Space Use by Free-ranging, Juvenile Sonoran Desert Tortoises (Gopherus morafkai) in Central Arizona, USA

Spatial ecology of very young (≤ 3 y of age) desert tortoises in the American Southwest remains little known, especially for Sonoran Desert Tortoises (Gopherus morafkai). From 2013-2021 at a field site in upland Sonoran Desert in central Arizona, USA, we observed 13 juvenile G. morafkai for an average of 9 mo each. Based on size and carapace characteristics, we estimated that most of our subjects were in their first-or second-year post-hatching (median straight line carapace length = 50 mm; range, 44–62 mm; n = 13). Relative to adults, these very young tortoises occupied extremely small home ranges: as estimated by Minimum Convex Polygons, they ranged from 0.002 to 0.055 ha, but the median was only 0.007 ha (= 70 m²). Young tortoises were active in every month of the year, but especially February, March, and April (75% of all sightings) and 88% of feeding events occurred during March and April. Mean daily speed, an estimate of movement within months, was significantly higher in late winter and early spring relative to the remainder of the year. There was no relationship between home range size and either tortoise size or duration of observation (months), or number of resightings. Rainfall stimulated activity, but we observed many individuals basking during the winter, even in cold, dry weather. Like adults, some individuals switched back and forth between refuges, which were typically small burrows at the bases of shrubs either self-made or co-opted from rodents.