“Performance is definitely affected by the lack of insurance, combined with the high risk factor and the lack of training and equipment,” said Rohit Singh, the lead author of the World Wildlife Fund studies. “How can we expect rangers to deliver if they do not have these basic things?”

When rangers are well taken care of and receive appropriate training, poaching rates tend to drop, Mr. Singh and Mr. Willmore said.

Lewa Wildlife Conservancy, a wildlife sanctuary in Kenya, for example, was losing unprecedented numbers of rhinoceroses when it overhauled its operations in 2014. To turn things around, the conservancy invested in specialized training, brought in a helicopter, installed a new communications system and strengthened relationships with local communities.

Since then, Lewa has not lost a single rhino.

“There was a time when rhinos were poached here so often that we were becoming scared, but we’ve tried our best and we’ve stopped it,” said Francis Kobia Chokera, 44, a ranger at Lewa. “We had security before, but not like it is now. It’s very, very tight.”

Mr. Chokera’s job is still demanding: He patrols on foot for 12 hours a day, and like 47 percent of the rangers interviewed by the wildlife fund, he sees his family fewer than five days per month. But he has insurance, earns around $3,600 a year — more than two times the average income in Kenya — and receives overtime, free housing and a pension.

“By good luck, I was given the chance to work here,” he said. “I’ve always loved animals.”

Timothy Tear, executive director for the Wildlife Conservation Society’s Africa program, said that success stories like Lewa’s are “where hope is found.” He noted that the conservancy’s considerable investment in security and ranger training — $1 million a year — has been integral to its success.

“If you do the simple math of dollars spent to acres protected, you will find Lewa at the top of the investment-per-acre gradient,” Dr. Tear said.