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Dynamic occupancy modelling to determine the status of a Critically Endangered lizard

Turner, Heléna, Griffiths, Richard A., Outerbridge, Mark E., Garcia, Gerardo (2023) Dynamic occupancy modelling to determine the status of a Critically Endangered lizard. Oryx, 57 (1). pp. 23-29. ISSN 0030-6053. E-ISSN 1365-3008. (doi:10.1017/S0030605321000843) (KAR id:99535)


Monitoring of cryptic or threatened species poses challenges for population assessment and conservation, as imperfect detection gives rise to misleading inferences about population status. We used a dynamic occupancy model that explicitly accounted for occupancy, colonization, local extinction and detectability to assess the status of the endemic Critically Endangered Bermuda skink Plestiodon longirostris. During 2015–2017, skinks were detected at 13 of 40 surveyed sites in Bermuda, two of which were new records. Ten observation-level and site-specific covariates were used to explore drivers of occupancy, colonization, extinction and detectability. Sites occupied by skinks tended to be islands with rocky coastal habitat and prickly pear cacti; the same variables were also associated with reduced risk of local extinction. The presence of seabirds appeared to encourage colonization, whereas the presence of cats had the opposite effect. The probability of detection was p = 0.45, and on average, five surveys were needed to reliably detect the presence of skinks with 95% certainty. However, skinks were unlikely to be detected on sites with cat and rat predators. Dynamic occupancy models can be used to elucidate drivers of occupancy dynamics, which in turn can inform species conservation management. The survey effort needed to determine population changes over time can be derived from estimates of detectability.

Item Type: Article
DOI/Identification number: 10.1017/S0030605321000843
Uncontrolled keywords: Bermuda skink; conservation; dynamic occupancy modelling; Plestiodon longirostris; population monitoring; reptile
Subjects: Q Science > QH Natural history > QH541 Ecology
Q Science > QH Natural history > QH75 Conservation (Biology)
Divisions: Divisions > Division of Human and Social Sciences > School of Anthropology and Conservation > DICE (Durrell Institute of Conservation and Ecology)
Funders: Chester Zoo (
British Herpetological Society (
Depositing User: Richard Griffiths
Date Deposited: 16 Jan 2023 09:37 UTC
Last Modified: 04 Mar 2024 17:06 UTC
Resource URI: (The current URI for this page, for reference purposes)

University of Kent Author Information

Griffiths, Richard A..

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