A population model of the impact of a rodenticide containing strychnine on Great Basin Gophersnakes (Pituophis catenifer deserticola)

Abstract

Strychnine is a neurotoxin and an active ingredient in some rodenticides which are placed in burrows to suppress pocket gopher (Thomomys talpoides) populations in range and crop land in western North America. The population level impact was modelled of the use of strychnine-based rodenticides on a non-target snake species, the Great Basin Gophersnake (Pituophis catenifer deserticola), which is a predator of pocket gopher and a Species at Risk in Canada. Using information on population density, demographics, and movement and habitat suitability for the Gophersnake living in an agricultural valley in BC, Canada, we estimated the impact of the poisoning of adult snakes on the long-term population size. To determine the area where Gophersnakes could be exposed to strychnine, we used vendor records of a rodenticide, and quantified the landcover areas of orchards and vineyards where the compound was most commonly applied. GIS analysis determined the areas of overlap between those agricultural lands and suitable habitats used by Gophersnakes. Stage-based population matrix models revealed that in a low density (0.1/ha) population scenario, a diet of one pocket gopher per year wherein 10 % of them carried enough strychnine to kill an adult snake could cause the loss of 2 females annually from the population and this would reduce the population by 35.3 % in 25 years. Under the same dietary exposure, up to 35 females could die per year in a high density (0.4/ha) population which would result in a loss of 50 % of adults in 25 years.

Intensive livestock farming as a major determinant of the exposure to anticoagulant rodenticides in raptors of the Canary Islands (Spain)

“…The pattern exposure to ARs in the Canary Islands is mainly linked to the intentionality in poisonings, which coincides with what has been also described in this archipelago for other pesticides (Ruiz-Suarez et al, 2015), and for other non-anticoagulant rodenticides elsewhere (Bishop et al, 2016). However, this pattern differs considerably from that described by other authors for reptiles (Elliott et al, 2014;Johnston et al, 2005;Nakayama et al, 2019) and mammals (Alabau et al, 2020;Nakayama et al, 2019), and moreover, from the main objective of this work that focuses on secondary exposure, we decided to discard the specimens of these two classes, as well as the baits, for further analyses in this research.…”

Using Ecological Niche Models for Population and Range Estimates of a Threatened Snake Species (Crotalus oreganus) in Canada

“…While pesticide exposure (through bio-accumulation in prey items) and interactions with humans or machines can pose risks for snakes [65], agricultural landscapes also often harbor food resources, access to water and relatively stable vegetation types (e.g., orchards or pasture). We therefore included several agricultural land cover types in our models-including intensively-farmed cropland (comprised of cultivated crops, fallow land, transitional cropland), vineyards and berries (combined) and perennial agricultural land of ecological value known to be used by rattlesnakes (orchards-fruit trees; see Table S1).…”

“…Here, we address these issues by combining observational data with climate and land cover GIS layers to quantify the area of habitat that could be used by western rattlesnakes throughout BC, with density estimates from capture-mark-recapture (CMR) studies on western rattlesnake populations [28,63]. Because we know that snakes are vulnerable to the impact of roads [64] and bio-accumulation of pesticides within the study area [65] we also examined the proportion of land cover suitable for western rattlesnakes that occurs within and outside the following designations: protected areas, a road buffer and agricultural land. Our specific goals were to determine: (1) the first approximate estimate of available habitat and population size for the western rattlesnake in BC based on observational data, and use supporting estimates from den counts to determine a threshold of occurrence; (2) the effects of different land cover and topographical variables on presence of western rattlesnakes; and different scenarios-including or excluding protected areas, roads and a 500 m buffer, and agricultural land-on models of the BC population estimate.…”