Habitat suitability and selection of northern pacific rattlesnakes (Crotalus oreganus oreganus) at multiple spatial scales

Graduation Date

2016

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Biology, 2016

Committee Chair Name

Sharyn Marks

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Northern Pacific rattlesnake, Humboldt State University -- Theses -- Biology, Hibernacula, Landslide, Paired resource selection function, Environmental niche model, Crotalus oreganus oreganus

Abstract

Habitat modeling techniques are widely used to determine where species occur on the landscape and what habitat or environmental factors influence their presence. These techniques are particularly useful for rattlesnakes, which have life history traits that make them difficult to study in the field. Additionally, rattlesnakes like the northern Pacific rattlesnake (Crotalus oreganus oreganus) occupy a widespread and diverse range, making their environmental constraints difficult to determine. I used MaxEnt to create an environmental niche model (ENM) at two spatial scales to estimate where the suitable habitat for this species occurs in the Pacific Northwest and, more specifically, in coastal northern California. My results indicate selection for warmer habitats throughout the Pacific Northwest and drier environments within coastal northern California. I also examined the selection of a key aspect of the habitat of C. o. oreganus, the hibernaculum. I used a paired resource selection function to determine microhabitat differences between rocky outcrops used as hibernacula and outcrops that are visually similar, but unoccupied by the rattlesnakes. My top models reveal selection for outcrops with more crevices, fewer cover objects, and slopes facing due south (180° from North) for use as hibernacula. Additionally, temperatures loggers deployed at the hibernacula and their paired sites revealed that hibernacula are consistently warmer, particularly when rattlesnakes emerge in the spring. Lastly, I mapped the landslide activity within the vicinity of the hibernacula, which revealed a positive correlation between landslide presence and hibernacula. Combining these observations with the results of my models paint a comprehensive picture of where the suitable habitat for C. o. oreganus occurs in the Pacific Northwest.

https://scholarworks.calstate.edu/concern/theses/7h149s28x

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