Integrating Callback and Acoustic Surveys to Determine Drivers of Canyon Occupancy by Mexican Spotted Owls at Grand Canyon National Park

Abstract

Mexican Spotted Owls (Strix occidentalis lucida) are a federally threatened subspecies of Spotted Owl that occupy forests and canyons across the Desert Southwest of the USA. While Mexican Spotted Owls in forest habitat are well studied, those occupying canyon habitats are underrepresented in the literature. We used data from callback surveys from 2001–2021 and autonomous recording units (ARUs) from 2019–2021 in a multi-method, multi-season occupancy model to assess long-term occupancy of 33 management units (called protected activity centers [PACs]) in Grand Canyon National Park. We assessed survey effort and determined how vegetation diversity, side-canyon topographic complexity, and shrub cover influenced occupancy. Results derived from our model suggested that populations of Mexican Spotted Owls in the Grand Canyon remained stable over the last two decades. Owls preferentially occupied PACs with higher diversity of vegetation types during the breeding season, whereas canyon complexity and shrub cover did not have a strong effect on occupancy. Callback surveys were more effective than ARUs at detecting owls on a single night (mean probability of detection = 0.74 and 0.38, respectively). However, ARUs expanded the survey season into February and allowed more PACs to be sampled over multiple nights with less field effort. Conducting surveys early in the breeding season improved detection probability regardless of method. Overall, our study highlighted PACs that have been under surveyed across the study period, identified habitat features that are consistent with long-term PAC occupancy, and demonstrated the potential to combine traditional callback survey data with ARU data to more effectively monitor Mexican Spotted Owls.

Citation

Fuller, Kirsten; Jones, Gavin; Terwilliger, Miranda; Reid, Dana S.; Cruz, Jennyffer. 2026. Integrating Callback and Acoustic Surveys to Determine Drivers of Canyon Occupancy by Mexican Spotted Owls at Grand Canyon National Park. Journal of Raptor Research. 60(4): 1-19. https://doi.org/10.3356/jrr26006.