Big Bend National Park, with an incredible 450 species of birds within its borders (if not all at the same time), is the best National Park for birding, easily. Like the Rio Grande Valley, it has uniquely occurring species which can be found nearly nowhere else in the United States. Some of these species are the Mexican Jay and Duck, the Gray Vireo, the Colima Warbler, and the Varied Bunting. Less unique, but still of interest, the rare Black-capped Vireo also occurs here, as does the Peregrine Falcon. The Montezuma Quail, formerly thought vanished from the area, has recently returned to the park.
Big Bend has different regions within itself, some better for different species than others. The Colima Warbler nests in the Chisos woodlands, as do the Band-tailed Pigeon, the White-throated Swift, the Acorn Woodpecker, and the Rivoli's and Blue-throated Hummingbirds, as well as more common species like the Canyon Wren. The Big Bend grasslands are home to some common species as well, but also that Gray Vireo and Varied Bunting, and the Crissal Thrasher nests here. At the Rio Grande itself are the Yellowthroat, the Ground Dove, and the Elf Owl, as well as Brown-headed Cowbirds and Cardinals, for Big Bend is truly diverse.