The blue of the sky contrasts with the gold of the landscape below, as pilot Cade Woodward dips and circles his plane above the Marfa Plateau. It's a treat for any West Texan – a bird's-eye view of where the grasslands meet the Davis Mountains – but this is not a recreational flight.

On a spring outing, Woodward and biologist Nan Nourn are tracking pronghorn. It's part of the effort – now five years old – to prop up a struggling pronghorn population in these Trans-Pecos grasslands.

The Trans-Pecos once had the state's largest pronghorn herds. But by 2010, scientists had confirmed an alarming decline – the population fell from 17,000 in the mid-80s to just 2,200. Herds north o...