They are the ancestors of Hawaii’s plantation work force, donkeys brought to the Big Island to work in coffee fields and then cast aside when they became obsolete.

But when drought conditions pushed a herd down a mountainside into Waikoloa Village in search of water about a year ago, they crossed paths with development in West Hawaii. They found themselves disrupting traffic, grazing on golf courses and keeping humans awake with their boisterous breeding.

“Even though people loved the donkeys, it was too much,” said Anika Glass of Waikoloa. “We weren’t designed to be living together.”

A major effort is now under way to capture the animals, castrate the males before the population becomes unwieldy and ship them away to new homes. The Humane Society of the United States has stepped in to foot the bill for castration and a chartered equine flight to relocate 120 of them to sanctuaries in California.

Glass created a blog, Malama Waikoloa Nightingales, that was meant to keep motorists and the donkeys safe from each other, as residents grappled with what to do. The donkeys were seen near an elementary school, tearing up back yards and getting into collisions that sometimes injured or killed the animals.

“There was a lot of concern because people were running into them,” she said. Some wanted them slaughtered and others feared they would be eradicated.

Because the donkeys made their way into the village from private property, and they weren’t considered game animals, county and state agencies were hampered from getting involved. County officials tried to repair fences in an effort to keep the donkeys from going onto roads.

“Unfortunately, because they’re not owned by anybody … it gets tricky when government goes on private property,” said Kevin Dayton, executive assistant to Hawaii County Mayor Billy Kenoi. “These are an unusual traffic hazard. The problem is, what do you do about wild animals?”

What started as about a dozen donkeys venturing into the village ended up being an estimated 400 to 600 in the Waikoloa area, said Inga Gibson, the humane society’s Hawaii state director. About 200 have been adopted to various Hawaii residents with enough space and resources to care for them. On Saturday and Sunday, a team of volunteer veterinarians castrated the males and preparing the ones bound for California, where they’ll go to the Eagle Eye Sanctuary in Sonoma and the Peaceful Valley Donkey Rescue in Tehachapi next month. The estimated cost of the castration effort and the Sept. 16 flight is $75,000, Gibson said.

Castration is a common, routine procedure for equines and more effective than constantly administering contraceptives to the female donkeys, Gibson explained: “Animals live longer, healthier lives when they’re castrated.”

Waimea veterinarian Dr. Brady Bergin said he expected about 150 donkeys to be castrated by the end of the weekend. He got involved in the donkeys’ plight when a cattle rancher called him for help.

With the donkeys roaming on his leased property, he ended up becoming a donkey rancher by default.

“It was becoming difficult for him to manage his cattle and all the donkeys,” Bergin said. “He was kind of stuck. He didn’t know what to do, but wanted to do the right thing.”

Bergin didn’t want to see the donkeys eradicated.

“We owe it to the donkeys when you look at them historically. They were beasts of burden for plantations,” he said. “Once they were no longer needed, they were thrown away.”

It’s believed the donkeys were taken to Waikoloa when development in the Kona area picked up in the 1970s, Gibson said. “The herd has just reproduced over time,” she said. The humane society undertook a similar rescue effort in the 1980s when burros in the Grand Canyon were flown to sanctuaries, she said.

The donkeys are being relocated before their population swells into the thousands, similar to a large established herd of deer on Maui. Gibson said the Waikoloa herd has been reduced by about half so far, as the effort continues to castrate the males and find the donkeys new homes.