Home range and habitat of the desert tortoise (Xerobates agassizi) in the Picacho Mountains of Arizona

Home range and seasonal habitat use of 14 desert tortoises (Xerobates agassizi) were monitored from April 1982 to September 1983 in the Picacho Mountains of Arizona. Tortoises limited their home range movements to the palo verde-cacti-mixed scrub vegetation on rocky slopes, bajadas, and associated washes. Average home range size for all monitored tortoises was 19 ha (range 3-53 ha). Home range size was not significantly different between sexes and was not correlated with carapace length or number of observations. Tortoises used an average of eight dens each and reused previously occupied dens. Tortoises occupied larger dens in summer than in other seasons and moved to steeper rocky slopes in winter. Habitat use in the Picacho Mountains corroborated that previously reported for the Sonoran Desert but differed greatly from that reported for the Mohave Desert. Moreover, habitat use differences between the two deserts complement the geographic trends observed in mitochondrial DNA and morphometric surveys of these regions.