Methods
Summary
Radiotelemetry
Ten snakes will be captured by opportunistic search at night, while Bothrops asper are known to be more active (Sasa et al., 2009). We will select only adults above 250 g of body weight for radiotracking, ensuring the transmitters do not weight more than the 2% of total body mass of the snake. For radiotransmitter implantation we will follow the subdermal stitch attachment method developed by Ciofi & Chelazzi (1991) and modified by Riley, Baxter‐Gilbert, & Litzgus (2017). This method consists to anesthetize locally with bupivacaine (2mg/kg) on the lateral and ventral sides of the tail around the 5th subcaudal scale for females and 16th subcaudal scales for males, for subsequently create an attachment point on both sides of the body by running a subdermal catheter and thread under the subcaudal scales. Then, the thread is used to tie the transmitter to the dorsal surface of the snake.
Snakes will be implanted with TXC-007B radio-transmitters manufactured by Telenax™. Snakes will be kept during 48 hr after implantation to let implantation wounds to heal. Experimental design includes a control group and a translocated group. Snakes of the control group will be released at the site of capture while snakes from the translocated group will be released at a minimum of 1 km away from its capture site, since home range for Bothrops asper has been estimated up to 13.81 hectars (Wasko & Sasa, 2009).
Snakes will be tracked daily for a period of four months. During tracking we will record the locations of each snake using global positioning system, early in the morning. We will record shelter usage, considering ‘Sheltered’ if completely within structural cover (e.g., hollow log or root system of a tree), ‘Semisheltered’ if partially covered (e.g., in dense herbaceous vegetation, adjacent to the base of a tree), and ‘Unsheltered’ if in the open (Wasko & Sasa, 2009). Additionally we will record rainfall over the previous 24-h period, and maximum and minimum temperature. Following the recommendations of Zdenek et al. (2021) to ensure the safety of specimens during tracking without significant altering their behavior, we will perform handlings every month to check for wounds or shed skin accumulation around the transmitter and give aid if required, and we will measure SVL and weight to monitor body condition.
Challenges
We used part of our available funding to run a pilot study to identify the challenges of our project and fill gaps about the natural history of Bothops asper in our study site.
Bothrops asper is a highly cryptic and sedentary species. Observing it during the day is difficult as it tends to shelter in extremely dense vegetation; at night, the species is active and emerges from its daily shelter to hunt in open areas. It might be seen in small grasses, near trails, or in areas covered with shallow leaf litter. Studies in Costa Rica have shown the number of snakes observed per unit of search effort is 0.03 snakes/(person-hours), translating to an estimated one month with 10 hours of sampling each night to locate our expected 10 snakes.
Radiotracking in the dense vegetation of the rainforest requires adittional effort as singal strength of radiotransmitters is dramatically reduced when a snake is covered in its shelter, the maximum distance at which the signal can be heard is about 100 meters.Pre Analysis Plan
Home range
Home range analysis will be performed using the Kernel Density Estimators (KDEs) and Dynamic Brownian Bridge Models (dBBMMs). KDEs allow prediction of the likelihood of finding an animal in a specific area within its home range, and contrary to the often used Minimum Convex Polygons, it is not sensitive to the number of telemetry points (Reinert, 1992; White & Garrott, 1990). The dBBMMs help to improve accuracy in the analysis of home ranges for GPS telemetry by creating a one-dimensional fix-frequency independent behavioral measure (Kranstauber, Kays, LaPoint, Wikelski, & Safi, 2012). Additionally, dBBMMs do not require a priori knowledge of animal movements, contrary to KDEs (Silva, Crane, Marshall, & Strine, 2020; Silva, Crane, Suwanwaree, Strine, & Goode, 2018). Studies comparing dBBMMs to traditional Minimum cluster polygons and KDE methods for herpetofauna movement patterns found dBBMMs had lower error rates, even where data sets were lower resolution (Silva et al., 2020, 2018).
ANCOVA will be used with snout-vent length (SVL) as the covariate to determine whether home range size differed between translocated and control groups and by each estimation method while controlling for effects of body size.
Movement analysis
Straight line distances will be calculated with ArcGIS (ESRI, 2018) for each movement to calculate Average Daily Movement (ADM), Mean Distance per Movement (MDM), Linear Distance from Release Site (LDRS) and Movement Frequency using the Point Distance function. The average daily movement will be calculated by averaging the distances for each day tracked, including days of immobility. Mean distance per movement will be calculated for each individual by dividing the sum of their straight-line distances with the number of days where movement occurred. Linear Distance from Release Site will be calculated as the average distance of track points to the release site and Movement frequency will be calculated as the percentage of days where movement occurred.
Independent sample t-tests will be conducted to assess if there is any significance in the difference between the movement variables of control and translocated snakes over the complete period tracked. To assess the effect of rainfall and temperature on movement patterns, correlation between daily rainfall, temperature and daily movement will be analyzed independently.
Protocols
This project has not yet shared any protocols.