Mountain sheep Ovis canadensis and helicopter surveys: Ramifications for the conservation of large mammals

Mountain sheep did not habituate or become sensitized to repeated helicopter overflights, and the negative influence of the helicopter was extreme and may override variables that might otherwise be correlated with movement patterns of mountain sheep.

Abstract

Mountain sheep Ovis canadensis respond dramatically to helicopter disturbance. Significantly more animals abandoned sampling blocks and moved farther during helicopter surveys than on nonsurvey days throughout the year. Likewise, mountain sheep changed the vegetation type they occurred in more often after than before helicopter surveys; however, this difference was only significant during spring. Mountain sheep did not habituate or become sensitized to repeated helicopter overflights: time since capture was not related to their movements. The negative influence of the helicopter was extreme and may override variables that might otherwise be correlated with movement patterns of mountain sheep: this outcome also may hold for other ungulates. Further, sampling with helicopters may result in the violation of fundamental assumptions of population estimators routinely employed in conservation efforts for large mammals. The consequences of disturbing mountain sheep, such as altering use of habitat, increasing susceptibility to predation, or increasing nutritional stress, need additional study. These factors all have ramifications for the conservation of mountain sheep and other large mammals disturbed by helicopter sampling.