The effects of artificial night lighting on the nocturnal activity of juvenile Ambystoma maculatum

As human development increasingly expands into natural habitats, artificial light at night (ALAN) has become a growing problem that has the potential to negatively impact wildlife. Many organisms are heavily dependent on external lighting cues, such that any alternations to these cues above typical environmental light levels could potentially disrupt circadian rhythms and any subsequent behaviors. I examined the nocturnal behavior of recently metamorphosed juveniles of the spotted salamander, Ambystoma maculatum, that were kept under a 16L: 8D photoperiod and randomly assigned to three lighting treatments at night: 0.0001 lx (dark); 0.1 lx; and 1 lx. Day lighting for all treatments was kept at 100 lx. An infrared camera recorded each individual's activity during scotophase and was later reviewed for time to first emergence from the cover objects and total time spent active outside of the cover object. Activity 1 hr prior to lights off was also observed. Individuals assigned to the 1 lx treatment emerged from under the cover object significantly sooner than those in the dark control (0.0001 lx) treatment. Additionally, although differences were not statistically significant (P = 0.053), juveniles in the 1 lx treatment trended towards spending more time active outside the cover object than individuals in the dark control (0.0001 lx) treatment. There was, however, a significant difference in the proportion of juveniles active one hour prior to dark in the different lighting treatments: those in the 1 lx treatment were more likely to be active 1 hr before dark than individuals in the dark control (0.0001 lx) treatment. These results provide evidence that ALAN can disrupt the nocturnal behavior of juvenile salamanders, such that activity above-ground is disrupted. Additionally, these data provide the most extensive observation of the nocturnal activity of Ambystoma maculatum outside of the breeding season.