Red bellied racer

A population assessment and habitat description of the Alsophis rufiventris on the Quill and Boven National Park, St. Eustatius

The genus Alsophis used to be very abundant in the Lesser Antilles. Numbers have declined ascribed to anthropogenic causes and the introduction of invasive species to their habitat. Most Alsophis species are classified as endangered or critically endangered by the IUCN. Alsophis rufiventris, a species native to the islands Saba and St. Eustatius, is facing a constant threat of the Javan mongoose being introduced in its habitat. Also dogs, cats, rats and humans actively influence the abundance of A. rufiventris. Though all these threats, the population of A. rufiventris seemed stable and was classified as vulnerable by the IUCN in 2016. In 2017 hurricane Irma and Maria impacted on Saba and St. Eustatius. It was expected that the A. rufiventris population was altered. Therefore a new population assessment was done in the Quill and Boven National Park on St. Eustatius in 2018 and was repeated in this study. In 2018 the population size in the study area was 165.

Distance sampling with line transects was used to estimate the population size of A. rufiventris. In this study 1068 line transect surveys resulted in 60 snakes recordings. As the snake count was sparse, N-mixture models were used as well.

Distance sampling resulted in a population size of 464 and the N-mixture models resulted in a population size of 178. These results are preliminary, as covariates had no influence on the model in the program DISTANCE. While, according to earlier research by Savit et al. in 2015 the covariates should influence the results. Multipliers have to be added in the program DISTANCE to get more accurate results. From this study the habitat preference of A. rufiventris cannot be described, as the findings on habitat categories were not significantly different from each other.

A. rufiventris is becoming more rare in its native habitat and that is a cause for concern. As many threats to the species are present, but also actively influence their abundance, the species might become, or effectively already can be categorized as (critically) endangered. It is advised to continue monitoring of this species not only on St. Eustatius but on Saba as well. Also conservation actions like establishing biosecurity and conducting rodent control might be beneficial. As these conservation actions might not happen in the near future, a breeding program in a zoo might be beneficial to preserve the genetic variance in the population.

Date
2019
Data type
Research report
Theme
Research and monitoring
Geographic location
St. Eustatius
Author
Image
Red bellied racer

Raw data of snake surveys on St.Eustatius

Raw observation data of the Red bellied racer on St.Eustatius from 2017-2018, including: location, length, elevation and weather conditions.

Please contact Hannah Madden for more information.

Date
2018
Data type
Raw data
Theme
Research and monitoring
Geographic location
St. Eustatius

The Distribution and Dispersion of the Alsophis rufiventris on the Quill, Sint Eustatius

The Lesser Antilles are home to four different colubrid snakes of the Alsophis genus. Alsophis used to be common around the Lesser Antilles, but has declined dramatically. The Red-bellied Racer snake (Alsophis rufiventris) is one of those four endemic Alsophis species of the Lesser Antilles. The islands St. Eustatius (Statia), Saba, St. Kitts and Nevis used to be home to A. rufiventris, when in the 1900s A. rufiventris got extirpated on St. Kitts and Nevis. Only two subpopulations exist today, on 10.9% of its original range. Therefore, A. rufiventris is now classified as endangered on the IUCN red list. A better understanding of these animals can help in effectively protecting them. To get an idea of the distribution and dispersion on the trails of the western slope of the Quill was investigated, because the abundancy of A rufiventris was thought to be the highest there.

In total 66 snakes were PIT tagged, over a three month period, of which 34 males and 32 females, suggesting a sex ratio of 50:50. Every snake was measured to see if there was a difference in tail length between males and females, to create an easy, costless and harmless way to distinguish both sexes, other than from the look of the exterior. Males had a significant longer tail, making it possible to use this method to identify the sexes.

Encounters and reencounters were mapped to give an idea about the dispersion of A. rufiventris. There were 43 reencounters, of which 4 snakes where reencountered three times after initial tagging. Different snakes were reencountered several times within a 80 meter range. Only one snake was reencountered about a kilometre from the first three encounters of that individual. Therefore, over this short period A. rufiventris seemed to have a certain home range, though the behaviour of other Alsophis species suggest that they will be rather nomadic over a longer time period. For that reason, long time study is suggested, to learn more about the specific behaviour of this species.

[Student report]

Date
2017
Data type
Research report
Theme
Research and monitoring
Geographic location
St. Eustatius
Author