Mammals of Rancho El Aribabi in the Sky Island Region of Sonora, Mexico.

From 2006 to 2018, we inventoried and studied the ecology of mammals at Rancho El Aribabi, a conservation ranch located in the sky island region of northeastern Sonora about 60 km SSE of Nogales, Sonora/Arizona. The results are based on 4.5 years of camera trapping (2014–2018), small mammal live trapping, mist-netting for bats, a review of previous work in the region, and our visual observations. We documented 36 species of mammals in 20 families. A species accumulation curve suggests that we documented most, or all, of the medium to large wild mammals (20 species) after 2.5 years of camera trapping. One species, the jaguar (Panthera onca), was found by others during 2010–2011, but not by us. The North American porcupine (Erethizon dorsatum) has not been observed on the ranch for 20–30 years. Our limited surveys of small mammals and bats documented six species of small, terrestrial mammals and eight species of bats. Many other species of small mammals and bats are expected at the ranch based on previous work in the region and we plan to conduct future assessments for their presence. Camera trap images allowed us to study the ecological aspects of medium to large mammals, including among others, breeding chronology, litter size, group size, 24-hour activity patterns, monthly activity patterns, predation and other behaviors, naïve occupancy, and relative abundance. To examine associations of several species with various habitat features and human disturbance, we conducted binary logistic regression modeling for nine taxa: desert cottontail (Sylvilagus audubonii), rock squirrel (Otospermophilus variegatus), bobcat (Lynx rufus), puma (Puma concolor), hog-nosed skunk (Conepatus leuconotus), hooded skunk (Mephitis macroura), ringtail (Bassariscus astutus), white-nosed coati (Nasua narica), and common raccoon (Procyon lotor). At Arroyo Las Palomas in the Sierra Azul, we compared relative abundance of 11 medium to large mammals during periods without cattle versus often heavy cattle use to discern effects of livestock grazing on those species. Livestock had a negative effect on six of those 11 species. We also assessed the potential for competition between hog-nosed and hooded skunks, and bobcats and ocelots (Leopardus pardalis). Potential effects of puma on coyote (Canis latrans) populations were also examined. The mammalian fauna of Rancho El Aribabi is similar to that found in other sky islands of northeastern Sonora and southeastern Arizona. In addition, it supports the northern-most known breeding population of ocelots, and relative abundance of other neotropical species, such as white-nosed coati and javelina are greater than in adjacent areas of Arizona. Human presence is less evident than in southeastern Arizona. On the other hand, relative abundance of black bear (Ursus americanus) is less than in southeastern Arizona and some ranges in northeastern Sonora. Many camera trap projects are short-term, often to assess density without violating assumptions of deaths, births, immigration, and emigration; however, we found large seasonal and yearly variations in relative abundance of some species that paints a cautionary tale for researchers. Short- term studies can create a snapshot in time that may not represent longer-term averages or variation. Rancho El Aribabi is a conservation ranch designated as a private Protected Natural Area by the Mexican government. This designation and careful management of the property by the owners, the Robles family, create a safe environment for the mammals of the area. However, re-routing of Mexican Highway 2 through the ranch would fragment habitat and isolate some mammal populations, including that of the ocelot. The effects of climate change may eliminate seasonally important waters in the Sierra Azul and alter vegetation communities. Monitoring these changes within the context of our baseline work and the work of others at Rancho El Aribabi could yield findings important for future conservation actions in the sky island region.