The Chisos Basin, high in the mountains, is the biological island. Black bear and mountain lion both live here, having recolonised naturally, and the Colima warbler — found nowhere else in the United States — breeds up the Pinnacles and Boot Canyon trails from April to September. It is a genuine hike to reach them.

Rio Grande Village and the river corridor hold the water-dependent species. The nature trail there at dawn is the park's best general birding, with vermilion flycatchers, javelina coming to drink, and beaver in the river — an unexpected species in a desert.

The open desert along the roads and at Dugout Wells produces roadrunner, jackrabbit, kit fox at night, and the reptiles the park is quietly famous for. Drive slowly after dark and you will find far more than by day.

Santa Elena Canyon, where the river cuts a 460-metre slot through the limestone, is the landscape set piece, best at the end of the day when light reaches into the gorge.

Spring, roughly March to May, is the best all-round season: migrant birds, flowering ocotillo and cactus, and tolerable temperatures. Summer is dangerously hot on the desert floor. Winter is quiet, clear and excellent in the Chisos.

Practicalities

Big Bend is genuinely remote — the nearest airports are hours away and services inside the park are limited, so arrive with fuel, water and supplies. The park is an International Dark Sky Park and among the least light-polluted places in the lower 48; the Milky Way here is a reason to visit in its own right. Carry far more water than feels necessary, particularly for any hike below the mountains.