Spatial Ecology of Sonoran Desert Tortoises (Gopherus morafkai): I. Fidelity in Home Range, Refuge Use and Foraging Behavior

The behavioral ecology of Sonoran Desert Tortoises (Gopherus morafkai) remains relatively unstudied. In general, Sonoran Desert Tortoises (SDTs) differentially use incised washes and rocky slopes and avoid open flats and intermountain valleys, except during apparent emigration events. We know relatively little about the temporal pattern of space use in SDTs and even less about such use in relation to sex. We observed activity of adult and juvenile SDTs via radiotelemetry, and hatchling activity incidentally, over a 3-yr period in central Arizona. The SDTs were most active in the fall (August-October) but exhibited a second peak of activity in the spring (April). On average, males moved longer distances than did females in every month of the year when SDTs were active. Distance moved by females in the fall was significantly greater than all other months except April; a similar pattern of greater male movement in the fall was apparent but not statistically significant. Activity of adults was detected in virtually every month of the year except January; at least one hatchling was observed active in every month of the year. We conclude that adult SDTs home range areas 1) are consistent in size and placement across multiple years and, for females especially, may include a "migratory" pattern to north slopes following summer rains, where they encounter a higher diversity and abundance of food plants; 2) are highly overlapping in females but less so in males; and 3) contain a few refuges in relatively lower elevation washes that are used consistently, especially during the hot, dry summer (May and June), and that are selected over many other available caliche refuges.