Among the most startling sights in this desert country may be the tooth marks of beaver on cottonwood or willow trees along the river. 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 biological diversity. The river floodplain provides good areas for birdwatchers.
Some birders maintain that the birds in the floodplain are more colorful than elsewhere.
Here you find summer tanagers, painted buntings, vermilion flycatchers and cardinals serving as accent colors to the background greens of floodplain foliage. This ribbon-like floodplain verdancy, seen from a distance, appears as a green belt in the desert. It is a phenomenon seen elsewhere in the park along arroyos, or washes. Undoubtedly you will find birds and other animals making ample use of this interruption of more arid desert vegetation. On the river's gravel and sandbars and on its cliffbanks are other creatures you would not expect to find in the Chihuahuan Desert.