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

Nighttime beneath the surface

© Amber Catford

Some fish are active at night, including the perch, which likes to hunt at dusk. Under laboratory conditions, it was discovered that a light intensity of 1 lx at night could already suppress melatonin production in European perch.1 Hence, humans are not the only ones to experience the phenomenon of inhibited melatonin synthesis caused by artificial light at night. While this hormone is important for our regeneration, for example, its far-reaching effects on many organisms are unknown. The European crayfish is another nocturnal aquatic animal. Crayfish shed their skin mainly during dark phases of the moon. The assumption is that they protect themselves from predators with this adaptation.2 A study in the Canton of Zurich compared the occurrence of native crayfish with existing nocturnal brightness levels. No individuals occurred in potentially suitable habitats with steady brightness levels of over 0.75 lx. Other factors, such as a lack of structure and poor water quality, also threatened the animals at these sites.3 Under cover of the night, small life forms such as water fleas swim towards the water surface and feed on algae there. Even the levels of brightness caused by urban light pollution were enough to suppress its nightly ascent. This can disrupt the aquatic food chain and lead to more frequent algal bloom.4

1 Brüning A, Hölker F, Franke S et al. (2015) Spotlight on fish: light pollution affects circadian rhythms of European perch but does not cause stress. Sci Total Environ 511:516-522.
2 Franke R, Hoerstgen-Schwark G (2013) Lunar-Rhythmic Molting in Laboratory Populations of the Noble Crayfish Astacus astacus (Crustacea, Astacidea): An Experimental Analysis. PLoS ONE 8(7):e68653.
3 Schuler LD, Schatz R, Berweger CD (2018) From global radiance to an increased local political awareness of light pollution. Environmental science & policy 89:142-152.
4 Moore M, Pierce SM, Walsh HM et al. (2000) Urban light pollution alters the diel vertical migration of Daphnia. Verh Internat Verein Limnol 27(1-4):779-782.

The nighttime is for bats

© Amber Catford

Bats use echolocation to orientate themselves in the dark and to catch insects. Echolocation relies on emitting ultrasound and reading the echo. Bats also have light-sensitive eyes. Habitat fragmentation and reduction (e.g. the lesser horseshoe bat1), delayed departure times from roosting sites (e.g. Geoffroy's bat2) and the total abandonment of roosting sites (e.g. brown long-eared bat3) are just a few negative effects resulting from the use of artificial light at night. The common noctule, for instance, hunts insects attracted by artificial light. Meanwhile, the mouse-eared bat avoids illuminated areas altogether.4 The lesser horseshoe bat has disappeared completely in some mountain valleys in Switzerland after street lighting was installed. At the same time, the less light-shy common pipistrelle has spread into these areas instead. The suspicion is that the lesser horseshoe bat disappeared due to competitive pressure. Both species are about the same size and eat the same spectrum of food.5 It has also been observed that some diurnal birds use artificial light at night to their advantage.6

1 Stone EL, Jones G, Harris S (2012) Conserving energy at a cost to biodiversity? Impacts of LED lighting on bats. Global Change Biology 18, 2458-2465.
2 Boldogh S, Dobrosi D, Samu P (2007) The effects of the illumination of buildings on house-dwelling bats and its conservation consequences. Acta Chiropterologica 9, 527-534.
3 Rydell J, Eklöf J, Sánchez-Navarro S (2017) Age of enlightenment: long-term effects of outdoor aesthetic lights on bats in churches. Open Science 4, 161077.
4 Rydell J (2006) Bats and Their Insect Prey at Streetlights. In: Rich C, Longcore T (Hg): Ecological Consequences of Artificial Night Lighting. Island Press.
5 Arlettaz R, Godat S, Meyer H (2000) Competition for food by expanding pipistrelle bat populations (Pipistrellus pipistrellus) might contribute to the decline of lesser horseshoe bats (Rhinolophus hipposideros). Biological Conservation 93:55-60. 6 Baumgart W (2006) Greifvögel und Eulen als Fledermaus-Jäger. Ornithol Mitt 58:292-309.
6 Baumgart W (2006) Greifvögel und Eulen als Fledermaus-Jäger. Ornithol Mitt 58:292-309.

Unrequited love

© Amber Catford

The eggs, larvae, pupae, females (though they are not capable of flight) and males of the small firefly all glow. This special gift is called bioluminescence and it is used to ward off enemies and find mates. Glowing is a result of the luminescent substance luciferin, which is oxidised by the enzyme luciferase. Because artificial light restricts the range and efficacy of the light signals, the fireflies can be restricted from reproducing.1, 2

1 Ineichen S, Riesen M (2014) Kleine Lichter im lichten Wald : Leuchtkäfer leuchten nicht nur – sie stehen auch für eine gut strukturierte Landschaft mit hoher Biodiversität. Zürcher Wald. 2014(4):30-31.

