Big Bend National Park is an 800,000-acre wilderness in West Texas, containing the largest protected area of the Chihuahuan Desert in the United States. Its biodiversity stems from a unique convergence of three distinct ecological zones: the arid Chihuahuan Desert lowlands, the cooler “sky island” habitats of the Chisos Mountains, and the Rio Grande corridor along the border with Mexico. This dramatic variation in elevation, from 1,800 feet along the river to nearly 7,800 feet in the mountains, creates diverse microclimates and habitats. The park is a refuge for a remarkable number of species, including over 450 types of birds, 75 species of mammals, and 56 species of reptiles.
The Iconic Large Mammals
Visitors often seek out the park’s large mammals, which include a successful population of Black Bears. These bears were absent from the region for decades but began recolonization in the late 1980s, migrating across the Rio Grande from Mexico. They are most commonly found in the forested slopes of the Chisos Mountains, where they forage on acorns, berries, and sotol plants.
Mountain Lions, also known as cougars or pumas, are the apex predators of the Big Bend ecosystem. They are elusive and solitary animals, but their presence is noted throughout the park, with over 150 sightings reported annually. Their diet consists mainly of deer, though they also hunt Javelinas and rabbits, helping control herbivore populations.
The park is home to two species of deer that occupy different niches. The Desert Mule Deer are found in the open, rugged canyons and hillsides of the lower desert. Conversely, the smaller Carmen Mountains White-tailed Deer prefers the dense vegetation of the Chisos Mountains above 4,000 feet. Collared Peccaries, or Javelinas, are also frequently seen traveling in groups called squadrons as they forage for roots and cacti. Though they resemble wild pigs, Javelinas are a separate species, distinguished by their musky scent gland.
Reptiles and Amphibians of the Desert
The Chihuahuan Desert environment makes Big Bend a haven for reptiles, with 56 species documented. Lizards are abundant and often observed during the day, with 22 species present. The Greater Earless Lizard is a notable example, lacking external ear openings and displaying a high tolerance for heat. Males exhibit a striking pink and green coloration during the breeding season.
Snakes are also well-represented, with 31 species, most of which are non-venomous. Four species of rattlesnakes are present, including the widespread Western Diamondback Rattlesnake and the Rock Rattlesnake. The Rock Rattlesnake in the Chisos Mountains is known for a distinctive red or maroon color phase, which aids in camouflage against the local rocks.
Amphibians are adapted to the park’s unpredictable rainfall. The Couch’s Spadefoot Toad spends most of its life deep underground encased in a moist sac. When a significant summer rainstorm occurs, the toads emerge to quickly breed in temporary pools of water. They are named for a spade-like projection on their hind feet, which is used to bury themselves rapidly. This compressed life cycle allows tadpoles to mature in as little as nine days before the pools evaporate.
Avian Life of the Borderlands
Big Bend’s location on a significant migratory route and its varied habitats attract over 450 species of birds. The park is renowned among birding enthusiasts for the Colima Warbler, a small, grayish songbird. This species is found in the United States almost exclusively in the high-elevation oak-pine woodlands of the Chisos Mountains, typically above 6,000 feet. They arrive in late April to breed.
Lower elevations and the river corridor support different avian populations. The Greater Roadrunner is a familiar desert sight, known for its ability to run up to 20 miles per hour while hunting. Raptors like the Red-tailed Hawk and Golden Eagle can be seen soaring overhead, utilizing thermal updrafts. The Rio Grande corridor is an important habitat, as the permanent water and riparian vegetation create an oasis supporting a wide variety of resident and migratory species.
Safe Wildlife Viewing Guidelines
Observing the park’s wildlife responsibly requires maintaining a respectful distance at all times, generally 50 yards from large mammals like bears and Javelinas. The park strictly prohibits feeding any animal, as this causes them to lose their natural fear of humans and can lead to aggressive behavior. Food, trash, and scented items must be secured in bear-proof containers or stored inside a vehicle.
Wildlife activity is highest during the crepuscular hours, making dawn and dusk the most productive times for viewing. Locations near water sources, such as the Rio Grande Village or the Chisos Basin, attract a higher concentration of animals. When hiking, make noise to alert animals to your presence and never approach an animal. If a Mountain Lion is encountered, do not run; instead, make yourself look larger and back away slowly.