The armed men guarding the last male northern white rhino on Earth say they're overwhelmed by the online support they're getting, after photos of them escorting the animal went viral.

The photos show the armed "Rhino Rangers" standing guard around a rhino in the Ol Pejeta wildlife sanctuary in Kenya. The images were captured several months ago, but recently went viral on Twitter, touching off a surge in donations to the Rhino Rangers' GoFundMe campaign. A post on the GoFundMe page early Tuesday says more than $4,600 has been donated since Sunday.

"We're blown away by all your donations and messages of support!" the post said.

The Rhino Rangers are the last line of defence for 105 black rhinos, 23 white rhinos and three of the last five remaining northern white rhinos in existence at the Ol Pejeta sanctuary. The rhinos are targeted by poachers, who kill the animals and steal their horns for sale on the Asian black market.

The Rhino Rangers say two rhinos have been killed at their sanctuary in the last 18 months, but the poachers did not get away with the horn in either case. Neither rhino was a northern white rhino.

The three northern white rhinos at the sanctuary are some of the rarest creatures on Earth.

They arrived at the sanctuary in 2009, as a group of four from a zoo in the Czech Republic, in hopes they would breed and keep the race going. There were two males and two females in the group, but one male died last October.

The last male, named Sudan, is now 40 years old and nearing the end of its expected lifespan.

Kelvin Alie, a program director for the International Fund for Animal Welfare, said demand on the market for rhino horn products is on the rise.

“It’s really sad to see that this particular rhino has to be put on 24-hour armed watch for its survival,” Alie said in an interview on CTV’s News Channel on Tuesday.

Animal welfare organizations are taking a “holistic approach,” Alie said, to address the issue by trying to stop poaching and demand for animal products, and by supporting wildlife law enforcement.”

“That’s the rangers, the people on the frontline,” Alie said. “We also work with customs and border officials to ensure that we address the issue of trafficking and the movement of products.”

There are some positive movements however, including captive breeding efforts in southern Africa and other countries that “hopefully will bring the species back from the brink of extinction.”

Population estimates counted about 2,000 northern white rhinos in the 1960s, but those numbers were decimated by unchecked hunting in the decades that followed. The World Wildlife Foundation says there were between 17 to 22 individuals alive at a protected park in July 2004, but those animals were wiped out in short order. By 2009, the only remaining northern white rhinos were those held in zoos.

In addition to the three rhinos now at Ol Pejeta, one northern white rhino remains at the Dvur Kralove Zoo in Labem, Czech Republic. The other is at the San Diego Zoo in the United States.