Three more bighorn sheep die in Catalina Mountains

Three more bighorn sheep have died in the Catalina Mountains north of Tucson this month — two of them falling prey to mountain lions and the other dying of an undetermined cause.

Meanwhile, all but two of the GPS tracking collars on surviving bighorns brought to the Catalinas in 2013 have dropped off, decreasing the number of collared sheep in the range by nine. The collars are designed to fall off automatically when their power source runs out after approximately two years.

Following the recent deaths, 45 collared bighorns are known to be alive, including animals brought to the Catalinas in 2013, 2014 and 2015. But the total number of surviving sheep could be as high as 54 if all nine sheep that lost their collars are still living.

“Plus, there is at least one new lamb on the mountain,” observed on Jan. 10, said Mark Hart, spokesman for the Arizona Game and Fish Department. The agency is overseeing an effort to rebuild a bighorn herd that disappeared from the Catalinas in the 1990s.

It’s possible that four or five more lambs have been born recently as well, Hart said, noting that lambs born on the mountain aren’t equipped with GPS collars.

RECENT BIGHORN DEATHS

A Game and Fish Department report provided details on the sheep deaths this month.

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• One ewe died on Jan. 5 northeast of Biosphere 2 as a result of mountain lion predation. “This predation event occurred outside of the project’s designated area for administrative mountain lion removals, so no attempt was made to locate the lion responsible for the kill,” the report said.
• A second ewe died on Jan. 7. Predation was ruled out, but the cause of death wasn’t determined.
• Another ewe died on Jan. 8 as a result of mountain lion predation, possibly involving two or three lions. Pursuit of the lions was unsuccessful.

FALLING PREY

The occurrence of bighorns falling prey to mountain lions had declined since the early months of the reintroduction effort in 2013 and 2014 — until now. The reasons for the uptick in predation aren’t certain, but Hart suggested one possibility.

He noted that the recent predation victims were bighorns that were brought to the Catalinas in November 2015 and had little time to adapt to terrain in the range.

“Sometimes we see sheep that are new to the mountain exploring new territory outside of the preferred habitat” where other bighorns are thriving, Hart said. “It’s unfamiliar terrain. The sheep were unfamiliar with the mountain, and that could make them more vulnerable” to predation.

“To the extent it contributed to their cause of death, we can’t be sure,” Hart said. “But it’s worth noting that they were new to the mountain and learning the territory.”