Silver Bell Bighorn Herd in Trouble

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The fate of the desert bighorn sheep population in the Silver Bell Mountains 30 miles east of Tucson is still in doubt following an outbreak of pink eye in December, which has resulted in 30 bighorns going blind and 12 of those animals dying.

Arizona Game and Fish Department biologists have been routinely flying the area to capture and treat bighorns for keratoconjunctivitus—commonly known as pink eye. DNA testing shows that the bighorns caught the disease from domestic goats that escaped from an adjacent grazing lease near the Ironwood National Forest.

Gerry Perry, the Tucson regional supervisor for the Game and Fish Department, says the Silver Bell Sheep population is historically and biologically significant. “This bighorn population has been there since the Pleistocene era. In fact, it is the only remaining indigenous population of bighorns in southern Arizona. Therefore, it represents an irreplaceable source of genetic variation for desert bighorns.”

Here is the current status of the 30 bighorns documented as being blind:

- 12 bighorns have died—five from malnutrition or starvation, five from mountain lion predation, and two are awaiting necropsy to determine cause of death.

- 10 have recovered their sight and are doing well.

- The status is unknown for the others.

Blindness is not the only medical problem facing the Silver Bell sheep population. The bighorns are also suffering from another disease called contagious ecthyma, which is also known as sore mouth. It is an acute infectious viral disease of sheep and goats that causes skin lesions. Such lesions can cause a mother to refuse to nurse her baby. This is the lambing season for bighorns.

Biologists have documented 16 bighorns with sore mouth. Here is their current status:

- Five still have clinical signs of the disease (one is a lamb that is apparently still nursing).

- Six have recovered.

- The status of three animals is unknown.

- Two bighorns have died: the deaths were related to the fact that they were blind, rather than from sore mouth.

The outlook is not good. “We are concerned because we could lose a large portion of the bighorn sheep lamb crop this year in the Silver Bells, which further compounds the losses due to disease. I don’t like to sound pessimistic, but this could become a dire situation for this bighorn population,” Perry says.