The orange and black dorsal pattern of cave salamanders (Eurycea lucifuga) is highly visible in daylight, but they are active at night and in low-light environments. We assessed whether this pattern was effective at deterring predators in both daytime and nighttime light. We set up a 7x9 grid of 1 m2 plots around Sauerkraut Cave in Louisville, Kentucky, which has a high population of E. lucifuga. Plots were placed at a distance of 5 m from one another; we established a total of 60 plots, omitting 3 sites immediately outside the cave. Each plot had 2 plasteline salamander models, one painted orange with black spots to resemble E. lucifuga and one painted a dark brownish grey that is difficult for humans to see on the forest floor. We surveyed the plots at dawn and dusk to collect and replace models that were attacked, and we recorded the time of attack as day or night. We identified would-be predators by markings they made on the models. We also assessed where on the models predators preferred to attack by comparing the number of bites on models’ heads, bodies and tails to the relative area of each of these sections.
A total of 62 models were damaged by predators, with more damaged during nighttime hours than during the day (54 versus 8; c2 test, p< 0.001). Orange models were significantly less likely to be attacked by would-be predators than were grey models (20 orange versus 42 grey models; c2 test, p = 0.005). Most attacks during the daylight hours were by birds, which preferentially attacked grey models (c2 test, p = 0.020; 15 total attacks). A total of 42 attacks were by mesomammals, specifically raccoons and opossums, which, considered together, also avoided orange models in favor of grey models (p = 0.013). While birds have excellent color vision, raccoons and opossums do not. Considering that raccoons have monochromatic vision and opossums likely have difficulty distinguishing colors, the defensive benefit of E. lucifuga’s dorsal pattern in low-light conditions probably comes from luminance contrast rather than chromatic contrast. We could determine where the predators damaged 37 of the models, which had 49 total bites. Predators preferentially attacked the heads of grey models (p < 0.006). This suggests that predators do perceive these models to be prey and attempt to subjugate them quickly.