What happens at night just beyond our doorstep? Nighttime is not necessarily bedtime, at least not for many animals. After all, many animals don’t wake up until the sun goes down. About two-thirds of the world's animal species are nocturnal, including about half of all insect species.1

Nocturnal animals depend on darkness and natural light from the moon and stars for orientation, movement, breeding, hunting or foraging, and avoiding predators and food competitors. Artificial light at night affects physiological functions and processes as well as animal behaviour: they may be unnaturally attracted to or repulsed by artificial light or lose their orientation.

1 Hölker F, Moss T, Griefahn B et al. (2010) The Dark Side of Light: A Transdisciplinary Research Agenda for Light. Ecol Soc 15(4):13.

Translation: Project SKYSCAPE ITAT 2047, KP Interreg Italien-Österreich 2014-2022

Predators and their prey

© Amber Catford

The eagle owl is the largest owl in the world. It can turn its head up to 270 degrees. The owl’s most important sensory organ is the ears, which helps it to locate and strike prey in total darkness. Nocturnal mammals avoid open areas under the light of the full moon (max. 0.3 lx). Limiting their activity at such times probably helps them to avoid being seen by potential predators.1 In turn, eagle owls have been increasingly observed when the moon is full, covering longer distances and flying faster.2 Such studies suggest that animals change their behaviour in accordance with the amount of available light. Light pollution from illuminated valleys and cities penetrates into natural areas and affects the habitat and the species that live there.

1 Beier P (2006) Effects of Artificial Night Lighting on Terrestrial Mammals. In: Rich C, Longcore T (Hg): Ecological Consequences of Artificial Night Lighting. Island Press.
2 Penteriani V, Kuparinen A, Delgado MD et al. (2011) Individual status, foraging effort and need for conspicuousness shape behavioural responses of a predator to moon phases. Animal Behaviour 82, 413-420.

Bird migration

© Amber Catford

Most migratory birds migrate at night because they are exposed to less air turbulence and are better able to conserve energy. The main migration periods are from February to May and from August to November. Migratory birds (as well as migrating bats) are disturbed and may become confused or lose their orientation as a result of illuminated objects, searchlights and large-scale illuminated areas - sometimes with fatal results.1, 2 At the edges of the Alps, at mountain crossings and in some valleys, bird migration becomes heavily concentrated, which is why the illumination of castles, mountain huts, summit crosses etc. should be avoided at these locations. For animals in these areas, wind turbines can also be lethal. Around new moon, illuminated buildings become even more attractive. Studies show that continuous lighting attracts and irritates more migratory birds than flashing light.3 This insight is significant when it comes to warning lights for air traffic.

1 Haupt H, Schillemeit U (2011) Lichtanlagen bringen Zugvögel vom Kurs ab. Natur und Landschaft. 43(6):165-170.
2 Voigt CC, Roeleke M, Marggraf L et al. (2017) Migratory bats respond to artificial green light with positive phototaxis. PLoS ONE 12(5):e0177748.
3 Gauthreaux SA, Belser CG (2006) Effects of Artificial Night Lighting on Migrating Birds. In: Rich C, Longcore T (Hg): Ecological Consequences of Artificial Night Lighting. Island Press.

Our secretive neighbours

© Amber Catford

More and more, people feel disturbed by their neighbour’s excessive use of light. Luckily for people, they can at least discuss this problem and come to a solution. But if your neighbour is the secretive, endangered garden dormouse, you should be aware that this nocturnal rodent needs darkness to avoid predators and forage with it’s highly acute, well-adapted senses. The dormouse is an omnivore. It will even eat slugs if given the chance. In spite of their name, however, garden dormice prefer to live in the woods. Nocturnal artificial light reduces and fragments the habitat of mammals and increases the risk that they become easy prey. In fact, studies show that the brightness of the full moon (max. 0.3 lx) is already enough to reduce activity and food intake amongst many rodents.1 Similarly, plants also regenerate at night and continuous exposure to light damages their ability to photosynthesise.2

1 Beier P (2006) Effects of Artificial Night Lighting on Terrestrial Mammals. In: Rich C, Longcore T (Hg) Ecological Consequences of Artificial Night Lighting. Island Press.
2 Kwak MJ, Je SM, Cheng HC et al. (2018) Night Light‐Adaptation Strategies for Photosynthetic Apparatus in Yellow‐Poplar (Liriodendron tulipifera) Exposed to Artificial Night Lighting. Forests 9(2):74.