We conduct ecological assessments focusing on BAT IMPACT to ensure compliance with legal requirements and guidelines provided by the Bat Conservation Trust.
UK law protects bats from both intentional and reckless disturbance. The inadvertent placement of lighting may be deemed a criminal offence, irrespective of the absence of harmful intent.
Planning consent frequently hinges on the incorporation of bat-friendly lighting designs, considering the impact of both exterior and interior lighting on these vulnerable creatures.
INOX possesses expertise in crafting lighting impact assessments for planning, utilising our own lighting schemes or evaluating those proposed by others.
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Bats, being the only mammals capable of genuine flight, share similarities with humans - they are warm-blooded, give birth to live offspring, and produce milk for nursing. Within the confines of Britain, there are 18 distinct bat species, all of which are relatively small (with most weighing less than a £1 coin) and predominantly consuming a diet of insects.
These remarkable creatures have evolved a sophisticated echolocation system, enabling them to navigate their surroundings, avoid obstacles, and capture insects during flight. Emitting high-pitched calls while in motion, bats interpret the echoes to construct a sound image of their environment.
While some bats specialise in catching larger insects like beetles or moths, others focus on consuming vast quantities of smaller insects such as gnats, midges and mosquitoes. Bats congregate in areas abundant with insects, making traditional pasture, woodlands, hedgerows, marshes, ponds, and slow-moving rivers ideal feeding grounds.
In the winter, when insect availability diminishes, bats enter a hibernation phase. Seeking sheltered roosts, they lower their body temperature to match their surroundings and slow their heart rate to conserve energy, extending the longevity of their food reserves.
During spring and summer, female bats assemble into maternity colonies for a brief period to give birth and nurture their young, known as pups. Typically, only one pup is born each year. These maternity roosts, situated in warm and dry environments, may attract bats from a wide surrounding area. Both winter and summer roosts have specific conditions crucial for bats during those times, fostering their loyalty to these locations.
Bats exhibit an unusual longevity for their size and have a slow reproductive rate. This characteristic, coupled with their fidelity to roosts, means they return year after year. Damage or disturbance to roosts can have long-lasting consequences, as bat populations require an extended period to recover.
For additional information on bat populations, refer to https://www.bats.org.uk.
Owing to the decline in bat populations throughout the past century and recognising the crucial role of specific roost requirements in their life cycle, all bat species and their roost sites, regardless of current bat presence, enjoy comprehensive protection under both international and domestic legislation. The EC Habitats Directive, providing international safeguards, has been incorporated into national laws.
This legal framework strictly prohibits activities such as killing, injuring, capturing, or causing disturbance affecting bat populations, obstructing access to bat roosts, and damaging or destroying bat roosts. Additionally, individual bats are safeguarded from 'intentional' or 'reckless' disturbance under the Wildlife and Countryside Act 1981.
The presence of artificial lighting near a bat roost, leading to disturbance and potential abandonment, could be considered an offence against both the bat population and individual bats. Therefore, it is imperative to thoroughly assess the use of an area by bats before altering or adding artificial lighting in the vicinity of a roost, commuting routes or foraging areas.
Organisations such as Natural England, Natural Resources Wales, Scottish Natural Heritage or the Northern Ireland Environment Agency must ensure that any impacts on bats have been comprehensively assessed, and appropriate mitigation measures have been considered in mitigation license applications. These bodies also act as statutory consultees in planning applications that may impact Special Areas of Conservation, including those designated for bat conservation.
Local authorities share the responsibility of avoiding impacts on legally protected species, with impacts on bats being a vital consideration in any planning permission decision. Moreover, local authorities typically enforce specific planning policies to prevent wildlife impacts, including those on bats, within development projects.
Studies conducted in 2016 indicate that over 80% of the global population and more than 99% of the populations in the United States and Europe reside under skies affected by light pollution. This marks a significant increase from 66% in 2001, reflecting a rise of over 14%. The term 'light-polluted skies' refers to brightness levels approximately 10% higher than normal night sky levels.
In the context of England, only about a fifth of the country now enjoys 'pristine night skies’, defined as skies entirely free from light pollution. Concerns regarding the impacts of light pollution on both human and ecosystem health have been expressed for an extended period.
For bats, artificial lighting is believed to increase the risk of predation, prompting potential modifications in their behaviour as a response to this threat. The presence of various characteristics and types of artificial lighting can have diverse impacts. Different luminaire types emit varying light spectra, ranging from short wave (ultraviolet) to long wave (infrared), with differences in intensity (potentially causing glare) and illuminance (measured in lux).
