Confirmation of the presence of Abert’s squirrel (Sciurus aberti) after a century in Sonora, México

Abstract

According to several authors, Abert’s squirrel (Sciurus aberti) is typically found in ponderosa pine (Pinus ponderosa) forest, which provides both shelter and food.  Pinus ponderosa generally occurs between 1,800 and 3,000 m elevation in Wyoming, Colorado, New Mexico, Arizona, and Utah in the United States.  In México, Pinus arizonica was formerly considered a variety of P. ponderosa in northern Sonora.  Conifer forests in the Sierra Madre Occidental from southern Durango north to Sonora and Chihuahua are not monospecific but very diverse.  Pine-oak forest is dominated by various species of pines and oaks, and mixed conifer forest by Douglas fir (Pseudotsuga spp.), spruce (Picea sp.), and southwestern white pine (Pinus strobiformis).  There is a previously confirmed record of Abert’s squirrel from the Upper Bavispe River, Sonora, collected by the Lumnholtz Archeological Expedition 1890-92, and another unconfirmed record of a likely Sciurus aberti in 1938 in northern Sonora.  While conducting mammal surveys on foot (recording tracks of different mammals) and setting up camera traps, we observed the presence of S. aberti in the study area.  We obtained two photographic records of S. aberti, in pine-oak forest in the Sierra Madre Occidental at the town limit of Mesa Tres Ríos, and at 9.4 km southwest of Mesa Tres Ríos, Sonora.  Sciurus aberti were found on areas with pine-oak and mixed-conifer forests, presumably used for food and cover by Abert’s squirrels, demonstrating that these squirrels are not strictly dependent on ponderosa pine (P. ponderosa) as previously reported, instead they rely on oak, Arizona (P. arizonica) and Apache (P. engelmannii) pines, that are widespread in the Madrean Archipelago (Sky Islands Region) and the northern Sierra Madre Occidental (SMO).  These observations confirm the predictions of the presence of S. aberti and are an important addition to the mammal fauna of Sonora.