Update on the Natural History and Conservation Status of the Saint Lucia Racer, Erythrolamprus Ornatus Garman, 1887 (Squamata: Dipsadidae)

Herpetology Notes, volume 9: 157-162 (2016) (published online on 01 August 2016) Update on the natural history and conservation status of the Saint Lucia racer, Erythrolamprus ornatus Garman, 1887 (Squamata: Dipsadidae) Robert J. Williams1,*, Toby N. Ross1, Matthew N. Morton1, Jennifer C, Daltry2 and Lenn Isidore2, 3 Abstract. The ground snake Erythrolamprus ornatus is a dipsadid endemic to Saint Lucia, West Indies; it was first categorized as Endangered on the IUCN Red List in 1996. There have been no sightings of the snake on the main island of Saint Lucia since the 1800s, and although the species is believed to have once been common on Saint Lucia prior to the introduction of the small Indian mongoose (Herpestes javanicus), by 1936 the species was presumed extinct. In 1973, a single E. ornatus was found on the mongoose free, 9.4 ha (12.3 ha surface area) islet of Maria Major, less than 1 km off the southern tip of Saint Lucia. All subsequent accounts of the species have been from Maria Major alone. Here we report the findings of the first detailed study of the population size, diet, and ecology of the Saint Lucia racer, which took place on Maria Major over 30 days between October 2011 and March 2012. Daylight searches produced a total of 41 snake encounters resulting in capture of 11 individuals. A Capture Mark Recapture (CMR) estimate of population size suggests there are fewer than 50 mature individuals on Maria Major. We therefore propose a revised classification of Critically Endangered. Erythrolamprus ornatus on Maria Major appear to be smaller and less colourful than individuals once described from the main island of Saint Lucia, possibly the effects of a genetic bottleneck in this isolated population. Keywords. Erythrolamprus ornatus, Saint Lucia, natural history, conservation. Introduction other predators onto many Lesser Antillean islands is inferred to have been the primary cause of population The 30 endemic snakes of the Lesser Antilles (Eastern declines and extinctions (Henderson, 2004; Powell and Caribbean) are of great conservation interest and concern. Henderson, 2005). Although the distribution of snakes With most species having restricted ranges, this group throughout the region is well documented (Schwartz has proved to be highly prone to island extirpations and and Henderson, 1991; Henderson, 2004; Powell and extinctions (Henderson, 2004; Henderson and Powell, Henderson, 2005), an understanding of the population 2009; Caut and Jowers, 2015). The introduction of status and ecology is lacking for many species, the small Asian mongoose (Herpestes javanicus) and particularly those that are very rare and in need of conservation management (with the notable exception of Alsophis antiguae, see Daltry et al., 2001). Due to limited data from very few documented captures, little is known of the ecology and population 1 Durrell Wildlife Conservation Trust, c/o Forests and Lands status of the Saint Lucia racer (Erythrolamprus ornatus; Resources Department, Gabriel Charles Forestry Complex, Fig. 1). In his early notes on the snakes of Saint Lucia, Union, Castries, Saint Lucia, West Indies Tyler (1850) described the ‘couresse’ as a small snake 2 Fauna & Flora International, The David Attenborough of 2.5–3 feet [76–91 cm] in length, which was the first Building, Pembroke Street, Cambridge CB2 3QZ, United literature reference to E. ornatus. Although no mention Kingdom 3 Forests and Lands Resources Department, Gabriel Charles was given of its distribution, Tyler (1850) recorded Forestry Complex, Union, Castries, Saint Lucia, West Indies that the couresse was the second-most common of the * Corresponding author. E-mail: [email protected] five extant snake species on Saint Lucia at that time, 158 Robert J. Williams et al. to quantify the population’s size, rate of population change, and threats to the species, application of criteria for a listing as Critically Endangered was not justified (Richard Gibson, pers. comm.). The need to review the conservation status of the Saint Lucia racer was recognized by Daltry (2009) and Morton (2009), whose appraisal of the threats faced by this precarious, isolated population included invasive predators, climate change, inbreeding depression, and stochastic events. Both authors argued strongly for an updated assessment and a listing as Critically Endangered. The need for a revised assessment of the status of the Saint Lucia racer, Figure 1. The Saint Lucia racer (Erythrolamprus ornatus) and the development of a species action plan, was also Photograph by Toby Ross. identified in the management plan of the Pointe Sable Environmental Protection Area (PSEPA) (Gardner, 2009), the largely marine protected area that includes the Maria islands. Here we report the findings of the first detailed study of the population size and ecology of the Saint Lucia strongly