Assessing Abundance of a Cryptic Viper Using N-Mixture Models

Dreslik, Michael J.

Illinois Natural History Survey

Prairie Research Institute

University of Illinois Urbana-Champaign

Champaign, Illinois, USA

Crawford, John A.

National Great Rivers Research and Education Center

Alton, Illinois, USA

Baker, Sarah J.

Arizona Game and Fish Department

Phoenix, Arizona, USA

For effective conservation and recovery, an adaptive management framework is often best when paired with monitoring population-level responses. In many species, monitoring abundances over time using traditional capture-mark-recapture (CMR) methods is logistically challenging. N-mixture models are an extension of the occupancy and detection probability framework and can estimate abundances across multiple populations. The models use raw abundance counts taken during surveys, model the distributions of capture frequencies, incorporate density-dependent effects, and can provide population estimates when recaptures are too few. When validated with traditional CMR estimates, they can provide robust estimates for multiple populations across the landscape. We chose to determine the effectiveness of an N-mixture modeling approach to generate population size estimates for the Eastern Massasaugas within the Carlyle Lake region in Illinois. Our results will be used to determine regional population trends and provide a foundation to assess the effectiveness of conservation actions.

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