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

Abstract

Objective: Evaluation of drone use for population monitoring of desert bighorn sheep in two ranches of the Sonoran Desert.

Design/methodology/approach: At Rancho El Tonuco and Chaparral, Sonora, during the summer season 2020 and 2021, direct observations of bighorn sheep were conducted. Subsequently, a drone was used to record the individuals. Relative abundance was estimated based on sex and age. To evaluate the effectiveness of using drones, the results were compared with those obtained through direct monitoring, using the non-parametric Mann–Whitney U test, the correction factor, and the detectability percentage.

Results: Using drones, 118 and 96 bighorn sheep were recorded in the El Tonuco and Chaparral ranches, respectively, which is 2.26 and 1.31 times more than direct observations. Females were the most frequently recorded group. Significant differences (P≤0.05) were found in sheep abundance depending on the monitoring technique used. In El Tonuco Ranch, the correction factor for population estimation based on direct observations, compared to drone use, was 62%, while in El Chaparral Ranch, it was 24%. This factor varied according to sex and age class (P≤0.05).

Limitations on study/implications: It is recommended to complement the study results with geospatial analysis and replicate this methodology in other key sites for the conservation of bighorn sheep.

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