Bright Side of the Night – 2.3.1

Reactions of Wildlife on Disturbances Like Light Pollution

The Consequences of Artificial Light

Animals and plants cannot darken their habitat with blinds. They are at the mercy of artificial light. Many moths and others insect species, for instance, are strongly attracted to artificial light at night. Most probably, the reason is that they usually navigate with the help of light from the sky. Artificial light therefore interferes with this mechanism, and impairs orientation. The strongest attracting effect comes from emissions in the ultraviolet, short-wave, visible range. Nocturnal insects are thus lured away from their natural habitats. Once the animals reach the beam of light, they either become inactive or they continue to buzz around the source of light until they either die of exhaustion or lose a significant amount of energy. They are also at risk of becoming easy prey.

Light Pollution Affects Migrating Birds

Artificial light influences bird migration, too. About two thirds of migratory birds fly at night to take advantage of darkness for protection from predators and also to save time, energy and water. Point light sources and large illuminated areas, for instance, can lead to disorientation and considerable energy losses. In the worst case, birds collide with structures and are killed. The higher the structure and the more exposed the site, the more likely it is that the illuminated facility will become a trap for migratory birds. The Alpine Arc is an important crossing point for migratory birds. Mountain passes and illuminated ruins, mountain refuges and ski slopes or other lighting installations can therefore be critical for migratory birds.

Bats’ Habitats Are Fragmented

Illuminated objects, searchlights or large-scale sites such as sports facilities can also disturbe migrating bats. They may become confused or lose their orientation as a result. Since the 1980s, about a third of all bat roosts have disappeared from churches in Sweden, for instance. This correlated precisely with the installation of building illumination. Researchers also observe that lesser horseshoe bats, for instance, avoid artificially lit flight paths which they had used before. Scientists fear that these detours cause the bats to spend excessive amounts of energy as a result. On a larger and permanent scale, therefore, habitats are fragmented and reduced.

Artificial Light Irritates Most Fishes

Fisheries, in turn, use artificial light to attract fish, squid, and other edible marine animals at night. Predatory fish also have discovered the phenomenon to their advantage. The attraction effect of artificial light is also used to guide the fish onto fish ladders on dams. Many fish species are deterred by artificial light. The rainbow trout, for example, feeds mainly on dark nights, and not in artificially illuminated areas or during a full moon. It is also for good reasons that the European eel avoids water areas illuminated by artificial light during its nocturnal migration. Indeed, illuminated bridges can be the eel’s undoing.

Turtles Losing Their Bearings

Artificial light sources located near beaches can cause problems for many animals and plants. Freshly hatched turtles for instance lose their sense of orientation – often with fatal results. They hatch out at night when the temperatures are lower. When they emerge from the sand, they have to find their way straight to the sea. For that purpose they make use of local light stimuli; the hatchlings move in the direction of the lighter surface of the sea lower down the beach, in which the light of the celestial bodies is reflected. All this is disturbed when artificial light illuminates the buildings, streets and sites at the beach. The hatchlings get so disoriented that they move inland, where they are run over by vehicles or die of exhaustion.

The list could be continued ad infinitum—it is widely shown today that the majority of animals and plants and their development and life cycles are disturbed by artificial light exposure.

Which wavelength range and illuminance values are harmful?

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*Herons migrating south for winter. Image by Gerhard – Pixabay*

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Videos

UD explores how light pollution affects migrating birds University of Delaware)