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27th Annual Meeting and Symposium of the
Desert Tortoise Council, March 22-24, 2002
Abstracts
Characteristics of Winter Hibernacula Used by Recently Released Neonate and Juvenile Desert Tortoises at Fort Irwin
Lisa C. Hazard1,2 and David J. Morafka3
1Department of Organismic Biology, Ecology and
Evolution, University of California, Los Angeles, CA 90095-1606;
2Present address: Department of Ecology and
Evolutionary Biology, Earth and Marine Sciences Building A308,
University of California, Santa Cruz, CA 95064;
3Department of Biology, California State University,
Dominguez Hills, Carson, CA 90747-0005
Behavior of young tortoises released from semi-natural hatcheries could be affected by the age of the tortoise or by the length of time spent within the hatchery before release. Juvenile (6-8 years old) and neonate (< 2 months old) desert tortoises (12 per group) were fitted with radiotransmitters and released from the hatchery at the Fort Irwin Study Site (National Training Center, Fort Irwin, CA) in October 1999, and their movements were tracked until all stopped moving (presumably hibernating) and no activity was observed, 34 days later. Juvenile and neonate tortoises exhibited differences in dispersal behaviors; neonates selected a hibernation burrow more quickly. To test whether age classes differed in burrow selectivity, we measured characteristics of hibernation burrows and neighboring burrows (in February, after the animals had vacated the burrows). Juvenile tortoises used larger burrows than neonates, but within age class there was no correlation between tortoise size and burrow size. The burrows of neonates were not oriented in any particular direction, whereas juvenile burrow orientation did differ significantly from a uniform distribution, with a mean direction of 149° (SSE). The selectivity of juveniles compared to neonates may have resulted in more movement by the juveniles (longer time to select a hibernation burrow and more sites occupied per individual before hibernation). This increased movement could result in higher exposure to predation risk, though there was no mortality in either group in this study.