Published online July 18, 2022
Journal of Ecology and Environment (2022) 46:18
© The Ecological Society of Korea.
Division of Science Education, Kangwon National University, Chuncheon 24341, Korea
Correspondence to:Daesik Park
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Background: Radio-telemetry is a useful method to investigate the spatial ecology of species in the wild, by tracking the signal of a transmitter attached to an individual. The method of attaching a transmitter to a snake is representatively divided into surgical implantation, and external attachment, which latter is often used in small snake species.
Results: In this study, we evaluated and compared the utility of two external attachment methods, the nylon thread method and the tape method, applied to a small grassland snake species of approximately 50 cm snout–vent length, the Slender racer (Orientocoluber spinalis), on an island in the Republic of Korea. The nylon thread method and the tape method were applied to four and five individuals, and radio-tracked for an average of eight and eleven days, respectively. The nylon thread method caused individual injury and disturbed their movement, while using the tape method, the transmitter package sometimes dropped off, but no injury or movement problems occurred.
Conclusions: Considering that poor understanding of how to attach the transmitter makes it difficult to investigate the spatial ecology of small snake species, the tape method, evaluated in this study, could be applied to attach a transmitter and to study spatial ecology of such snakes.
Keywords: nylon thread method, Orientocoluber spinalis, radio-telemetry, tape method
The secret lifestyle of wild animals is effective at foraging prey and protecting them from predators, but it also makes them difficult to observe in the field. These characteristics limit the investigation of the lifecycles and ecology of wild animals, specifically snakes (Gerald et al. 2006). Radio-telemetry is a highly effective method to investigate the spatial ecology of animals in the wild (Balmori 2016; Bergman 2005). Radio-telemetry generally requires direct capture of individuals and attaching the transmitter to the individuals. Also, before attaching the transmitter to the individual, various considerations must be made, such as the attachment method of the transmitter, the body size of the snakes, and the tracking period to achieve the study goal.
The transmitter attachment method to snakes is largely divided into surgical implantation and external attachment. Surgical implantation, which has been applied to various snake species (Gerald 2006; Kim et al. 2012a; Lee et al. 2011; Lee and Park 2011; Mohammadi et al. 2014; Webb and Shine 1998), is a method of inserting the transmitter into the subcutaneous layer or the abdominal cavity of an individual, and if necessary, fixing the transmitter to the ribs (Reinert and David 1982; Weatherhead and Anderka 1984). Implantation of the transmitter into the abdominal cavity causes the fewest side effects caused by the transmitter for radio-tracking snakes, and its strong fixation makes stable long-term study possible. However, veterinary surgery is required for operation, anesthesia, abdominal cavity incision, and suture. This method also needs about a two-week recovery period after the surgery, often resulting in the death of the individual from various infections (Lee and Park 2011; Lentini et al. 2011; Shine and Lambeck 1985; Smith et al. 1988). Subcutaneous implantation is relatively simple since only the skin incision and suture are necessary to insert the transmitter under the skin (Újvári and Korsós 2000). However, the protrusion of the transmitter insertion site may interfere with the snake movement by contact with external objects, and break the suture (Újvári and Korsós 2000; Weatherhead and Anderka 1984). Therefore, the surgical implantation method is often not applicable to small-sized snake species (Anderson and Talcott 2006; Madrid-Sotelo and García-Aguayo 2008; Wylie et al. 2011).
If the body size of the species is too small to apply surgical implantation, or surgery is not affordable, the external attachment method can be adopted. This method is a much more non-invasive method than surgical implantation and is a convenient technique to replace or remove the transmitter from the individual (Wylie et al. 2011). Typical external attachment methods to snakes include the nylon thread method (Ciofi and Chelazzi 1991), tape method (Wylie et al. 2011), and glue attachment method (Riley et al. 2017), although the transmitter can often be attached with a harness for lizards, which have legs (Kim et al. 2012b; Park et al. 2019). The nylon thread method fixes the transmitter by inserting a nylon thread that is connected to the transmitter into the tail of a snake (Ciofi and Chelazzi 1991). The nylon thread method has been applied to various snake species (Wolfe et al. 2018; Scali et al. 2008), but the suitability for slender-bodied small snakes has not been verified. The tape method uses tape to fix a transmitter to the body parts of an individual and is easy to apply without surgery (Madrid-Sotelo and García-Aguayo 2008; Tozetti and Martins 2007; Wylie et al. 2011). But in the tape method, transmitters often detach, particularly during the long-term study (Tozetti and Martins 2007; Wylie et al. 2011). The glue attachment method attaches the transmitter to the dorsum of a snake using super glue, and can be applied restrictively to species that have low activity and do not use crevices as shelters (Cobb et al. 2005; Riley et al. 2017). If a suitable method of external transmitter attachment is selected based on a species’ ecological characteristics, it could provide diverse ecological information, such as habitat preference, daily movement patterns, and temporary range expansion (Harris et al. 1990).
