Wild donkeys roam unchecked in the Mojave and Sonoran deserts, which cover a good chunk of Southern California and Northern Mexico, as well as Death Valley National Park in California. They travel in large herds, trampling the wetlands in search of water sources. The wetlands provide life-giving water and habitats for many native species in the dry desert areas.
These wandering burros are considered invasive by the National Park Service. They have no natural predators that can keep their population under control. Until now.
A recent ecological study published in the Journal of Animal Ecology has found that mountain lions have been killing feral donkeys in the desert. “We have imagery of a donkey group going by and then a cougar right behind them, like literally walking in their footsteps,” said lead author on the study and ecologist at Aarhus University Erick Lundgren.
Lundgren and his scientists studied donkeys and mountain lions specifically in Death Valley. They realized that the donkey herds avoided wetland areas where other donkeys had been previously attacked by cougars. Wetland areas where donkeys were preyed on were also less trampled than before, as the donkeys steered clear of those areas after attacks. The findings highlighted how important predators are for maintaining invasive and out-of-control populations, according to Smithsonian Magazine.
Researchers monitored 14 different wetland areas, using cameras to watch the donkey-mountain lion interactions. They confirmed cougars killing donkeys at 8 different locations. The researchers also visited these locations in person to search for carcasses, which mountain lions will often leave behind and come back to later. Lundgren said, “Some of these cache sites were used over and over again, so that every time we went, there would be three or four fresh kills.”
Ecologists Study Invasive Donkeys Versus Mountain Lions, Highlight Importance of Apex Predators
Additionally, donkeys in cougar-prone areas would only venture out during the day. In areas where cougars had not attacked, the donkeys were seen day and night. These were areas where the researchers found more trampled vegetation in the wetlands.
“These sites where they’re there all day, they’re trampling and eating the vegetation,” explained Lundgren. “It really strongly leads to a lot of bare open ground, a lot of dung, and then a really strong reduction in plant cover.”
In areas where cougars were actively seen killing donkeys, researchers reported more canopy cover. There was also less bare ground, and more vegetation around water sources. This influences species further down the food chain. This phenomenon is called trophic cascade. Those at the top of the food chain indirectly influence those at the bottom. So, wild feral donkeys: not so good for the environment. Mountain lions? The unexpected conservationists protecting the wetlands.
This study hopes to help bring the mountain lion into a more positive light. But Lundgren also hopes that we don’t start viewing the donkey as an inherently negative species. He warns that killing or removing the feral donkeys could lead to the mountain lions moving on to other prey. Mathias Pires, ecologist at the University of Campinas, agrees with that sentiment.
“Unless we have very good information on how things are connected to each other and affect each other,” he said, “we might make bad decisions.”