Illuminating a bat roost can lead to disturbance, potentially causing bats to abandon the roost or become trapped within it. Light exposure at a roost access point can delay bats from emerging, reducing the time available for foraging. As the primary peak of nocturnal insect abundance occurs around dusk, delayed emergence can impact feeding, leading to direct consequences for bats' reproductive ecology, such as slower growth rates and young bats facing starvation. The flightpath associated with the access point is equally crucial and vulnerable, and severing a key flightpath away from the roost could induce desertion.
Artificial lighting not only disrupts bats at the roost but also influences their feeding behaviour in two ways. Firstly, certain types of light sources attract a variety of insects, including those emitting ultraviolet components or having a high blue spectral content. Secondly, illuminated conditions can act as a barrier to movement. Night-flying insect species, especially those attracted to light sources with ultraviolet components or high blue spectral content, can face challenges in the presence of artificial light. This attraction is particularly problematic in areas with a single light source in a dark environment, impacting various insects such as moths, craneflies, midges and lacewings.
Numerous studies have demonstrated that certain bat species, including noctule, Leisler’s bat, serotine, and pipistrelle bats, exhibit a tendency to gather around white mercury street lights and white metal halide lamps, utilising the insects attracted to the light as a food source. However, this behaviour is not universal across all bat species. Slower-flying broad-winged species such as long-eared bats, Myotis species (encompassing Brandt’s bat, whiskered, Daubenton’s bat, Natterer’s bat, and Bechstein’s bat), barbastelle, and greater and lesser horseshoe bats generally avoid street lights altogether. Consequently, bat species less tolerant of light face a competitive disadvantage, hindering their ability to forage successfully and efficiently, with potential significant impacts on fitness and breeding success.
The spectral impacts of light further vary; studies have revealed that Plecotus and Myotis species (slow-flying) tend to avoid white and green light-lit areas, while Pipistrellus species (fast-flying) are notably more abundant in these lit environments. However, both groups exhibit equal abundance in areas illuminated with red light compared to the dark control, offering potential options for lighting in mitigation efforts.
Moreover, it is theorised that insects are drawn to lit areas from beyond the immediately illuminated habitat, resulting in adjacent habitats supporting reduced numbers of insects - a phenomenon known as a ‘vacuum effect’. Population declines have been observed farther afield, indicating both direct and indirect impacts at play. This further impedes the ability of light-avoidant bats to feed. Notably, many of Britain’s rarest bats belong to species listed as avoiding artificial light, underscoring the potentially devastating conservation consequences of artificial lighting for these species.
The effects of artificial lighting on drinking resources for bats surpass those on foraging. White light has been observed to deter slower-flying species from drinking at cattle troughs, and even for faster-flying species, drinking behaviour is diminished, although foraging behaviour may increase.
When considering how bats navigate the landscape, artificial lighting has been shown to be particularly detrimental when used along river corridors, near woodland edges, and in proximity to hedgerows. In mainland Europe, areas frequented by foraging or ‘commuting’ bats intentionally leave stretches of road unlit, or lighting is designed to prevent bat colonies from being isolated from their foraging grounds. Continuous lighting, such as along roads or waterways, creates barriers that many bat species, especially slower-flying species, struggle to cross, even at very low light levels. Lesser horseshoe bats have been observed altering their flight paths, which connect their roosts and foraging grounds, to avoid artificial light along their usual commuting route. Significant impacts have been recorded at levels as low as 3.6 lux. Furthermore, the average light level on hedgerows most frequently used by this species has been measured at 0.45 lux.
Even bat species that have been shown to opportunistically forage in lit conditions have subsequently been found to be impacted by artificial lighting. For example, in urban areas, common pipistrelles - the UK’s most numerous species - have been observed avoiding well-lit gaps, creating a barrier effect.
During migration, green light has been demonstrated to impact not only foraging bats but also those migrating through Europe. Nathusius’ and soprano pipistrelles have been attracted to green light from a distance further than their echolocation calls reach, indicating an attraction to the light rather than insects. This illustrates a positive light attraction for these species, suggesting that limiting UV light is only part of the solution and indicating impacts from artificial light at night that aren’t yet fully understood for migrating bats. Recent studies suggest that red light also elicits positive light responses for both of these bat species during migration, surpassing warm-white light.
In summary, the impacts of artificial lighting, whether alone or in combination, are likely to have significant effects on slower-flying, rarer species and even fast-flying species, potentially affecting reproductive, foraging and roosting opportunities. On a population and ecosystem level, these impacts may influence the overall genetic pool of bat species and their prey species. Consequently, if bats are suspected to be present on a site, ecological advice should be sought, and potential survey data collected before finalising any lighting design or scheme layout.