It’s a quiet night right on the edges of London. Apart from the tarmac roar of the distant A40, only the languid ripples of a river and the whispering swish of mature alders and willows break the silence under an almost cloudless, ultramarine sky. There are six of us, well wrapped-up even though it’s June, slowly ambling up a wooded track, and we’re hoping to witness a rare sight in the capital. Then, almost out of nowhere, a soft greenish fluorescence – like a tiny cat’s-eye – shimmers into view. This is bioluminescence in action: a glow-worm trying to attract mates in the gloom. Glow-worms are beetles, and the light emits from the larviform females’ ¹ abdomens through the oxidation of a chemical with the devilish name of luciferin.

Over 13,000 species of fungi, plants and animals, most of which are wild, have been recorded in London.

Over in the Lower Lea Valley, some 15km away, another group of nocturnal wanderers is searching alongside a reservoir against an orangier sky. The volunteers have small boxes in their hands, mostly held aloft, and a couple also carry torches or smart phones on full beam to help them navigate their way. Every so often the boxes stutter out a crescendo of clatter-clicks, causing little, hushed whoops of delight – for they are picking up the sonar calls of bats, usually pipstrelles, but also noctule, Daubenton and Leisler’s bats, as they seek moths and midges over the water’s edge.

Whether it’s the light pulses of glow-worms or the pippity-clicks of bats, most of London’s nightlife goes unnoticed by humans. We are large diurnal mammals, evolved to be active during the daytime, with good daylight vision but pretty limited hearing and sense of smell. So it takes effort by intrepid naturalists to get a picture of how most nocturnal animals behave, how they navigate an increasingly-lit London, and how best to design and manage our city to give them the room to flourish.

A lively night indeed

London is rapidly moving towards becoming a 24/7 city. The opening of several tube lines as all-hour services over the summer is the latest of many steps that began with changes to shops and licensing laws back in the 1980s that are changing the city’s night and, with it, our cumulative impact on the capital’s wildlife. With an increased focus on the night-time economy, what are the implications for the wildlife with which we share our city, but which has different nocturnal rhythms and needs to our own?

Over 13,000 species of fungi, plants and animals, most of which are wild, have been recorded in London. A significant proportion of these are crepuscular – active during dusk – or nocturnal in their habits. For example, most mammals are active during the night – including the eight species of bat recorded in London, shrew, mole, hedgehog, bank vole, wood mouse, stoat, badger, fox, and the four species of deer – which is why they remain elusive, apart from their mating calls or, in the case of fox and badger, the disruptions they may cause to some litter bins or gardens. Deer, while commonly seen in herds during the day, use darkness to break cover and feed. The muntjac, a small dog-sized deer native to China, which escaped from Woburn Park in about 1925 and is now widespread in many of London’s outer boroughs, has a characteristic call, usually heard only at night, giving it its other name – barking deer. One herd of fallow deer has become much bolder: they regularly wander around an estate in east London, almost oblivious to the cars and night buses; photographs showing them silhouetted against the warm yellowing street light glow offer an amazing juxtaposition of the wild and the city.

Amphibians are nocturnal, as are a number of fish, notably European eel and stone loach. Some key groups of invertebrates are active during the night: famously moths, but also lacewings, ground beetles, rove beetles (including glow-worm), silverfish, spiders, centipedes, earthworms and many molluscs. And while the four species of owls residing in London – tawny, barn, little and short-eared – are famously associated with nocturnal habits, they’re not the only birds active in town overnight: blackbird, song thrush, robin, blackcap, snipe and woodcock are just a few of the birds that don’t necessarily settle at sunset. Nightingales may never have sung in Berkeley Square, but along the River Crane in Twickenham you may hear the loud chorus of the marsh frog, a species first introduced to the country in the 1920s on Romney Marsh, whose nocturnal calls can be surprisingly loud, especially in early spring; and which, if not exactly mellifluous (they’re more of a rasping burble) have led to their being known as marsh nightingales.

In reality, we don’t know exactly how nocturnal species are responding to London’s nightlife, as so many are under-recorded. It is only comparatively recently – with the development of bat box technologies – that we’re beginning to get an insight into bats and their behaviour in London. For many other species, our information is based on anecdotal evidence or inferred from research conducted in cities elsewhere in the world.

A recent report suggests that there are now fewer than a million hedgehogs left in Britain, down from 36 million in the 1950s and an estimated 2 million in the mid-1990s.²) Given that the hedgehog was voted Britain’s favourite animal in 2013, it is somewhat ironic that we are inadvertently making life so difficult for them in our cities. An insectivore associated for much of the 20th century with London’s parks, gardens and woodlands, the hedgehog has become increasingly scarce across much of the capital. A small population in Regent’s Park may now be the only colony left in central London (and is vulnerable to a lorry park being proposed for HS2); elsewhere, hedgehogs are increasingly only found in the outer suburbs – although comprehensive data is lacking. Changes to gardens and the poisoning of hedgehog prey through pesticides have undoubtedly had an effect, but so too have our roads, which are just too dangerous for them. And the growth of late-night traffic is clearly influential given their nocturnal behaviour.