Industrious pollinators

© Amber Catford

Moths, which are important plant pollinators, are predominately active at night. Many plants that rely on nocturnal pollinators are characterised by their tantalising fragrance and brilliant flower colours. Nocturnal artificial light has been shown to reduce pollination. As a result, fewer fruits and plant seeds are produced.1 Light pollution and especially the attraction effect of artificial light plays a role in the comparatively substantial decline of moths.2 Bridge spiders like to build webs on structures near bodies of water and benefit from the insects which are attracted.3 Walnut orb-weaver spider, on the other hand, need natural darkness to build their webs.4

1 Knop E, Zoller L, Ryser R et al. (2017) Artificial light at night as a new threat to pollination. Nature 548:206‐209.
2 van Langevelde F, Braamburg‐Annegarn M, Huigens ME et al. (2017) Declines in moth populations stress the need for conserving dark nights. Global Change Biology 24:925-932.
3 Heiling AM (1999) Why do nocturnal orb-web spiders (Araneidae) search for light? Behav Ecol Sociobiol 46(1):43-49.
4 Zschokke S, Herberstein ME (2005) Laboratory methods for maintaining and studying web-building spiders. J Arachnol 33(2):205-213.

Rude awakening

© Amber Catford

Good habitat for the crepuscular and nocturnal European hedgehog includes natural, toxin-free gardens, parks or cemeteries with hedges, piles of leaves and branches, and places to slip under fences. In April, the hedgehog awakens from hibernation. Under cover of darkness, this animal uses its extremely fine sense of smell to search for insects & co. Urban hedgehogs have been shown to avoid artificially illuminated areas.1 Light pollution increases near building developments where habitats are fragmented and destroyed. Roads in residential areas are far too often a deadly trap for hedgehogs. In well-illuminated habitats, birds such as robins, blackbirds, great tits and blue tits start their morning songs earlier in the year. As a result, they also start breeding, foraging and developing earlier, which can have adverse effects on the life expectancy of the animals.2 Under laboratory conditions, it was found that a steady night-time light intensity of 0.3 lx (full moon brightness) renders male blackbirds infertile over time.3

1 Schroer S, Weiß NS, Grubisic M et al. (2019) Analyse der Auswirkungen künstlichen Lichts auf die Biodiversität. Naturschutz und Biologische Vielfalt 168. Bundesamt für Naturschutz Bonn (ed.).
2 Da Silva A, Valcu M, Kempenaers B (2015) Light pollution alters the phenology of dawn and dusk singing in common European songbirds. Phil Trans R Soc B Biol Sci 370(1667):1-9.
3 Dominoni DM, Quetting M, Partecke J (2013) Long-term effects of chronic light pollution on seasonal functions of European blackbird (Turdus merula). PLoS One 8(12):1-9.

Spring nights

© Amber Catford

Most frog and toad species are partially or completely nocturnal and have keen eyesight. The common frog is even able to perceive colours in the dark.1 Meanwhile, the common toad needs only a fraction of the light produced by the starry sky (0.00001 lx) to catch its prey at night.2 To put this value into perspective: the maximum brightness of the full moon is 0.3 lx. Nocturnal amphibians are very sensitive to glare; becoming adjusted to darkness can take more than an hour, during which time important visual information is lacking.2 Common toads move from their wintering grounds to spawning grounds in March or April. Such mass migrations are especially common between dusk and 10 pm. Common toads make use of dark passages and avoid street lighting.3 Habitat loss and road traffic are major threats to these animals.

1 Kelber A, Yovanovich C, Olsson P (2017) Thresholds and noise limitations of colour vision in dim light. Phil Trans R Soc B 372:20160065.
2 Buchanan BW (2006) Observed and Potential Effects of Artificial Night Lighting on Anuran Amphibians. In: Rich C, Longcore T (eds.): Ecological Consequences of Artificial Night Lighting. Island Press.
3 van Grunsven RHA, Creemers R, Joosten K et al. (2017) Behaviour of migrating toads under artificial lights differs from other phases of their life cycle. Amphibia-Reptilia 38:49-55.

The fox and the hare

© Amber Catford

Many sports facilities are located in natural surroundings and on the outskirts of settlements. Amongst the consequences of using sports facilities at night are the noise from operations and, in the case of ski slope lighting, even longer periods of disturbance caused by the delay in slope preparation time until late at night.1 These conditions do not suit the mountain hare, as it is predominantly crepuscular and nocturnal. Mountain-dwelling animals also have other challenges to contend with, such as climate change, which is causing high altitude habitats to shift to higher elevations, thus creating a trap for mountain hare.2 Red foxes that live near humans are predominantly nocturnal, which means that hares are likely to be on their menu. Many animals, including grouse and deer, have to manage their energy in winter due to lack of food. Disturbances caused, for example, by noise and light alter their metabolism which in turn weakens the animals.

1 Kostenzer J (2013) Leuchtende Hänge, lange Schatten – Nachtschilauf in Tirol. In: Held M, Hölker F, Jessel B. Schutz der Nacht – Lichtverschmutzung, Biodiversität und Nachtlandschaft. BfN‐Skripten 336. Bundesamt für Naturschutz (eds.).
2 Rehnus M (2013) Der Schneehase in den Alpen. Ein Überlebenskünstler mit ungewisser Zukunft. Bristol-Schriftenreihe: Vol 38.

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.