Wild Horse Woes: High Numbers Continue to Be Problematic

Years ago, while sitting in a ground blind at a water hole in a remote area of the Red Desert in Wyoming, I had wild horses come to drink. It was a magnificent sight that is permanently etched in my brain. I’d subsequently enjoy other sightings of wild horses while antelope hunting in Wyoming. I must admit those experiences biased my thoughts on whether wild horses belong in the wild, even though they are not a native species to our country, having been brought here centuries ago by explorers and settlers.

Of course, ring-necked pheasants aren’t native to the Dakotas or other western states, but no one questions whether they belong. Pheasant hunters sure love them, and the states with them like the money they bring to their economies.

The Dilemma

However, the wild horse situation is far different than that of pheasants. The U.S. Bureau of Land Management (BLM) and the USDA Forest Service are responsible for managing wild horses and burros on public lands. There are 179 Herd Management Areas located across 32 million acres of public lands in the western United States. Surveys of most of those herds are conducted every four years from aircraft. Then a carrying capacity is determined for the number of horses and burros they want on those herd management areas. The horses compete for food with mule deer, antelope and bighorn sheep, species native to many of those same lands. Normally, native species have priority over a non-native species. However, many citizens like seeing wild horses on the landscape and have even gotten federal legislation passed to protect the horses. The Wild Free-Roaming Horses and Burros Act of 1971 mandates that BLM follows a horse and burro management plan leading to an ecological balance where the horses and burros are an integral part of the natural system of public lands. Easier said than done.

Wild horses are in the news every year when BLM rounds up horses to bring numbers down closer to the carrying capacity. They then capture them and place them in pens. From there, attempts are made to sell them to anyone who wants a wild horse. There are never enough buyers for the horses captured, so holding them gets to be a bigger government expense every year. One major effort at solving this problem is sterilization to control breeding of the horses. Chemosterilant research has been done on female horses, and it works to a degree. However, it doesn’t prevent pregnancy for many years, and the chemosterilant must be readministered. That can be done by recapturing the same female horse and administering it, or by using a capture gun in the wild. Either way, it is expensive and difficult. What is needed is a chemosterilant that lasts a lifetime. Progress in using chemosterilants on wild horses is slow, but it continues. The truth is, it may never solve the wild horse problem. Shooting excess horses is not possible under federal law.

With horse numbers being a problem, any study that shows that something is eliminating some horses will draw attention. Thus, the study I’ll describe has some importance in the discussion of wild horses on the landscape.

What About Predators?

First, let me clarify where researchers did a study that showed that mountain lion kill wild horses. They studied what mountain lions were eating in the Sierra Nevada mountain range and the Great Basin. Both are extremely dry areas. The Sierra Nevadas are 400 miles long and 80 miles wide, stretching from northern California south. The range is in California and butts up against the border of Nevada on the east side and the valley of central California on the west side.

The Great Basin is literally all of Nevada, most of Utah, and some of Idaho, Oregon and Wyoming. The Great Basin is more open terrain and has wild horses along with other prominent prey species for mountain lions. These include mule deer, antelope and bighorn sheep. Cougars eat all these species, but in the Great Basin they kill lots of horses. They don’t kill enough to solve the wild horse problem, but they kill more than we ever knew about. We assumed the body size of the horses and habitat characteristics prevented much horse predation by the cats. That’s apparently not true. Researchers found few wild horses living in the Sierra Nevada Mountains, but lots of mule deer. However, there have been some reports of wild horses there being killed by cougars.

Researchers put GPS tracking collars on 21 mountain lions in the western Great Basin (5 males, 8 females) and the eastern Sierra Nevada Mountains (2 males, 6 females). By monitoring the cats’ locations with the GPS collars, they could tell when cats spent time in one area, and/or continued to return to that area, meaning there was probably a kill there. With this approach, they were able to investigate 1,310 potential kill sites and locate prey remains of 820 predation events. Mule deer made up 91 percent of the prey items found on the Sierra Nevada Mountain range side of the study area, but only 29 percent of the prey items on the Great Basin side of the study area.

Free-roaming horses dominated the diet for 13 cougars living in the Great Basin study area. Wild horses made up 60 percent of the prey items found in the Great Basin and were regularly killed by 10 cougars (of the 13 they had collars on). Wild horses were the primary diet item for eight of the collared cougars. In the Great Basin, cougars killed 0.38 horses a week, on average. Here is another interesting fact: Great Basin female cats killed and ate all age groups of horses, but males tended to eat young horses in the spring and summer and switched to mule deer in the winter.

As mentioned above, cougar predation probably won’t limit the growth of horse populations, but they are an effective predator of horses of all ages. The conclusion is relatively simple. If horses and mountain lions occur in the same area, lions will kill horses. This study adds information on wild horses as prey that wasn’t known before. Predator-prey systems are complex, and now we have one additional piece to the puzzle. Based on this research, cougars are not the solution to the wild horse problem.

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