It is very likely that an ill-planned but vibrant night-time economy, with its attendant lighting, increased traffic, noise and fireworks could lead to ruin for much of our nocturnal wildlife. So as we learn more about how these species use London between dusk and dawn, we should put in place measures that minimise harm and allow them some space under dark skies.

All day and all of the night?

As long ago as 2003 the night sky above London was described as 91 per cent light-saturated. Transport corridors have long been sources of light pollution, but sports grounds (now often used well into the night), illuminated advertising, and security lighting are increasingly affecting nocturnal wildlife, disrupting natural patterns of light and dark and disturbing invertebrate feeding, breeding and movement – potentially reducing and fragmenting populations.

Along the River Crane in Twickenham you may hear the loud chorus of the marsh frog, a species first introduced to the country in the 1920s on Romney Marsh.

Some invertebrates, such as moths, are attracted to artificial lights at night. As many as a third of flying insects attracted to external lights will die as a result of their encounter; they can also become disoriented and exhausted, making them more susceptible to predation. In addition, the polarisation of light by shiny surfaces attracts insects, particularly egg-laying females, away from water. Reflected light has the potential to attract pollinators and impact on their populations, on predators and on pollination rates. Many invertebrates’ natural rhythms depend upon distinguishing day and night, along with seasonal and lunar changes, and can be adversely affected by artificial lighting levels.

British bat species have all suffered dramatic reductions in their numbers in the past century, and for this reason are now afforded levels of legal protection from disturbance. Light falling on a bat roost exit point will (at least) delay bats from emerging, which shortens the amount of time available to them for foraging. As the peak of nocturnal insect abundance occurs at and soon after dusk, a delay in emergence means this vital time for feeding is missed. At worst, the bats may feel compelled to abandon the roost where they shelter and breed. Bats are faithful to their roosts over many years and disturbance of this sort can have a significant effect on the future of a colony. Excessive lighting can breach the national and European legislation that protects British bats and their roosts.

In addition to causing disturbance at the roost, artificial lighting notoriously influences the feeding behaviour of bats and their use of the foraging routes along which they hunt. But it’s not a simple picture: some species are attracted to lights because they attract their prey, while others avoid it. Many night-flying species of insect such as moths, midges and lacewings are attracted to lamps that emit short-wavelength light. Noctule, serotine, pipistrelles and Leisler’s bats take advantage of the concentration of insects around white streetlights as a source of prey but the slower flying, broad-winged species, such as long-eared, Daubenton’s, and Natterer’s bats generally avoid external lights.

The spectrum of light used – as well as the move from sodium and halogen lighting towards light emitting diodes (LEDs) – is as influential as brightness and location. A recent German study has shown that the replacement of conventional bulbs in street lighting by energy-saving LEDs has considerable influence on bats. Opportunistic bats – such as those adapted to hunting light-attracted insect prey – lose hunting opportunities, while light-sensitive species benefit. Lighting can also be harmful if it illuminates foraging habitats used by bats, such as river corridors, field hedgerows and woodland edges. Studies have shown that continuous lighting along roads creates barriers that some bat species will not cross.

On a quiet night you might hear the soft high-pitched ‘seep-seep’ contact calls of redwings carry across the night sky.

Birds, too, are affected by light. Many years ago, when I was responsible for the trees and greenspaces of a social housing landlord, I was asked by some residents to cut down a line of trees because of the birds that sang in them. “Can you fell all them trees, please? The birds keep us awake all night because of their bloody singing…” Here was a sign both that nature disrupts our night-time habits and that our nocturnal behaviours are increasingly disrupting nature.

Birds are governed by the 24-hour cycle – the circadian rhythm – of day and night: the onset of the dawn chorus is triggered by a combination of the birds’ internal clocks and the very first rays of sunlight. Even low light intensities can trigger song in some birds and, because they continue singing until dusk, the singing period can easily be extended into the night if lighting is of sufficient intensity.

The robin is the most common night-time songster in London. Research suggests that city lights convince many birds that there is no end to the day. Robins are adapted to hunting insects in dim light, so may be particularly sensitive to the effects of artificial lighting. Blue light from neon signs, in particular, is especially disruptive to birds’ circadian rhythm. The reasons for the robins’ nocturnal singing have been a subject of some debate, however, and there is another view that the birds predominantly sing at night in urban areas because it is too noisy during the day. In order to be heard against the din of traffic, they have adapted to attract their mates and defend their territories with more crepuscular choruses. While singing through the night takes up a lot of energy, research has shown that it does not appear to have a significant effect on the birds’ body mass regulation. But the continual lack of sleep is likely to be detrimental to the birds’ survival and could disrupt the long-term circadian rhythm that dictates the onset of the breeding season.

