Desert Bighorns Decline
November 04, 2010
Mountain lions take a toll on sheep on the Kofa National Wildlife Refuge in Arizona.
For several years, desert bighorn sheep on the Kofa National Wildlife Refuge in Arizona have been a source of controversy. This refuge was established in 1939 to help in the recovery of desert bighorn sheep, and the program worked as 800-1,000 bighorns occupied the area for many years. In fact, over the years, because sheep numbers remained high, the Kofa served as a source of sheep for transplanting, and sheep captured on the refuge are now thriving in several other locations in Arizona. Today, at least four other areas in Arizona could support bighorns if the Kofa sheep numbers were high enough to allow for more capture and relocations. Unfortunately, that is not likely to happen for a while.
Controversy first started in 2007 when several animal-rightists (sometimes referred to as environmental groups, although that is a stretch in most instances) entered legal arguments to prevent construction of water sources for wildlife (including bighorns) because they felt such work violated the Wilderness Act. In 2008, a judge ruled to allow the construction, and the customary appeal was denied in 2009.
During that same time period, an even bigger problem was unfolding: Mountain lions began taking a heavy toll on the sheep. Prior to 2003 (in 1944), only one lion had ever been seen on the refuge, but as bighorn numbers grew, the lions came. In fact, a DNA study showed 11 lions there from 2007-2009. Apparently lions have had an impact on sheep numbers. In 2000, there were 812 bighorns on the refuge, 436 in 2008, and 410 in 2009. Because the desert bighorn population on the Kofa is so important for translocations, the U.S. Fish and Wildlife Service and the Arizona Game and Fish Department are conducting ongoing research and surveys. They suspect that a number of factors including drought, disease, water, and predation could be depleting sheep numbers.
In recent years, biologists have examined 100 sheep kills and found that lions have killed most of those sheep. One lion collared in February 2009 killed 14 sheep in the six months after it was collared. Annual yearling sheep recruitment on the Kofa is 39 lambs per 100 ewes, so this one lion was seriously depressing reproductive success. If the reproduction rate is not high enough to replace lost animals, then the population will eventually plummet. Some people believe that without proper management, mountain lions could totally eliminate bighorns from the Kofa.
The Arizona Game and Fish Department's Predator Management Plan for the Kofa allows for the removal of lions that are particularly harmful to bighorn sheep. Under this plan, a problem lion was lethally removed in September 2009. In late May 2010, the Fish and Wildlife Service announced the implementation of its predator control program on the Kofa under which a lion may be lethally removed or translocated if it kills two sheep in a six-month period. This removal can take place when the bighorn population falls below 600. When sheep numbers grow to 800 or higher, no lions will be removed. Although some people oppose any lion management whatsoever, this is an excellent management plan that allows bighorns and mountain lions to coexist and benefits all visitors to the Kofa National Wildlife Refuge.
Fallow Deer Sing Bass
On a lighter note, much evidence indicates that buck deer, bull elk, and other big game males become more dominant as they get older (at least to a point). More-dominant males also do most of the breeding. Okay, I admit it isn't quite that cut and dried, but in general, it's true.
Recent research adds one other component to this phenomenon. In Ireland, over consecutive years researchers recorded the breeding season "groans" of individual male fallow deer, and they found that the "acoustic quality" of stag calls changed with age.
Apparently, changing body conditions in aging males affects their calls.
The researchers go on to suggest that other stags recognize this change and use this to reduce fighting because, based on the sounds of their calls, they recognize the dominant stags. In addition, the researchers believe that the variations in calls allow females to recognize more-dominant stags from previous years' interactions. When I was in college, I lowered my voice to sound more impressive, and it did nothing for me. I still didn't get dates for the big dance. But apparently fallow deer have perfected the technique.