Ecology of the desert tortoise (Gopherus agassizii) in a desert-grassland community in southern Arizona

Abstract

After 6-10 years of mark-recapture observations, I studied seven desert tortoises by radio-telemetry during 1990-1992 in a desert-grassland community in Pinal County, Arizona. Six estimated home-range areas averaged 14.7 ha. Winter-spring (Nov-Jun) use areas (overline x=0.7 ha) were significantly smaller (P = 0.002) than summer-fall (Jul-Oct) use areas (overline x=10.7 ha). A correction formula inflated 1-2 summer-fall use areas of five tortoises 4-41% larger than their corrected home-range areas. Extended movements by females were significantly more frequent (P = 0.0001) than those of males during Mar-Jul, significantly less frequent (P = 0.0057) than males during Aug-Oct, and most frequent by both sexes in September. Use of two slopes and terraces was not season-dependent (P = 0.9159). Tortoises variably used four shelter types (rock, soil burrow, wood rat nest, vegetation), significantly with south-facing entrance aspects (P 0.0005). Hibernaculum structure and location varied. Hibernation ranged from 88-315 days. Radio-equipped tortoises included reuse of mark-recapture locations.