Lions and helicopters
California Department of Fish and Wildlife documented last winter that a significant portion of our Sierra vighorns remained at higher elevations for the winter, despite record snowfall conditions. Many of these bighorns succumbed to starvation, avalanches, or other risks associated with extreme snow depths. The inference for this behavior was to avoid lion predation. I agree with this assumption as a natural behavior of a species that lions have preyed upon since day one.
I feel strongly there is another factor that contributed to this behavior. Some herds (i.e. Wheeler Ridge, Sawmill) have been subjected to regular, if not annual, helicopter operations where they are chased, net gunned, collared, tagged, blood sampled, pregnancy tested ... by CDFW. Although well intended, these operations are a terrifying experience for the sheep. It is my opinion, shared by many, that lower elevation avoidance in these cases is a learned behavior response due to regular harassment by helicopters; in addition to avoiding lions and other predators. The sheep have learned that every time they come down for spring green up, there is a good chance a helicopter will show up.
To compound the issue, these operations are conducted at a critical time (usually March) whereby bighorn have persisted through a tough winter and are looking for spring forage to start building fat reserves. The females (ewes) are also in late pregnancy stages. Unfortunately, these operations have as incidental results mortality, broken bones, and even lambs being aborted. A small percentage and risks but this happens more regularly than CDFW would like you to know.
I would highly recommend that if a herd is subjected to helicopter operations, there is a lag of several years before this occurs again. I recognize that these operations are sometimes essential to recovering the species and you have to weigh the pluses and minuses. But hopefully as we move forward lessons have been learned. We’ll never know for sure whether sheep are avoiding lions, helicopters, or both. I say error on the caution side.
Brian Tillemans Bishop