Smarter lighting, darker skies?

Many species of bird migrate at night. During autumn, flocks of thrushes – redwing and fieldfare – migrate from Iceland and Scandinavia, navigating by the stars. On a quiet night you might hear the soft high-pitched ‘seep-seep’ contact calls of redwings carry across the night sky. But birds can easily be disorientated by lights; there are well-documented cases of the mass mortality of nocturnal migrating birds as they strike tall, lit buildings. In October a woodcock was found stunned at the bottom of City Hall and many warblers are found dead at the foot of some of Docklands’ skyscrapers each spring. Chicago stands in the middle of a very important migratory highway along which five million birds, 250 species, fly twice a year. In 2000, the City’s Department of the Environment estimated that tens of thousands of birds were killed from night-time lights each season and initiated the Lights Out programme, encouraging building managers to dim or turn off decorative lighting late at night and to minimise the use of interior lights during the migration season. The initiative has subsequently won the support of almost all of the major skyscrapers in Chicago. Such a programme has yet to take flight in London.

Skyglow – the orange ‘halo’ over towns and roads – prevents us seeing the stars: in many parts of London much of the stellar skyscape is obliterated. Astronomers and countryside campaigners have established the Dark Skies Campaign and awarded six ‘dark sky parks’ in Britain, the most recent – and nearest to London – in the Elan Valley in Wales. While no part of London can match these, there are still significant tracts where the night sky remains more ultramarine than orange, and perhaps these need protection from development.

There are positive trends in development and urban design: lower light that is easier to control (for when it’s really needed) and is both more energy efficient and more sensitive to its impact upon bats and birds; more specific directioning; better shades; and bulbs of specific spectral range and luminosity. These strategies can be required as planning conditions to meet concerns about impacts on biodiversity. Nevertheless, there are still major attitudinal assumptions about lighting, especially in terms of safety, security and traffic navigation (i.e. the brighter the better) that can make it difficult to balance the needs of people and wildlife in the city.

Crosstown traffic

Although traffic volumes have been falling steadily since their peak in 1999, London is still a city of cars. Reliable statistics about night-time road use are few: anecdotally, it has risen significantly over the past 30 years as demand has approached capacity in the daytime peaks, leading drivers increasingly to choose to travel at off-peak times, aided by opportunities for leisure and flexible working. These dampen the traffic peaks and spread the ‘busy-ness’ of roads: earlier in the morning, later into the night.

Some birds are known to avoid noisy areas as they cannot hear song to mark out territories or attract mates.

Traffic levels inevitably have an impact on animals that naturally wander. Tens of thousands of hedgehogs are killed by road traffic in the country each year; in London, where hedgehog habitat is fragmented, ever-smaller populations can become isolated and vulnerable to local extinctions. But the full picture is not known, and further research – which London Wildlife Trust is keen to pursue – is required to gain better insight as to how hedgehog populations can remain viable given the increasing traffic levels on our roads.

Noise too, has an effect – not only the sound of traffic, pubs & clubs, but also of construction, as the demands for infrastructure require 24-hour delivery programmes (with the lighting and disturbance that accompanies it). In many cases the worst impacts are local and temporary, and legislation is in place to limit or manage them.

Opening our eyes and ears

As London has moved to become ever more busy into the night, so our interest in the city’s nocturnal wildlife has – perhaps paradoxically – grown. Over the past 20 years I’ve witnessed an incredible explosion of interest in bats. This summer at Woodberry Woodlands, Bat Conservation Trust and London Wildlife Trust co-hosted BatFest to raise awareness of bats and their conservation needs. There’s much to do still to counter bats’ poor public profile (vampires and all that), but also to relieve the pressure created by modern construction squeezing out the spaces they can use to roost (a pipistrelle needs only an 8mm gap), and the loss of habitats on which they depend for food.

This is where the work of organisations like London Wildlife Trust, London Bat Group, and local ‘friends of parks’ groups are so important in championing the needs of the city’s nocturnal biodiversity, from moths and lacewings to pipistrelles and hedgehogs. There are some exciting sonar and sensing technologies evolving that could help us better design and manage the city for them into the future, but there is a need for political acknowledgement that the night is a time for wildlife too. London is already buzzing at night and it will undoubtedly get busier. Wildlife already faces acute pressures in this rapidly growing city; making sure we don’t over-brighten the night would be a step in the right direction.