This time of year, the temperature routinely reaches 104 degrees in northern Botswana. The grasses recede, forcing herds of wildebeest to walk farther and farther from their only water source to graze. Humidity falls to about 10 to 15 percent.

“It’s not quite Death Valley, but it’s not quite far-off it,” said Alan Wilson, a biologist whose research examined how the wildebeest cope with such an inhospitable environment. “They’re on a physiological knife edge in terms of: How do they continue to survive?”

His research showed that these cow-like animals, also called gnus, have remarkable adaptations, enabling them to walk up to 50 miles over five days without drinking water. They can do this because their muscles work incredibly efficiently — far more than their body size would suggest.

“I don’t think we’d get to 50 miles,” Dr. Wilson said, referring to humans.

His study, published Wednesday in the journal Nature, showed that this efficiency means wildebeest don’t have to sweat or pant as much to release heat, even when they’re running in heat higher than their body temperature.