Light Pollution Shuts Down the Anti-Bat Defenses of Moths

Cape serotine bat (Eptesicus capensis), South Africa / Bernard DUPONT via Flickr CC BY-NC-SA 2.0
Janet Fang 10 Feb 2015, 20:11

Bats and moths have been one-upping each other for millions of years. When moths develop a new anti-bat defensive maneuver, the stealthy bats will come at them with, say, echolocation calls outside the range of moth hearing. But the latest move in this millennia-old co-evolutionary arms race comes from us: Every time a street lamp flips on, we throw off a moth’s defensive behavior. According to a Journal of Applied Ecology study, light pollution may be shifting the balance in this ancient predator-prey relationship.

Cape serotine bats (Neoromicia capensis) are nocturnal insect eaters living throughout Sub-Saharan Africa, and because they don’t specialize on moths, they have echolocation calls that moths can hear. To determine the effect of our lights on a free-living community of bats and eared moths, a team led by Corneile Minnaar from the University of Pretoria compared prey selection by Cape serotine bats in naturally dark settings with that of artificially lit conditions. 

Moth consumption by these bats, they found, was low under unlit conditions. Turns out, they don’t really eat moths all that much in naturally dark settings. But with lit conditions, moth consumption increased six-fold. That increase occurs despite a decrease in relative moth abundance. The team then developed different models based on a variety of prey-selection factors to help explain this difference in bat diet that they observed. According to the model that fit their experimental results the best, the increase in eared-moth consumption was a result of decreased defensive behavior caused by light. The moths were far more evasive in the dark. 

The findings suggest that eared moths—as well as moth-eating specialists (like the bat species who do use calls that aren’t heard by moths)—could be facing a greater risk of extinction due to light pollution, compared with generalist bat species like Cape serotine bats. Moth-hunting specialists avoid light, Nature explains, and tend to fly slower than other bats, making them more vulnerable to predators like owls and bat hawks. And that “is quite a worrying sign,” Minnaar tells Nature. Lights should be developed to be less attractive to moths, the authors say, but the market preference for broad-spectrum lighting make moth-friendly lighting unlikely. However, reducing the redundancy in outdoor lighting and restricting light inside nature reserves and urban greenbelts could help maintain dark refuges for bats and moths. And these may become important for their persistence.

Image: Bernard DUPONT via Flickr CC BY-NC-SA 2.0

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