Relative Abundance and Anthropogenic Disturbance Effects on the Burrowing Owl (Athene cunicularia) in Grasslands of the Southern Chihuahuan Desert, Mexico

Grassland ecosystems are among the most threatened habitats in North America, and their degradation has contributed to widespread population declines of grassland-dependent birds. The Burrowing Owl (Athene cunicularia) is a grassland specialist whose populations have shown sustained declines at a continental scale; however, quantitative data on relative abundance remain limited in northern Mexico. We estimated a relative abundance index for the Burrowing Owl in the grasslands of the southern Chihuahuan Desert, Mexico, using vehicle-based line transects expressed as the number of individuals per linear kilometer (ind/km). Additionally, we evaluated the relationship between human disturbance and owl records using a standardized Human Disturbance Index (HDI) based on field indicators of grazing pressure and solid waste. A total of 18 transects (1 km each) yielded 83 detections, with a mean relative abundance of 4.61 ± 5.93 standard deviation (SD) ind/km. A Generalized Linear Model with a Negative Binomial distribution revealed a significant negative effect of the HDI on owl abundance (β = −1.27, z = −3.81, p = 0.0001; incidence rate ratio (IRR) = 0.28, 95% confidence interval (CI): 0.14–0.51). Our results provide a baseline abundance estimate for the Burrowing Owl in the southern Chihuahuan Desert and highlight the importance of habitat disturbance metrics to assess population status in fragmented and human-impacted grassland landscapes.