Movement Behavior and Habitat Selection of Rat Snakes (Elaphe spp.) in the Fukushima Exclusion Zone
The 2011 nuclear accident in Fukushima, Japan was one of the largest anthropogenic releases of radioactive contamination in history, and many questions remain regarding its ecological impacts. As part of a larger study estimating animal movements and radiation exposure within the impacted area, we used a combination of VHF and GPS transmitters to estimate home range size and habitat use of nine Japanese rat snakes (Elaphe climacophora and E. quadrivirgata) over three months within the Fukushima Exclusion Zone. Short-term a-LoCoH ranges varied from 0.15–6.80 ha, and daily movements ranged from 30–116 m. Short-term home ranges included more areas close to streams, buildings, and roads, as well as more grassland and less evergreen forest than expected given the availability of these habitat components on the landscape. Within their home ranges, snakes selected areas close to streams and avoided evergreen broadleaf forests. They also frequently used habitat features such as trees and buildings, although use of buildings was highly variable among individuals. The limited distance snakes moved compared to more mobile species suggests snakes could be useful bioindicators of local contamination. However, radionuclide exposure will still vary considerably among individual snakes within localized areas due to differences in habitat use.
Elaphe climacophora with VHF transmitter (left) and GPS transmitter (right).
(A) Map of the evacuated Fukushima Exclusion Zone (FEZ) in red in relation to the Fukushima Daiichi Nuclear Power Plant (FDNPP; yellow triangle), with the entirety of Japan in the inset map for reference. Habitat selection for Japanese rat snakes (Elaphe spp.) at the population scale was calculated by comparing habitat characteristics at random points generated in the available habitat (purple) to characteristics at snake relocations (bounded in blue by a 100% Minimum Convex Polygon). (B) Snake GPS and VHF relocations (n = 1,717) collected June–August 2018 and color-coded by individual.
Average selection ratios and confidence intervals for land cover types at the (A) population scale and (B) home range scale, derived from 1,717 relocations from nine rat snakes (Elaphe spp.) tracked June–August 2018 within the Fukushima Exclusion Zone in Fukushima, Japan. Land cover types include Rural—rural developed areas including buildings and open areas; Grass—grassland, including abandoned rice paddies; DHW—deciduous hardwood; DSW—deciduous softwood; EC—evergreen conifer; and EBL—evergreen broadleaf. Note differing y-axis scales.
Average selection ratios for (A) distance to building, (B) distance to edge, (C) distance to stream, and (D) distance to road. Selection ratios were derived from 1,717 relocations from nine rat snakes (Elaphe spp.) tracked in June–August 2018 within the Fukushima Exclusion Zone in Fukushima, Japan. Gray points represent selection ratios at the population scale; black points represent the home range scale. Note differing y-axis scales.
Contributor Notes
Associate Editor: J. W. Snodgrass.