Read aloud Hundreds of millions of birds die every year in Europe from collisions with windows and glass fronts. The black birds of prey schemes designed to prevent such collisions are virtually ineffective. With the so-called spiderweb effect, biologists have devised a new method to warn birds about large glass surfaces. They want to take advantage of the fact that birds can see UV light, but not humans. Every child knows them: black birds of prey glued to bus shelters and large glass fronts to keep birds from flying against the windows. Nevertheless, many birds still fly against the glass and injure themselves seriously or fatally. Effective protection against bird strike such as cloth or adhesive tape in front of the window surfaces or hanging with nets are not very aesthetic and are therefore hardly used. But the biology student Martin Regner and the free biologist Friedrich Buer from Neustadt an der Aisch are researching another solution to the problem. They want to use the so-called spiderweb effect to signal the animals effectively: "You better not fly here".

The two scientists of nature have copied this effect: The nets of the spider webs are cleverly protected against the unintentional destruction by birds. The spider silk throws back light from the ultraviolet range of the light spectrum. For humans, these wavelengths are invisible, but birds even see them particularly well and therefore make an arc around the sensitive nets.

For birds, it is very important to be able to see colors in the UV range. The ability helps them with the food and the partner search. For example, many berries and flowers have UV patterns that are hidden from the human eye. Birds of prey benefit in a particularly subtle way from their ability to see UV colors: mouse urine reflects ultraviolet light. If a kestrel shakes over a field, he knows exactly where it's worth the effort, because the mice leave UV traces with their urine. Also for the Dating, the vision in the UV spectrum of light is essential. Males and females of a kind sometimes look absolutely the same to humans. The differences between the sexes are visible only in the UV range.

But glass surfaces reflect UV light too low-contrast for the birds to see. In addition, the animals are easily irritated by reflections. They do not recognize the surfaces as an obstacle and fly unchecked into the windscreen. Cautious estimates give reason to fear that around one hundred million birds will die each year in Europe. The fact that birds see in the UV range, but humans not, could lead to an elegant solution to the bird strike problem, suggest Regner and Buer. UV patterns on the windows, which the human being does not see and therefore do not disturb, could in the future ensure that the animals recognize the obstacles. display

"Now we are getting into the hot phase, " says Regner. The first large field trials are planned for next spring. The scientists want to take advantage of the bird migration. When the migratory birds return from their winter quarters, the number of bird strikes will increase again - a good opportunity to investigate possible uses of the spider web effect under natural conditions. Among other things, in cooperation with the State Bird Watching Authority for Hessen, Rhineland-Palatinate and the Saarland and the Hessian Ministry of the Environment, a glass façade is to be selected in Frankfurt am Main, half of which is treated with a UV-absorbing substance. Since window glass reflects UV light relatively evenly, the substance should provide sufficient contrast, the researchers hope. The other half of the glass front remains untreated for comparison. Suitable substances for the test abound, for example in sun creams.

Later, in collaboration with the University of Frankfurt, laboratory experiments on the spiderweb effect will be carried out. In addition, the researchers in the private sector want to ask whether the industry is interested in the project, says Klaus Richardz of the State Bird Watching Authority in Frankfurt.

For the very impatient Regner and Buer have a tip: "The windows just do not brush, " the biologists advise. Dust and pollen diminish the irritating reflections and swallow some of the ultraviolet light. This is probably enough, so that the birds perceive the discs, have resulted in experiments on Buer's house. Since the biologist no longer cleans his windows, he has hardly any problems with bird strikes - and has been for more than five years.

More about the spiderweb effect and the work of Friedrich Buer and Martin Regner can be found here.

Cornelia Pfaff

© science.de

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