Water is of paramount importance in the desert country of Big Bend National Park. Plants adapt to the hot, dry terrain by growing small leaves. Waxy coatings limit transpiration of water by plants. Cacti have done away with leaves altogether. Plants such as the ocotillo only produce leaves after sufficient rainfall.
Animals also adapt to the arid conditions.
Most come out to feed and hunt only at night during cooler temperatures. Because water is scarce at Big Bend, springs and water holes are particularly valuable. Permanent creeks are rare. One major exception, the Rio Grande, creates a long, narrow oasis, a ribbon of green, along the southern boundary of the park. The river and springs are vital to the park's wildlife.