Validation of the use of unmanned aerial vehicles for population assessment of the bighorn sheep (Ovis canadensis mexicana Shaw) in the Sonoran Desert

Resumen

Objective: To evaluate the use of drones for population monitoring of the desert bighorn sheep in two Wildlife Management Units (WMUs) of the Sonoran Desert.

Design/methodology/approach: Fieldwork was conducted at El Tonuco and Chaparral Ranches, Sonora, during the summer seasons of 2020 and 2021. Direct observations of bighorn sheep were initially carried out, followed by the use of drones to record individual animals. Relative abundance was estimated according to sex and age class. To assess the effectiveness of drone usage, results were compared to those obtained through direct monitoring using the non-parametric Mann–Whitney U test, correction factor, and detectability percentage.

Results: Drone monitoring recorded 118 and 96 bighorn sheep in El Tonuco and Chaparral Ranches, respectively, representing 2.26 and 1.31 times more individuals than those detected through direct observations. Females constituted the most frequently recorded group. No significant differences were found in bighorn sheep abundance between the two monitoring techniques. At El Tonuco Ranch, the correction factor for population estimates based on direct observations, in comparison to drone data, was 62%, while at El Chaparral Ranch it was 24%. This factor varied significantly according to sex and age class (P ≤ 0.05).

Study limitations/implications: It is recommended to complement the findings with geospatial analyses and to replicate this methodology in other key sites for the conservation of desert bighorn sheep.

Findings/conclusions: The use of drones proved to be a more efficient tool than direct transect observations for detecting bighorn sheep.