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November 2010, Volume 8, Number 11
Hiding from the Lights

City dwellers often see bats flying around streetlights, happily chasing insects that are attracted to the glow. But such lights, especially in rural areas, can also have a dark side for bats. Research by graduate student Emma Stone in the United Kingdom found that artificial lighting can interrupt some bats’ nightly journey from roost to foraging habitats.

Stone’s project, which used a novel experimental approach, was supported in part by Bat Conservation International Student Research Scholarships.

Light pollution is fast becoming a global phenomenon, but the impact on wildlife, including bats, is rarely studied. The bats reported foraging at streetlights are usually fast-flying species accustomed to open landscapes. Such bats are better than their slower cousins at evading hawks, owls and other birds of prey.

The lesser horseshoe bat that Stone studied is, by contrast, a shy, slow-flying bat that’s adapted to cluttered woodlands. It typically travels no more than about 1.2 miles (2 kilometers) from its roost to forage each night. These bats frequently fly along hedgerows – densely wooded of shrubs and small trees – for protection from predators and the elements.

Stone conducted her artificial-lighting experiments along hedgerows in eight sites around southern Britain. She first surveyed light levels at currently illuminated hedgerows, then duplicated those levels at experimental sites. Her team installed two temporary, generator-powered lights that mimic the intensity and light spectra of streetlights. Each site was near a maternity colony and along confirmed commuting routes of lesser horseshoe bats.

Bat activity at each site was monitored with bat detectors, which allowed identification of horseshow bats during four specific treatments: control (with no lights); noise (generator on and lights installed but switched off); lit (full illumination all night for four consecutive nights); and another night of noise only.

No significant difference in activity levels was detected between the control nights and noise nights. The impacts came when the lights were switched on. “We documented dramatic reductions in activity of lesser horseshoe bats during all illuminated nights,” she reports. Thirty percent of horseshoe bats reversed direction and left before reaching the lights; 17 percent flew over the hedgerows; 9 percent flew through the thick hedgerow vegetation; and 2 percent circled high or wide to avoid the lights.

These results, Stone said, suggest that light pollution may fragment the network of commuting routes used by lesser horseshoe bats, causing them to seek alternate, and probably longer, paths between roosting and foraging habitats. For some bats, this increased flight time can increase energy costs and stress, with potential impacts on reproductive success. It is critical, therefore, that light pollution be considered in conservation efforts.

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BCI Members can read the complete story of Emma Stone’s light-pollution research in the Winter 2010 issue of BATS magazine.

You can help support vital bat research and conservation around the world through BCI’s Student Research Scholarships and other critical projects by visiting www.batcon.org/donate

All articles in this issue:
BCI Workshops
Capture and identify a stunning array of bats and learn the latest bat research and management techniques during Bat Conservation ...

Hiding from the Lights
City dwellers often see bats flying around streetlights, happily chasing insects that are attracted to the glow. But such lights, ...

Bats in the News
Bats are often remarkably agile flyers. Species that live in cluttered, forest habitats routinely dodge branches and foliage ...

Unless otherwise noted, all images are copyright ©Merlin D. Tuttle and/or ©Bat Conservation International