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?

Herons migrating south for winter. Image by GerhardPixabay

Further Resources

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

Light Pollution and Its Impact on the Ocean (What We Can Do)

Why you should care about light pollution (DW Planet A)

Auswirkungen von Lichtverschmutzung auf Lebewesen (Natur braucht Nacht)

Lichtverschmutzung Kurzbericht (XEN.ON TV)

Uccelli migratori: traffico intenso a Nord-Est – Veneto Agricoltura

Critiche al Water Light Festival: uccelli migratori disorientati – RAI

Il fascino della migrazione

Zoologi e Speleologi: insieme per conoscere e proteggere i pipistrelli – RAI

Animali: le tartarughe marine – NatGeoTV

Online Resources

The influence of light pollution on plants, animals and ecosystems (Helle Not)

What happens at night just beyond our doorstep? Bothersome-Brightness-Cartoons. (Helle Not)

Verlust der Nacht / Loss of the Night: Interdisciplinary Research network

Into the Night in the Kaunertal Valley (Online publication)

Website engaging in research and conservation of fireflies (DE/FR/IT)

Buglife: A Review of the Impact of Artificial Light on Invertebrates

Global light pollution is affecting ecosystems—what can we do? (UN Environment Programme)

Unterwegs in die Nacht im Kaunertal (Online publication)

Konzept zur nachtbezogenen Naturpädagogik (Online publication)

La luce artificiale sta cambiando il comportamento degli insetti notturni – Focus

Vuoi aiutare la fauna selvatica? Spegni la luce! – National Geographic

L’inquinamento luminoso minaccia gli uccelli migratori: disorientati, si schiantano contro gli edifici o diventano prede – La Stampa

L’inquinamento luminoso è un serio pericolo per gli organismi marini che si orientano con la luce – Kodami

Tartaruga marina – animali in via di estinzione – WWF

L’inquinamento luminoso minaccia la vita marina – National Geographic

Further Readings

Regularly updated Literature and links with regards to light pollution and dark skies (Helle Not)

Literature & Links on the website “Verlust der Nacht/Loss of the Night”

Scientific Paper: Street Lighting Disturbs Commuting Bats (2009)


Analyse der Auswirkungen künstlichen Lichts auf die Biodiversität (NaBiV Heft 168, 2019)

Pipistrelli e inquinamento luminoso – Centro Regionale Chirotteri

Influenza di fattori ambientali e attività umane sul successo della nidificazione di Caretta caretta (Linnaeus, 1758) lungo le coste italiane – Tesi di laurea di Luca Ceolotto

Teaching Material

Teaching Material Kit on Light Pollution and its negative effects in 4 Languages (English, Spanish, German, Portuguese) (Stars4all)

For Kids

Materials for young scientists: Quiz, Arts and craft corner, App and Exhibition for schools. (Loss of the Night network)

Unterrichtsmaterialien für Schulen – “Lichtverschmutzung” (Die Umweltberatung)

Wissens- und Methodenbox „Kunstlicht, Nacht und Sternenhimmel“ (Naturfreunde)

La migrazione degli uccelli – YouTube