Rare big horn sheep population threatened by single puma

Kofa bighorn ram. Credit AZFGD

August 2009. Biologists recently presented the Arizona Game and Fish Commission with compelling data indicating that recovering the critically important Kofa desert bighorn sheep herd from near record-low population levels will be challenging due to predation by a single mountain lion.

The monitoring of one radio-collared mountain lion revealed it had killed 14 bighorn sheep since February, an average of one bighorn sheep about every 10 days. At this rate, this one lion is on pace to kill an estimated 37 bighorn sheep annually. By comparison, the estimated annual yearling recruitment from the Kofa National Wildlife Refuge bighorn sheep herd is only 39 animals.

Bighorn lamb killed
Additionally, biologists reported last week that the same radio-collared lion has made a 15th kill. The animal killed was a bighorn lamb within the Kofa Predation Management Area near the Little Horn Mountains.

"The rate at which this lion is preying on bighorn sheep is of grave concern," said Game and Fish Yuma Regional Supervisor Pat Barber.

Eleven of the bighorn sheep killed were within the department's Kofa Mountains Complex Predation Management Area. This management area includes all of the Kofa National Wildlife Refuge (NWR) and three key areas that extend slightly beyond the refuge to encompass contiguous mountain ranges not captured by the Refuge boundaries. These areas contain habitats used by Kofa NWR bighorn sheep population.

Although managers are working to address several issues that might limit sheep recovery, such as water availability, disease and human disturbance, predation at this level remains a significant concern.

Past surveys indicate that, historically, mountain lions were virtually non-existent or only transient guests around the Kofa region. However, in recent years, a number of lions have become residents on and around the Kofa NWR and are having a significant impact on the bighorn sheep population.

3-5 mountain lions present
Furthermore, officials estimate there are three to five other mountain lions in the Kofa Mountains Complex Predation Management Area. Conservative modelling of four mountain lions (three males and one female) suggests predation could exceed the annual bighorn sheep recruitment by more than 150 percent.

"Once a localized wildlife population has zero recruitment or less, meaning it's not replacing lost animals from standard mortalities, it's just a matter of time before that population is extirpated." said Game and Fish Wildlife Specialist John Hervert.

Arizona mountain lions
The mountain lion population in Arizona is neither threatened, endangered, or at risk, and they are the most broadly distributed large mammal species in North America.

The concern over declining bighorn sheep populations is not unique to Arizona. There are a number of distinct bighorn sheep populations that have required federal listing through the Endangered Species Act, in part or exclusively due to mountain lion depredation, including the Peninsular, Sierra Nevada and the San Gabriel Mountain bighorn sheep populations. Recovery efforts for those populations will cost millions of dollars.
For history on the struggling Kofa bighorn sheep population, visit www.azgfd.gov/kofa