Ward, Robert J., Griffiths, Richard A., Wilkinson, John W., Cornish, Nina (2017) Optimising monitoring efforts for secretive snakes: a comparison of occupancy and N-mixture models for assessment of population status. Scientific Reports, 7 . ISSN 2045-2322. (doi:10.1038/s41598-017-18343-5) (KAR id:65571)
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Official URL http://dx.doi.org/10.1038/s41598-017-18343-5 |
Abstract
A fifth of reptiles are Data Deficient; many due to unknown population status. Monitoring snake populations can be demanding due to crypsis and low population densities, with insufficient recaptures for abundance estimation via Capture-Mark-Recapture. Alternatively, binomial N-mixture models enable abundance estimation from count data without individual identification, but have rarely been successfully applied to snake populations. We evaluated the suitability of occupancy and N-mixture methods for monitoring an insular population of grass snakes (Natrix helvetica) and considered covariates influencing detection, occupancy and abundance within remaining habitat. Snakes were elusive, with detectability increasing with survey effort (mean: 0.33 ± 0.06 s.e.m.). The probability of a transect being occupied was moderate (mean per kilometre: 0.44 ± 0.19 s.e.m.) and increased with transect length. Abundance estimates indicate a small threatened population associated to our transects (mean: 39, 95% CI: 20–169). Power analysis indicated that the survey effort required to detect occupancy declines would be prohibitive. Occupancy models fitted well, whereas N-mixture models showed poor fit, provided little extra information over occupancy models and were at greater risk of closure violation. Therefore we suggest occupancy models are more appropriate for monitoring snakes and other elusive species, but that population trends may go undetected.
Item Type: | Article |
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DOI/Identification number: | 10.1038/s41598-017-18343-5 |
Projects: | [UNSPECIFIED] Status and conservation of the grass snake in Jersey |
Uncontrolled keywords: | occupancy, snake, abundance, monitoring, dataset, Natrix helvetica, Jersey, N-mixture, detection |
Subjects: |
Q Science > QH Natural history > QH301 Biology Q Science > QH Natural history > QH541 Ecology Q Science > QH Natural history > QH75 Conservation (Biology) Q Science > QL Zoology |
Divisions: |
Divisions > Division of Human and Social Sciences > School of Anthropology and Conservation Divisions > Division of Human and Social Sciences > School of Anthropology and Conservation > DICE (Durrell Institute of Conservation and Ecology) |
Depositing User: | R.J. Ward |
Date Deposited: | 27 Dec 2017 17:24 UTC |
Last Modified: | 16 Feb 2021 13:52 UTC |
Resource URI: | https://kar.kent.ac.uk/id/eprint/65571 (The current URI for this page, for reference purposes) |
Ward, Robert J.: | ![]() |
Griffiths, Richard A.: | ![]() |
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