Project: Habitat quality and demographic performance of desert tortoises located in Mojave National Preserve

 


Introduction:

Agassiz's desert tortoise (Gopherus agassizii) is an endemic to the Southwestern deserts of North America. In spite of being a focus of research for over 20 years relatively little is known about the habitat requirements necessary for stable population growth rates. Individuals are highly cryptic and spend the majority of their time in subterranean burrows. They primarily forage on annual plants that have short activity seasons usually lasting a few weeks. The combination of these and other factors has made it difficult to study movement, behavior, and resource selection by the desert tortoise.

Objective:

Identify habitat and resource variables that correlate highly to demographic performance, measured through reproductive effort (egg production and hatchling body condition) and adult and juvenile size and body condition. Use selected variables to develop parameters that may be used to predict high quality habitat areas throughout the species distribution for both adult and juvenile animals.

Methods:

Adult females are equipped with radio transmitters and located regularly. Habitat and resource measurements are conducted within each females homerange for statistical analysis. Females are X-rayed periodically during their reproductive season, and gravid individuals are brought to pens located at Ivanpah Desert Tortoise Research Facility (IDTRF). Post-nesting in predator excluded pens females are returned to their capture location, and eggs are left to incubate naturally. Twenty hatchlings are equipped with radio transmitters annually and released into selected habitat classification types and monitored.

Progress:

In 2011 habitat classification types were selected and females were identified and equipped with radio transmitters in each area. Gravid females were brought to IDTRF to nest, and released after nesting had occurred. Hatchling tortoises emerged from nests with a 92% success rate.

Personnel:

Melia Nafus
Graduate Student, Ecology
University of California, Davis

Brian Todd, PhD
Department of Wildlife, Fish, and Conservation Biology
University of California, Davis

Kurt Buhlman, PhD
Savanah River Ecology Lab
University of Georgia

Tracey Tuberville, PhD
Savanah River Ecology Lab
University of Georgia

Funding Sources:

NSF Graduate Research Fellowship; University of California, Davis
California Energy Commission Grant, Public Interest Energy Research Program; University of California, Davis
Jastro-Shields Research Fellowship; University of California, Davis

 

 

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