The last 50 wild donkeys on Hawaii's Big Island will be rounded up to mark the final step in a six-year effort to get them in adoptive homes.

The donkeys are the last of more than 500 who were cast-offs from the early days of Hawaii coffee and agricultural plantations.

When drought conditions forced the donkeys into residential areas in search of water, the herd became a problem when the animals started going into roadways, tearing up golf courses and drinking out of swimming pools, said Inga Gibson, Hawaii state director for the Humane Society of the United States.

The Society and Big Island residents are starting work on Friday to prepare the donkeys for adoption. All donkeys will get check-ups from a veterinarian before they're hauled off to their new homes.

"One of our first complaints was the donkeys were actually coming into the school yard," said Gibson, adding that some Big Island residents were so fed up with the donkeys that they threatened to kill them, while others wanted to use their meat to make jerky.

The herd went entirely unmanaged for nearly 40 years because they weren't considered game or endangered animals, said Gibson. It's believed the donkeys were moved to Waikaloa from Kona in the 1970s when development grew in the area, Gibson said.

The Humane Society stepped in six years ago after getting calls from concerned residents. Since then, they've spent about $200,000 to get more than 450 donkeys in homes, including 120 who were flown to California in 2011 and found homes through Eagle-Eye Sanctuary Foundation and Peaceful Valley Donkey Rescue, said Gibson.

"It was a daunting situation initially, like what are we going to do with 500 feral donkeys?" said Gibson. "It was really just an amazing community effort, and we didn't receive any kind of government support or funding."

Waimea veterinarian Brady Bergin said a local rancher is currently working to round up the last of the donkeys so they can be prepared for adoption. The donkeys are being lured into a corral using a water trough, he said. Once the donkeys are in the corral, they'll be hauled to Bergin's vet clinic.

Before adoption, the donkeys must have a clean bill of health and the males must be castrated, which is an easier and less invasive process than spaying the females, he said.

Gibson said about 70 to 80 percent of the remaining 50 donkeys have interested homes. Hopeful donkey adopters must go through a strict screening process to make sure they have enough land and know how to care for the animals, which have never had human contact, said Gibson. It can take anywhere from weeks to months to train donkeys to lead from a halter and interact with humans, Gibson said.

Donkeys are very social animals, so they must be adopted in pairs or have another animal to keep them company at their new home, she said.

"The adoption clause is no lone donkey," said Gibson. "They have to have a friend."