Wildlife Camera Observations, Mammal Assemblage and Seasonal Dynamics at Tinajas in Two Sonoran Desert Natural Reserves

Abstract

In the Sonoran Desert, permanent surface water is rare; ephemeral and isolated waters are often the primary sources for many wildlife species. Rock pools known as tinajas are one of these water sources and are utilized by a wide variety of mammals, birds and other wildlife. Tinaja hydroperiod (duration of water) is entirely driven by rainfall and climatic changes could endanger their viability as seasonal water sources in the future. Employing wildlife cameras, we examined wildlife use over a two-year period (2019-2021) in two protected areas of the western Sonoran Desert: Organ Pipe Cactus National Monument (OPCNM) and the Pinacate Biosphere Reserve (PBR). Our objective was to establish a baseline for species richness and mammal assemblage at these tinajas, understand how hydroperiod affects overall species richness and gain broad insight about wildlife seasonal dynamics. In total we made 11,678 wildlife observations across the entire study. We observed 20 species of mammals across all 12 study tinajas in both reserves. We made incidental observations of 42 bird species and 2 amphibian and reptile species across both reserves. There was a significant difference in the mean mammal species richness between the two parks (T= 2.93, p = 0.015) with OPCNM having greater richness, likely due to the presence of montane habitat. The average number of mammal species observed at tinajas in OPCNM was 11.16 with SD = 2.6. For PBR, the average number of species was 6.8 with a SD = 2.5. We found a visual trend of higher species richness being observed at smaller tinajas and lower richness at large tinajas (>100m2) but did not have a large enough sample size to conduct a statistical test. We did not find a significant linear relationship between hydroperiod of the tinajas and mammal species richness. Mammal assemblage composition differed significantly between the two reserves (p < 0.001). Six taxa were significant indicators for tinajas at Organ Pipe, including rodents, bats, spotted skunk (Spilogale gracilis), and puma (Puma concolor), but only coyotes (Canis latrans) were significant indicators for tinajas at Pinacate. We make note of the most common mammal species for each reserve and visually notable patterns in seasonal ecology. Gray fox (Urocyon cinereoargenteus) and coyote (PBR). At one site we observed that bighorn sheep (Ovis candensis) tended to be absent during times that honeybees (Apis mellifera) were present. By quantifying wildlife observations at these sites, we hope to provide a baseline to establish the importance of tinajas in supporting the unusually high wildlife species richness of this arid region. Global climate change has the potential to drastically alter the regions rain cycle so understanding the dynamics of which wildlife utilize tinajas can help better inform future management decisions and studies.