lowland birds. The Basin is one of three spots for the annual Christmas Bird Count, along with Rio Grande Village and the Castolon-Santa Elena Canyon area. Over a five-year period, 147 species have been counted at these locations at Christmas time.

By the Rio Grande, you find summer tanagers, painted buntings, vermilion flycatchers, and cardinals serving as accent colors to the background greens of floodplain foliage. On the river's gravel and sandbars and on its cliffbanks are other creatures you would not expect to find in the Chihuahuan Desert. The sandpiper and killdeer bob and sprint on the sandbars, and the cliff swallow flies up to its adobe nest fashioned of river mud.

The Colima warbler is probably the park's most famous bird, because in all the United States it nests only here in the Chisos Mountains. It arrives in April from southwest Mexico and leaves in mid-September. The Big Bend has also remained one of the few successful breeding grounds of the peregrine falcon, a species that suffered much from pesticides. You are most likely to see peregrines during their spring migration, but nesting pairs have been sighted at Santa Elena, Mariscal, and Boquillas canyons and in the Chisos Mountains. These predatory birds prefer to nest in a scrape on a high cliff ledge. This falcon, about the size of a crow, is slaty backed and barred below, with a pair of black "mustaches" on the face. In its magnificent dive, the peregrine is one of the fastest moving animals on Earth.

For advice on good birding spots at any time of the year, or on where to find specific birds, ask a ranger or at park headquarters.

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