HOME RANGE AND MOVEMENT PATTERNS OF THE BOLSON TORTOISE, GOPHBRUS FLAVOMARGINATUS

Abstract

A colony of G. flavomarginatvs was studied during two consecutivo summers at the Mapimi Biosphere Reserve, Durango, México. Movements and behavior of individuáis living in a 77 ha area were recorded by means of radiotelemetry. Objectives of this study were to determine home range and movement patterns, and to evalúate these using probabilistic (Jenn- rich and Turner, 1969; Calhoun and Casby, 1958; Koeppl et al, 1975, and a variant of this model named 68% bivariant ellipse) and non*probabilistic mo- dels (Harvey and Barbour, 1965 and mínimum convex polygon). According to direct observation of movements in the field, home rangos are not overesti- mated only by the mínimum modified polygon and the 68% bivariant ellipse, respectively: 3.1 and 4.1 ha for adult males; 2.5 and 3.1 ha for adult females, and 0.4 and 1.2 ha for immature individuáis. Correlation valúes (r) of carapace lengíh vs. home range area and severa! motility measures vary from 0.54 to 0.85. Sixty four percent of tortoises in the colony use one or two burrows, and 36% use four to eighí burrows. An analysis by the Poisson distribution showed aggregation for both burrow dispersión (t = 3.66 p < 0.05) and activity center (t = 5.20 p < 0.05) patterns. These data suggest definite ecological and be- havioral relationships within the contexí of a social hierarchy system.