The California Department of Fish and Wildlife says a survey earlier this month counted 60 bighorns in the Mount San Gorgonio region east of Los Angeles. That's down two-thirds from a survey conducted in 2016.
Biologist Jeff Villepique says in the past, such die-offs have been triggered by an outbreak of a respiratory disease spread by contact with domestic sheep or goats.
The disease killed at least 21 bighorns whose carcasses were found in the area in December.
Southern California has about 4,800 desert bighorn sheep in 64 herds. Authorities say so far, sheep in nearby herds haven't been affected.
Copyright 2019 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.