The Effect of Landscape Change on the Life History of Western Rattlesnakes (Crotalus oreganus)

Background

This project was designed to assess the impact of landscape disturbance on western rattlesnakes by examining trophic interactions among habitat, small mammals, and snakes. The synergistic effect of livestock grazing, invasive plants and fire is changing sagebrush steppe ecosystems in the Upper Snake River Plain. It is hypothesized that this phenomenon is affecting the prey base of top-level predators in the system. The main research goal is to determine if changes in habitat are altering prey availability and subsequently life history characteristics of western rattlesnakes.

Information from this project is important to the DOE for several reasons: (1) as an indicator of how habitat change is influencing small mammal biomass; (2) as an indicator of how trophic interactions affect western rattlesnakes; (3) providing recommendations for the management and conservation of predators on the INEEL; (4) for utilizing a long-term mark recapture data set gathered by the ISU Herpetology Laboratory to further an understanding of community ecology on the INEEL; (5) assisting in the training of graduate and undergraduate students in environmental research.

Objectives

The overall goal of this project is to determine if current landscape patterns in habitat and prey on the INEEL are influencing rattlesnake life histories. Specific objectives for 2004 included the following:

• Quantifying spatial variation in rattlesnake life histories.
• Determine if spatial variation in rattlesnake life histories correlate with coarse scale patterns in habitat and small mammal biomass.
• Determine if rattlesnakes are selecting habitats with greater small-mammal biomass.
• Determine if disturbance to sagebrush steppe systems affects small-mammal biomass.
• Determine if changes in small mammal communities influence body condition of female rattlesnakes.
   

Accomplishments

Specific accomplishments for 2004 include the following:

• Found significant variation in life history characteristics among three den complexes on the INEEL (Table 9-1). More specifically, it was found that snakes at one den complex, Rattlesnake Cave, had life history characteristics that would indicate higher fitness.
• Found that biological soil crust cover; grass cover; and small-mammal species richness, abundance, and biomass were significantly higher and shrub height was significantly lower at Rattlesnake Cave (Table 9-2). Although these results are preliminary, future analyses will examine this issue in greater detail.
• Found that small-mammal biomass was greater in snake core activity areas than in either migration corridors or random locations (Figure 9-1).
• Found that small-mammal biomass was highest in habitats characterized by relatively tall shrub cover, low grass cover, and high biological soil crust cover (Table 9-3).
• Found that average small-mammal biomass within the core area of a rattlesnake's home range had significant influence on the snake's seasonal weight gain (Figure 9-2).

Plans for Continuation

Future plans include placing out a series of data logging stations to monitor the thermal environments available to rattlesnakes (Summer 2005). Specifically, stations will be placed in disturbed and undisturbed sites at both Crater Butte and Rattlesnake Cave. Using the information provided by these stations in combination with small mammal trapping data, a series of potential activity and growth models will be developed. In addition, field and laboratory data collected over the past four years will be analyzed. Analysis of the data set will culminate in a doctoral dissertation (anticipated Spring 2006) and approximately three manuscripts that will be submitted to peer reviewed scientific journals.

Presentations 2004

1. Jenkins, C. L. and C. R. Peterson. Linking landscape disturbance to life history variation among western rattlesnake (Crotalus oreganus) populations. Presented at the Idaho Herpetological Society, Boise, ID.
2. Jenkins, C. L. and C. R. Peterson. Linking landscape disturbance to life history variation among western rattlesnake (Crotalus oreganus) populations. Presented at the Rattlesnake Biology Symposium, Loma Linda, CA.
3. Jenkins, C. L. and C. R. Peterson. Using geostatistical techniques to model the distribution and abundance of amphibians and reptiles. Presented at the Snake Ecology Group Meetings, Carbondale, IL.
4. Jenkins, C. L. and C. R. Peterson. Complementary methods for monitoring amphibian and reptile populations. Presented at the Savannah River Ecology Laboratory (U. S. Department of Energy and University of Georgia).

Investigators and Affiliations

Christopher L. Jenkins , Graduate Student, Herpetology Laboratory, Department of Biological Sciences, Idaho State University, Pocatello, ID

Charles R. Peterson, Professor, Herpetology Laboratory, Department of Biological Sciences, Idaho State University, Pocatello, ID

Funding Sources

Idaho Department of Fish and Game
Bureau of Land Management
Idaho State University (ISU) Department of Biological Sciences
U.S. Department of Energy Idaho Operations Office

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