Death Valley’s invasive donkeys have become cat food

On an early June morning in Death Valley National Park, a wild donkey brought her foal to one of the springs scattered across the desert. Two pairs of eyes watched as the foal picked its way through the undergrowth. One set belonged to a mountain lion, the other to a wildlife camera.

Footage of the subsequent kill was published in the Journal of Animal Ecology last month, in a study that provided direct evidence that mountain lions hunted donkeys in the western deserts of North America. The attacks don’t just result in donkey waste and stuffed cougars, researchers argue: They suggest that native carnivores are an important control over non-native prey. The study also raises questions about how harmful donkeys are in the wild desert landscapes where they are found, despite federal wildlife agencies’ goal of eliminating them entirely.

Donkeys are originally from North Africa but were introduced to the United States by the mining industry in the late 19th century. Federal authorities were not pleased to see the hardy herbivores making their home in Death Valley. In the 1930s, wildlife managers began culling donkeys, arguing that herds of donkeys were trampling vegetation, silting up springs and driving away native wildlife such as bighorn sheep. But the donkeys stayed, and decades later an estimated 4,000 live in Death Valley, despite National Park Service goals to bring the population to zero.

Erick Lundgren, a biologist at Aarhus University in Denmark, was interested in the impact of donkeys on desert wetlands. First, he focused on the donkeys’ habit of digging wells – sometimes as deep as five feet – to reach water from beneath dry stream beds. These wells have often been cited as evidence of ecological damage, said Dr. Lundgren. But he and his colleagues found in a 2021 study that donkey wells served as nurseries and havens for native plants and animals.

He also found that donkeys that congregate near campsites in Death Valley could cause harm.

“They’re pretty much turning these wetlands into a maze of trails and trampled ground,” said Dr. Lundgren. While some plant species do benefit from this type of grazing, he added, the donkeys destroy other types of vegetation that attract birds and store carbon.

dr However, Lundgren found that in more remote, spring-fed groves, donkeys tended not to linger and their effects on vegetation were much less drastic. In many places, the researchers found mountain lion caches — the hidden carcasses hidden behind boulders or thickets to deter theft from scavengers and other cats. Many of Death Valley’s caches contained donkey remains, suggesting that donkeys served an important ecological function in parts of the park: cat food.

dr Lundgren and his colleagues surveyed 13 different wetlands using camera traps. Eight of the sites, often the more mountainous sites, showed the remains of donkey kills. In such locations, donkeys appeared to be the predators’ main prey, making up 24 of the 29 hidden carcasses.

These spots had half as much trampled ground and almost twice as much canopy compared to the springs around campgrounds, where fewer lions roamed.

“Our study shows that donkeys can bare wetlands, but only when there are no mountain lions,” said Dr. Lundgren. “This is the case in the most visible springs in Death Valley, which arise in campsites where mountain lions are afraid to go,” said Dr. Lundgren. He said the places where wild donkeys do the most damage are “places that are artificially safe because of people.”

In other words, the predators served as a control for the donkeys, said Dr. Lundgren, and mitigated their impact on sensitive sites into something ecologically beneficial—digging well and opening up spring-fed thickets.

The Federal Agency for Wildlife disagreed with the researchers’ conclusion.

“Puma predators are insufficient to control feral donkey populations in the park, which reproduce at a rate of about 20 percent each year, and do not contribute significantly to the management goal of zero non-native donkeys in the park,” said Abigail Wines, enlisted Management Assistant at the National Park Service.

dr Lundgren replied that the donkey birth rate quoted by Ms Wines was based on estimates dating back decades. In Death Valley, he said, concrete figures on donkey populations are hard to come by. He also pointed to research that suggests mountain lions are potentially important predators for wild horses and donkeys. A 1999 study found that mountain lions helped control a feral horse population in Nevada, while a 2021 study found that some cats in the same region depended solely on feral horses for prey. That could mean mountain lions that prey on non-native donkeys in Death Valley may not hunt as many endangered species there as bighorn sheep, said Dr. Lundgren.

Park staff declined to answer questions about the achievability of having no donkeys in Death Valley, but in the past they have acknowledged that eliminating donkeys there entirely is, at best, a desirable goal. “We’ll always have donkeys,” Alison Ainsworth, then a biologist at Death Valley National Park, told Undark Magazine in 2019, noting that herds continue to roam the surrounding state.

If the donkeys are now an integral part of the landscape, argues Dr. Lundgren, it pays to see them as potential parts of a working ecosystem, not alien.

“A lot of the population numbers you hear, and these stories about how terribly invasive these animals are, ignore the fact that predators can hunt them, especially if we leave those predators alone,” he said.

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