IT IS time to take back the night for wildlife. That was the rallying call from a landmark session on light pollution at the on 4 July in Edmonton, Canada.
The disruptive effects on animals of our penchant for bright lights has rarely impinged on public consciousness. Notable exceptions are when turtle hatchlings head inland to the bright lights of a beach resort instead of the safety of the moonlit sea, or birds collide en masse with brightly lit buildings.
It is rapidly becoming clear, though, that light pollution subtly interferes with the growth, behaviour and survival of many nocturnal species – not just those that hit the headlines.
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The threats posed by the humble street lamp do not rival the wholesale destruction of tropical forests and other habitats, or indeed the threat of climate change. But participants in at the Edmonton meeting agreed that planners should spare a thought for wildlife when installing lighting. “We’ve taken away the night,” warns of the University of Southern California in Los Angeles, who chaired the session.
For instance, Emma Stone of the University of Bristol, UK, has shown that high-pressure sodium street lights can divert from their usual routes between roosts and foraging grounds. Such diversion may be energetically costly – all the more of a worry as the bats in the study were pregnant.
“The glare of street lights diverts some pregnant bats from their usual commute to get food”
Many migratory birds also fly at night, and can be disoriented by brightly lit structures, circling them until they become exhausted, or . Surveys over 25 years at a single TV broadcasting tower in Florida recorded more than 42,000 casualties involving 189 species.
of Fordham University in New York City is now using microphones and radar to track birds through urban environments. He has found that more birds fly over darker and quieter sites like the Bronx Zoo and Central Park, and that those trying to navigate busy districts like Little Italy and East Harlem tend to call out much more, suggesting that they are disorientated.
Nor does it take New York City’s bright lights to disrupt animals: recent studies on frogs have shown that lights barely brighter than a full moon can have profound effects. , New York, found that exposing the tadpoles of the South African clawed frog () to 1 lux every night for 37 nights slowed their transformation into froglets. That’s little brighter than a full moon, and typical of a light-polluted marsh in Utica. If native frogs are similarly affected, it could threaten their survival: delayed development can be fatal for frogs breeding in ponds that are susceptible to drying up.
Yet in some circumstances it may be possible to design wildlife-friendly lighting. Hanneke Poot of the in Seewiesen, Germany, has come up with a way of reducing the number of birds killed at offshore oil and gas rigs. Working on the Dutch island of Ameland in the North Sea, she shone lights of different colours at migrating birds flying south from Scandinavia.
White lights, generally used on rigs, caused more than 80 per cent of birds to change direction on overcast nights. Red lights were only a little less disorienting, but with green lights just 27 per cent shifted course when the skies were overcast, and only 5 per cent were swayed by blue light. Although humans don’t see well in blue light, in tests on a Dutch gas rig, workers were happy with green light, finding that it gave good contrast. Preliminary results indicate that only half the normal number of migratory birds circled the green-lit rig.
Most commonly used lights have different effects on wildlife depending on their precise spectra (see diagram). of the University of Mainz, Germany, has found that different street lights attract and kill vastly varying numbers of insects. The least disruptive, he found, were those using LEDs, especially the “warm” variety that emit less blue light.
Still, Longcore warns that what’s good for one species may be bad for another. “I don’t think we’re going to find a perfect light that will have a low effect on all wildlife,” he admits. Ultimately, there is only one simple way to reclaim the night for wildlife: dim the lights.