In this study, we evaluate two transmitter attachment methods of the nylon thread method and the tape method to externally attach a transmitter to small grassland snakes of the species, Slender racer (
To attach transmitters, we used the nylon thread method and the tape method. To apply the nylon thread method, we connected two 0.33 mm nylon fishing threads (X-hard 4.0; Essen, Tokyo, Japan) to the holes in the front and rear parts of the transmitter, passed the threads through near the 23rd ventral scales on the tail from the cloaca using the suture needle, and tied threads to the transmitter (Ciofi and Chelazzi 1991). Because the needle and thread can cause potential damage to internal visceral organs and blood vessels when fixing the transmitter to the body, we attached the transmitter to the tail to exclude such risks. After attaching the transmitter, we applied small amounts of epoxy on the front of the transmitter, making the part streamlined in shape so that herbs and branches would not disturb the individual movement, as far as was possible (Fig. 1). Because the antenna of the transmitter was very flexible, we did not fix it on the body, so as not to interfere with the snake’s movement. Since a thin and sharp nylon thread may scratch the skin, Ciofi and Chelazzi (1991) encased the nylon thread, first, in a rubber tube of which an external diameter is around 1 mm when applying to a large snake,
In the tape method, a transmitter-attached tape is wrapped around the body part of the snake (Wylie et al. 2011). First, we attached the transmitter to 3 cm wide beige duct tape (Task and More Inc., Gyeryong, Korea), which could completely wrap the 1.7 cm long transmitter. Next, the transmitter was fixed once again by covering it with double-sided tape (Woolim-tape, Seongnam, Korea), which tightly attached the transmitter to the duct tape, and also affixed the tape tightly to the snake body. We placed the transmitter at the ventral side of 2/3 SVL from the head, and fixed it by wrapping the body in 1.5 turns of duct tape. We wrapped the tape a little tight, so that the transmitter was slightly pushed into the abdominal cavity side, and did not protrude too much from the snake’s body. This ventral placement procedure of the transmitter could help to prevent snakes from snagging off the package when passing through various obstacles (Wylie et al. 2011). Lastly, we applied super glue (Super glue 412; Amos, Seoul, Korea) to the outermost edge part of the tape to prevent accidental tape detachment (Fig. 1). In this method, we also did not fix the antenna of the transmitter.
After confirming that the transmitter did not disturb
We conducted Mann–Whitney U-test to verify the difference in individual size, transmitter package weight, the proportion of transmitter package to body weight between the two attachment methods, and the mean daily moved distance. All numerical data are presented as mean ± 1 standard error unless otherwise noted.
During the study, we radio-tracked total nine
We tracked the snakes applying the nylon thread method for 8.3 ± 5.4 standard deviation (SD) days (range: 3−15) over 9.3 ± 5.7 SD relocations (range: 4−16). They daily moved 31.3 ± 14.8 m (range: 4.6−73.0). The signal of OS01 was stuck for more than seven days under the rock from three days after its release. So, we considered OS01 dead and ended the tracking trial. We observed OS02 to be severely injured on the tail where the transmitter was attached, so ended its tracking (Fig. 2). OS03 was successfully tracked for more than 15 days, and the case was considered complete. We found OS04, which was stuck in a rock crevice due to the transmitter package, on the fourth day of its release. We rescued it and ended its tracking (Fig. 2). After removing transmitters and applying anti-virus ointment (Madecassol Powder, Dongkook Pharmaceutical, Seoul, Korea) to the wound area, we released OS02 and OS04 into the wild.
Individuals applying the tape method were tracked for 11.0 ± 4.0 SD days (range: 7−15) over 19.4 ± 7.8 SD relocations (range: 9−28). The snake daily moved 20.2 ± 6.5 m (range: 4.1−39.6). We lost the signal of OS05 six days after release and considered it as signal loss. The signals of OS06 and OS07 did not move under the rock from five and three days after their release, respectively, so we considered them as cases of transmitter detachment. Later, we found OS07, of which the transmitter package was detached 6 days after ending our tracking trial. OS08 and OS09 were successfully radio-tracked for more than 15 days and were considered complete cases.
In the results, the nylon thread method had the advantages that the transmitter package was light, and was attached tightly. However, this technique is not suitable for snake species that use narrow rock crevices as shelters or corridors, because the transmitter package disturbed the movement of snakes, and makes them get stuck between crevices such as the case of the OS04. Also, the front part of the attached transmitter might be stuck with grasses or obstacles while the snakes move forward. Backward forces pull the package and the nylon thread toward the tip of the tail. As a result, the nylon thread, which is strongly pulling backward, may have been responsible for the injury of OS02. Although the epoxy was applied to the front part of the package in a streamlined shape to reduce the backward force, this was not effective enough to prevent such injury. As in previous studies (Ciofi and Chelazzi 1991), wrapping the nylon thread in a rubber tube might help to prevent from such injuries to some extent, but the tail of
In previous studies, the tape method of transmitter attachment was applied to
Poor understanding of how to attach the transmitter makes it difficult to investigate the spatial ecology of small snake species. For this reason, the study of several Korean snakes, including the endangered Chinese many-tooth snake (
We thank Min-Seok Do and Hoanjin Jang for providing information on the study site and helping field works.
IKP did conceptualization, data curation, formal analysis, investigation, writing-original draft, and writing-review and editing. HJ did data curation, investigation, and writing-review and editing. DP did conceptualization, funding acquisition, supervision, writing-original draft, and writing-review and editing.
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (No. 2020R1I1A3051885).
The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.
This research was conducted within the guidelines and approval of the Institutional Animal Care and Use Committee of Kangwon National University (KW-200707-3).
The authors declare that they have no competing interests