Making a killing to save Arizona's desert bighorn sheep
A mountain lion paid the ultimate price for his gluttony after helping himself to too many servings of lamb and venison near southwestern Arizona’s Kofa National Wildlife Refuge. Earlier this month wildlife officials killed the lion as it guarded the fresh carcasses of two desert bighorn sheep and a mule deer. The lion threatened recovery of a faltering sheep species in the refuge. But even as the Arizona Game and Fish Department dispatched wildlife officers to destroy the offending puma, the department offered hunters 12 licenses to kill desert bighorn sheep in the protected wildlife area. Although predation threatens the vulnerable sheep herd, paradoxically, targeted hunting of rams may actually help save the desert bighorn sheep from extinction.
“This is not about hunting lions,” or sheep, says Gary Hovatter, an information and education program manager for the Arizona Game and Fish Department. “It’s about restoring bighorn sheep herds.”
Established in 1939, the Kofa National Wildlife Refuge encompasses more than 600,000 acres and serves as one of the few remaining habitats for desert bighorn sheep. The rugged Kofa and Castle Dome Mountains rise steeply from the scrublands that epitomize this desert habitat. In the refuge, desert bighorn sheep share their home with desert tortoise, desert kit fox and now desert mountain lions.
Bighorn sheep numbers in Kofa have dropped in the past few years from more than 800 individuals in 2000 to around 390 by last year. Ecologists attribute sheep declines primarily to cycles of drought, with sheep recovering during years with greater rainfall. But recently, the number of sheep has dropped in spite of more rain, and biologists blame mountain lions.
At least five mountain lions now live in the refuge, according to recent surveys, including one lion with cubs. “The single biggest change in the Kofa was the establishment of a resident lion population,” says Hovatter. “For almost a hundred years, there’s been no history of a mountain lion population here.”
Mountain lions kill one large game animal a week on average, and with at least five lions residing in Kofa, wildlife managers worry that the cats could over-hunt vulnerable game populations like the desert bighorn sheep.
The young male lion killed last week was an overzealous hunter, says Bob Henry, a biologist with the Arizona Game and Fish Department. “We had five documented kills in three months, period,” he says, referring to the three animals the lion hoarded and two others from another kill site.
In the most recent attacks, Hovatter thinks the lion was staking out a watering hole in the refuge, “killing every big game animal that came to the water.”
And game and fish officials worry about the potential for more losses. Four of the five animals killed by the lion were bighorn, including three ewes, a significant loss, especially when considered in a larger context: Since bighorn populations increase at the annual rate of 17 yearlings per 100 ewes, Hovatter says, "this lion's kills accounted for the annual recruitment we would expect to get from 25 ewes."
Now biologists plan to backtrack the puma’s whereabouts using previously recorded satellite data, so they can search for other animals killed by the lion.
While some decry killing mountain lions in a wildlife refuge, game and fish officials explain that destroying the animal is a better choice than relocating it. Capturing and moving lions stress them, and once placed in a new habitat they fight with, and are often killed by, other lions. Sometimes they starve to death.
Paul Krausman, a professor of wildlife conservation and management at the University of Arizona in Tucson, calls the behavior of this cougar atypical. “I’ve never seen a situation where you have three big fresh kills at once, especially with a young male lion,” says Krausman. “But,” he concedes, “it is possible.”
Even so, Krausman continues, “I don’t think those five lions would devastate the sheep population. If they do, then there’s something else wrong with [the sheep].”
In fact, the struggling herd contends with other challenges made worse by a cougar killing ewes. The herd currently has an imbalance of rams to ewes, creating a situation similar to a small town where men outnumber women. When a bunch of men hound the one woman in the bar, tensions may erupt in an all out brawl, leaving everyone exhausted. In Kofa, a few dominant rams guard as many ewes as they can; the remaining rams roam the edges of those groups, hoping to gain access to the females. So hunting rams can actually relieve some of the stress on the bighorn sheep ewes.
Hunting has other benefits for conservation, says Hovatter. Money from licenses funds conservation projects, protecting habitat for many species. And hunting groups sometimes volunteer time to assist ecologists with fieldwork.
Wildlife managers hope their seemingly paradoxical strategy will boost sheep numbers high enough in Kofa that they can then reintroduce them in other areas.
“The Kofa is some of the most rugged country in the United States,” says Krausman, “It’s amazing to go out there and see bighorn sheep surviving.”