Bats And Light Pollution: Understanding The Impact

Light pollution is a growing global issue, with almost a fifth of the world's land affected by 2001, and this has serious implications for biodiversity. Nocturnal animals are particularly vulnerable to artificial light, and bats are no exception. As well as disrupting their natural circadian rhythms, light pollution can interfere with bats' foraging, commuting, emergence, roosting, and hibernation behaviours. This can cause bats to abandon their roosts, miss out on food, and become more vulnerable to predators.

Light pollution can delay or prevent bats from leaving their roosts, reducing their foraging time

Light pollution can have a detrimental impact on bats, disturbing their natural habits and affecting their survival. As nocturnal animals, bats are especially vulnerable to artificial lighting, which can disorient them and interfere with their reproduction.

Light falling on or near a bat roost can cause several problems. It can delay or prevent bats from emerging, resulting in reduced foraging time and causing them to miss the peak time of insect abundance just after dusk. This can have a serious impact on their survival and the growth rates of their young, as all UK bats feed on insects.

In some cases, artificial lighting can even cause bats to abandon their roosts or become entombed within them, as they will be less inclined to leave when the entrance is lit. This may be considered a breach of legislation, as both bats and their roosts are protected by law in the UK.

The effects of light pollution on bats can be mitigated by keeping their habitat as dark as possible. Trees can also help to lessen the impact of artificial light, as they provide roosts, shelter from wind and predators, and better foraging opportunities.

It can cause bats to abandon their roosts

Light pollution can cause bats to abandon their roosts. Bats are nocturnal animals that have evolved to live in darkness, in part to avoid predators during daylight hours. Artificial lighting of bat roosts, access points, and foraging pathways can be extremely disturbing to bats and should be avoided.

Artificial light falling on or near a bat roost can cause many problems for bats. For example, it can delay or prevent emergence from roosts, resulting in reduced foraging time and missed opportunities to feed on insects, which are most abundant just after dusk. This can have a serious impact on their survival and the growth rates of their young.

In some cases, artificial lighting can even lead to bats becoming entombed in their roosts, as they are less inclined to leave when the entrance is lit up. This is likely to be considered a breach of legislation, as both bats and their roosts are protected by law in the UK.

The effects of artificial lighting on bats are species-specific and depend on factors such as flight morphology and performance. For example, fast-flying aerial hawking species frequently feed around street lights, while relatively slow-flying bats that forage in more confined spaces are often light-averse.

To minimise the impact of lighting on bats, it is important to keep their habitat as dark as possible. This can be achieved by reducing the duration of illumination through part-night lighting schemes or by dimming lights in specified areas. Additionally, creating dark refuges and corridors for light-sensitive species like bats can help mitigate the effects of light pollution.

It can affect the feeding behaviour of bats

Light pollution can affect the feeding behaviour of bats in several ways. Firstly, it can delay or prevent bats from emerging from their roosts, resulting in reduced foraging time and missed opportunities to feed on insects, which are most abundant just after dusk. This can have serious consequences for their survival and the growth rate of their young.

Different species of bats respond to light pollution in different ways. Slow-flying species, such as lesser horseshoe, greater horseshoe, and the 6 Myotis species, tend to avoid illuminated areas, leading to a loss of foraging grounds. This results in these slower-flying species having to use poorer-quality foraging sites and losing out on prey, which are attracted to the surrounding lit areas—a phenomenon known as the 'vacuum effect'.

On the other hand, some faster-flying species, such as noctule, Leisler's bat, serotine, and pipistrelle, can take advantage of the abundance of insects attracted to streetlights, particularly those emitting ultraviolet (UV) light. However, this also puts them at greater risk of predation, as peregrine falcons have been observed hunting bats in lit cities.

The impact of light pollution on bat feeding behaviour also depends on the type of light used. Ultraviolet (UV) light, for example, attracts more insects and consequently attracts insectivorous bats. However, all bat species studied were less active around light-emitting diode (LED) light sources, which attract fewer insects than UV lights.

The presence of trees can also influence the impact of light pollution on bat feeding behaviour. A study in Berlin found that bat activity was higher in areas with lighting and tree cover, particularly around UV lights. Tree cover provides protection for bats while also attracting insects.

Overall, light pollution can significantly affect the feeding behaviour of bats, with potential consequences for their survival and the wider ecosystem.

It can affect commuting and foraging routes

Light pollution can affect the commuting and foraging routes of bats. For example, artificial light falling on or near a bat roost can delay or prevent emergence from roosts, resulting in reduced foraging time and missed opportunities to feed on insects, which are most abundant just after dusk.

Some bat species may abandon their roosts when the entrance is illuminated, while others may become entombed. Artificial lighting can also affect the commuting and foraging routes of bats, which tend to be avoided if there is artificial light spillage in these areas.

Bats that are slow fliers and forage in confined spaces are often averse to light. These bats rely on linear habitat features, such as tree lines, for shelter from wind, rain, and predators, as well as for acoustic orientation and foraging. Using suboptimal routes to avoid artificial lighting may increase their vulnerability to aerial predators and the energetic costs associated with increased exposure to wind and rain.

Additionally, bats may have to travel further to reach foraging areas, reducing their foraging time and increasing their energy losses, which can negatively impact their reproduction rates and fitness. For example, juvenile growth rates were suppressed in the grey bat when travel distances to foraging grounds increased.

The effects of light pollution on commuting and foraging routes can also lead to competitive interactions between bat species, with light-sensitive species being excluded from illuminated resources exploited by light-tolerant species.

It can have an impact on bat reproduction and survival

Light pollution can have a significant impact on bat reproduction and survival. Bats are nocturnal creatures that have evolved to be active at night, partly to avoid predators. As such, artificial lighting can be extremely disruptive to their natural habits.

Foraging is one of the primary activities affected by light pollution. Many species of bats are insectivorous, and insects are attracted to artificial light. This can cause bats to alter their feeding behaviour, avoiding illuminated areas and losing out on prey. This can have a serious impact on their survival and the growth rates of their young. Some bat species may even abandon their roosts if the entrance is lit up, or become entombed within.

Light pollution can also affect commuting and foraging routes, which bats have been shown to avoid if there is artificial light spillage. This can lead to bats having to travel further to reach foraging areas, increasing energy expenditure and reducing foraging time. This can have a negative impact on reproduction rates and overall fitness.

The effects of light pollution on bats are species-specific, with some species more tolerant of artificial light than others. Fast-flying, edge-foraging species, such as the noctule, are more likely to benefit from the increased foraging opportunities provided by street lights. In contrast, slow-flying, forest-dwelling species, such as horseshoe bats, are more likely to be negatively impacted by light pollution, as their morphology and flight patterns make them more vulnerable to predators when flying in illuminated areas.

Overall, light pollution can have a significant impact on bat reproduction and survival, disrupting their natural habits and altering their behaviour.

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