Natural History of Sonoran Desert Tortoises: Ten Years on the Urban Fringe (2021-03-12)

Abstract

The spatial and behavioral ecology of a population of Sonoran Desert Tortoises (= SDTs; Gopherus morafkai) was documented over a ten year period (2010-2020). The study population occupied the eastern slopes and washes of the southern Union Hills on the northeast edge of the Phoenix Metropolitan Region. Consequently, it has experienced a long history of anthropogenic impacts, including mining, grazing, off-road vehicle activity, and dam construction. We used radio-telemetry to intensively track 10-25 adult SDTs each year (ave = 100 relocations for each individual annually) from 2010 through 2021. Hatchling tortoises (1-3 yrs of age, < 60 mm in length) were too small to be radio-tagged but were monitored haphazardly. We documented relatively little variation in home range size and location across years for both male and female SDTs. During years with at least average summer rainfall (~75 mm or more), females moved to slightly higher elevation north-facing slopes to feed; males did not exhibit a similar shift in activity. We assessed anthropogenic impacts and their possible mitigation by use of short-distance translocation. Small sample size precludes robust conclusions, but our results are consistent with prior work suggesting SDTs are not good candidates for mitigation translocation. Behavioral adaptations suggest that increasing temperatures due to climate change will be less significant for this population than a descrease in rainfall. Any reduction in rainfall will be especially problematic for hatchlings.