suggesting it was widespread throughout the racer, which took place on Maria Major (13.4327°N, island 19 years prior to the introduction of mongooses 60.5553°W) between October 2011 and March 2012. to Saint Lucia (Des Voeux, 1903). The species was believed to be extinct by 1936 (Parker, 1936; Honegger, Materials and Methods 1981), and there have been no recorded sightings on the main island of Saint Lucia since the 1800s. In 1973, We adapted methods from those used to estimate the a single E. ornatus was found on the 9.4 ha (12.3 ha number of Antiguan racers on the offshore islands of surface area) islet of Maria Major, less than 1 km off Antigua (Daltry et al., 2003). We employed daylight the southern tip of Saint Lucia (Geoghegan and Renard, visual searches for snakes amounting to a total of 644 1985). All subsequent observations of the species have man hours over 30 days. Our survey team, consisting been from Maria Major alone (Corke, 1987; Sherriff et of up to six surveyors, repeatedly walked a series of al., 1995; Buley et al.,1997; Morton, 2009). One other nine trails of varying length (Fig. 3) that facilitated snake species is known to occur on Maria Major, the unhindered movement throughout the island (most diminutive Saint Lucia threadsnake (Tetracheilostoma breuili) (Daltry, 2009). There is limited information available on the diet of E. ornatus, apart from the second-hand sighting reported in Sherriff et al. (1995) of an individual eating an adult Saint Lucia anole (Anolis luciae). Tyler (1850) listed lizards, anurans, mice, and other small animals as the prey taken when the snake was prevalent on the Saint Lucia mainland. In the absence of mammals and amphibians on Maria Major, A. luciae, and the Saint Lucia whiptail (Cnemidophorus vanzoi), were suggested to be the main prey items (Corke, 1987; Sherriff et al., 1995; Henderson, 2004; Morton, 2009). The Saint Lucia racer population was evaluated and listed as Endangered by Gibson (1996). It seems the assessor considered that the entire world population, found only on the 12 ha, mongoose- and rat-free, nature reserve of Maria Major (Fig. 2), comprised no Figure 2. Maria Major Island (foreground), Saint Lucia, West more than 250 mature individuals. With a lack of data Indies. Photograph by Toby Ross. Update on the natural history and conservation status of the Saint Lucia racer 159 diet, each captured individual’s intestinal tract was gently palpated to attempt to extract a faecal sample to examine for the presence of prey remains. Capture-mark-recapture (CMR) data were analysed using Begon’s weighted mean estimator (Begon, 1979) to estimate the number of adults and subadults in the population after determining that all assumptions of the model had probably been met (e.g., the island population is geographically closed and not subject to immigration or emigration, demographically closed for the duration of the study with no presumed deaths and no juveniles included in the estimate, and that all individuals are equally likely to be caught; Daltry et al., 2001). Because previously caught animals can remain at the point of release for some time and become biased to recapture (Daltry et al., 2012), we also excluded snakes caught less than 48 h since previous capture from the estimate. Results Actively searching for snakes during daylight hours produced a total of 41 snake encounters, 16 of which were captured. Of the 16 captures, five were recaptures, Figure 3. Maria Major Island with survey trails detailed to thus a total of 11 individuals were captured. One of indicate areas searched. these recaptures was omitted from the population size analysis below because it occurred less than 48 hrs after initial capture. The mean encounter rate for the survey team was 41 in 301 h (0.14 snakes/h), and the mean encounter rate for each member of the survey team was 41 in 644 h (0.06 snakes/man-hour). of the trails were created in advance of the study, to When applied to our CMR data, Begon’s weighted facilitate access to areas that were previously difficult mean method estimated a population size of 17.8 to reach). All trails were surveyed multiple times over adult and subadults, with a standard error of ± 9.94. the course of each survey day (0800–1700 h). Attempts As we made only three recaptures (one individual was were made to capture by hand all snakes encountered. recaptured on two occasions), this estimate should be Upon capture, snakes were sexed and measurements treated with caution. made of snout–vent length (SVL), tail length, and total Morphometric measurements and scale counts were length (TL) using string, as well as head length and head recorded from 11 individual Saint Lucia racers (Table width using dial callipers following methods outlined 1). The largest of the 11 individuals captured had a in Daltry (2002). Counts of ventral and subcaudal total body length of 775 mm. The mass of the captured scales were also made.

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