A light in the dark: Moon phase affects capture rate of the endangered American burying beetle
The moon affects marine habitats by regulating tides, and nocturnal light levels change as a function of moon phase, having a profound influence on animal behavior both in oceans and on land. By enhancing or dampening the use of visual cues, inducing breeding synchrony, or affecting the activity of competitors, predators, or prey, the moon’s illumination has lit the evolving world for millennia. Increases in artificial lighting due to urbanization and industrialization can disrupt natural habitats and alter behaviors influenced by moonlight, producing changes in the growth rates and distributions of animal populations. The American burying beetle (Nicrophorus americanus), once widely distributed east of the Rocky Mountains, is now federally endangered. The factors driving this population decline remain largely unknown. Curiously, a closely related and ecologically similar burying beetle, Nicrophorus orbicollis, remains abundant throughout most of its historical range. This presents an interesting puzzle: what ecological factors are affecting N. americanus but not N. orbicollis? We use two sets of trapping data, from Nebraska and Oklahoma, to examine the effects of nighttime illumination and weather on capture rates to test the hypothesis that N. americanus is more sensitive than its congener to changes in ambient light.
Nicrophorus americanus was affected by moonlight levels at both sites; as nights got brighter, foraging activity declined. This effect was largely negated by the presence of cloud cover. In Oklahoma but not Nebraska, fewer beetles were caught on cloudy nights overall, perhaps due to amplification of sky glow from a nearby city. In Nebraska, where it was windier and cooler, N. americanus capture rates were also negatively affected by high wind and low temperature. Capture of N. orbicollis was also altered by the moon, but either positively or not to the degree of N. americanus. Indifference to or preference for elevated light levels could have contributed to the relative success of N. orbicollis in well-lit areas where N. americanus has disappeared. Conservation efforts should focus on preserving not only the palpable habitat of vulnerable species but also on altered aspects of their sensory environment. Changes in animal activity can cause broad ecosystem effects, and it is critical that as the human population grows we understand our impact on the living world. We lack information about the moon’s effects on many other nocturnal animals’ behavior, especially in terrestrial systems where light pollution is most likely to disrupt natural rhythms.