TUCSON, Ariz. (AP) — An estimated 85 bighorn sheep were living in the Santa Catalina Mountains near Tucson this spring after a reintroduction effort that began four years ago, according to Arizona Game and Fish Department officials.

Game and Fish spokesman Mark Hart said a March survey revealed the extent of the bighorn population. Another count was performed recently and a second one that could happen next month should provide a more thorough accounting of how many bighorn are in the mountains.

The Arizona Daily Star reports the sheep appear to be thriving after the rare species was brought back to the mountains northeast of Tucson starting in 2013.

Thirty bighorns were released in the mountains that year and more were brought in each of the next three years. The sheep struggled at first, with mountain lions and disease leading to a number of deaths. The population stabilized when sheep congregated in steep, rocky habitat in the Pusch Ridge area of the Catalinas.

Desert bighorns disappeared from the range in the late 1990s, but the webpage of the Catalina Bighorn Restoration Committee says they are not a threatened species and that more than 5,500 live in Arizona.

Hart said it is difficult to count the bighorn because tracking collars on only 32 of the released sheep still operate.

The actual number is likely more than double that number, Hart said.

Wildlife officers reported that 19 lambs were born this year and their survival rate was an unusually high rate of 50 percent, Hart said. Two bighorns were killed by cougars over the last year.

"We would characterize the bighorn population as stable, with the size of it as of yet undetermined," he said. "There is no evidence of disease or that there have been a lot of kills by mountain lions."

Game and Fish has stopped pursuing lions that attack bighorns a year ago.

An advisory committee recommended in 2013 that the department reintroduce bighorns to the mountain range.

An aerial survey of the herd's habitat was conducted Sept. 30, but Hart said a reliable population estimate won't be available until wildlife officers analyze photos from the survey.

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Information from: Arizona Daily Star, http://www.tucson.com