Wildlife

Terrestrial Mammals

Most Australian terrestrial mammals are nocturnal and emerge from their refuge to begin foraging at or after dusk. 99% of terrestrial mammals that are listed as threatened under the Environment Protection and Biodiversity Conservation Act in 2023 are nocturnal.

Terrestrial mammals are ground-dwelling or arboreal across different habitats and the impacts of artificial light are species specific.

Artificial light impacts on when they choose to leave their refuges, which routes they commute on and where they choose to forage. Limitations created by artificial light can affect reproductive behaviour, safety amongst predators and quantity and quality of available food and how much time is spent foraging.

Nocturnal terrestrial mammals also respond to changes in day length across seasons and changes to moonlight levels over monthly lunar cycles. Artificial light can mask these natural light changes.

The Southern Brown Bandicoot and Eastern Quoll show higher activity at half-moon than full moon. In some species, such as wallabies and rodents, this reduction in activity at full moon also leads to increased vigilance and decreased foraging, resulting in less food consumed per foraging trip and more journeys between refuges and foraging areas.

Land Birds

Natural daylength regulates the breeding behaviour and physiology of land birds. The lengthening of days in spring triggers increased production of key hormones, increase in the size of gonads, development of breeding plumage, the onset of mating song and other reproductive behaviours. The shortening of days in late summer or autumn triggers a corresponding reduction in these characteristics.

Light pollution masks natural daylength and can result in mistimed changes in birds’ physiology and behaviour, including mistimed changes in gonad size and testosterone production, early egg-laying, and early moulting. Birds in the tropics may be particularly sensitive to such changes due to the subtlety of seasonal changes in natural light.

The timing of seasonal changes may be particularly important for migratory birds that need to reduce the weight of reproductive organs (which otherwise become a burden during flight) and replace feathers before flying long distances. In Australia, such birds include migratory shorebirds and other birds that migrate to the northern hemisphere and many birds that migrate or shift range within Australia, such as the critically endangered Orange-bellied Parrot and Swift Parrot as well as many kingfishers, swallows, cuckoos, robins and silvereyes.

For migratory species the seasonal change-shifting effects of artificial light may be particularly detrimental in resting and breeding habitat areas used before or during migration. In addition, light pollution may also distract migrating birds by imitating natural sunlight or moonlight or by undermining the daily recalibration of birds internal magnetic ‘compass’.

Bird behaviour is often tightly regulated by the natural day-night cycle and by the monthly waxing and waning of moonlight. Diurnal (daytime) and nocturnal birds have different physical adaptations, such as vision and hearing, that under natural conditions allow them to co-exist by exploiting the same habitat at different times, with little overlap. Light pollution can alter this balance by extending the hours of activity and spatial distribution of diurnal birds, bringing them into contact with different prey, predators and competitors. For example, the Peregrine Falcon is a diurnal predator that can adapt its foraging behaviour to use artificial light to hunt birds at night.

Artificial light can also alter the distribution of prey and thus of nocturnal predatory birds. Insects, amphibians and birds have all been observed to cluster at light sources, and at least some owls have responded by focussing their predatory efforts around those same lights.

Disturbance of the natural day-night cycle also has consequences for birds’ sleep. Australian Magpies, Black Swans, and Domestic Pigeons, all lose sleep when exposed to streetlight-level lighting at night, although have varied sleep-recovery responses. Switching to amber lighting may reduce adverse effects on magpie sleep but does not benefit swans or pigeons.

Seabirds

Petrels, shearwaters, albatross, noddies, terns and some penguin species spend most of their lives at sea, only coming ashore to nest. All species are vulnerable to the effects of lighting.

Seabirds active at night while migrating, foraging or returning to colonies are most at risk. Fledglings are more affected by artificial lighting than adults due to the synchronised mass exodus of fledglings from their nesting sites. They can be affected by lights up to 15km away.

Seabirds have been affected by artificial light sources for centuries. Humans have used fire to attract seabirds to hunt them for food and reports of collisions with lighthouses date back to 1880. More recently artificial light associated with the rapid urbanisation of coastal areas has been linked to increased seabird mortality and today 56 petrel species worldwide are known to be affected by artificial lighting.

Artificial light can disorient seabirds, causing collision, entrapment, stranding, grounding and interference with their internal navigation. The physical aspects of light that have the greatest impact on seabirds are intensity and colour (wavelength).

Case study: Migratory shorebird, Phillip Island

Victoria’s Phillip Island is home to one of the world’s largest colonies of listed migratory Short-tailed Shearwaters (Ardenna tenuirostris). It supports more than 6% of the global population of this species.

Shearwaters nest in burrows and are nocturnally active at their breeding colonies. Fledglings leave their nests at night. When exposed to artificial light, fledglings can be disoriented and grounded. Some fledglings may reach the ocean but then be attracted back toward coastal lighting. They are also vulnerable to collision with infrastructure when disoriented, and once grounded they become vulnerable to predation or roadkill.

Phillip Island also attracts over a million visitors a year during peak holiday seasons to visit the Little Penguin ecotourism centre, the Penguin Parade®. Most visitors drive from Melbourne across a bridge to access the island. The increase in road traffic at sunset during the Easter break coincides with the maiden flight of fledgling shearwaters from their burrows.

In response to the deaths of fledglings, Phillip Island Nature Parks has an annual shearwater rescue program to remove and safely release grounded birds. In collaboration with SP Ausnet and Regional Roads Victoria, road lights on the bridge to the island are turned off during the fledgling period.

To address human safety concerns, speed limits are reduced and warning signals put in place during fledgling season. The reduced road lighting and associated traffic controls and warning signals, combined with a strong rescue program, have reduced the mortality rate of shearwaters.

Invertebrates

Most natural light is unpolarised because waves of light can ‘vibrate’ in any direction as they travel outward from the light source. However, when light reflects off a flat surface, such as a body of water, it becomes polarised because light waves can only vibrate in a single horizontal plane.

• In nature, polarised light is strongly associated with water sources, and many invertebrates, as well as other animals, use polarised light from the sun or moon to identify water bodies. Artificial light from street, vehicle and building lights often strikes surfaces that reflect polarised light, including asphalt, solar panels, window glass and even dark-coloured vehicles.
• These reflections cause invertebrates to mistake these surfaces for water, where they would normally lay their eggs. Changing artificial lighting strategies and/or the surfaces of artificial structures can reduce such ‘ecological traps’.
• Moonlight polarising in the atmosphere provides an important navigational cue for nocturnal invertebrates, including some beetles and native bull ants. As polarised moonlight cues are exceptionally subtle, they are easily disrupted by light pollution, including dim skyglow, which can disorient invertebrates and disrupt their normal movement in the landscape.
• Individual or species-level responses to artificial light amount to landscape-scale shifts in invertebrate abundance, distribution and community composition with cascading impacts on food webs, pollination and nutrient cycling.
• Artificial light disrupts invertebrate physiology, including melatonin cycles, immune function and oxidative stress. It can also disturb lifecycles at multiple points, including mating, reproduction, juvenile development, adult emergence and survival.

Each summer, on bridges across the world, mayfly massacres occur. First, warm weather prompts the transformation of the insects’ aquatic larvae. Within hours, the short-lived, flying adults pop out of streams, rivers, and lakes, eager to mate and lay eggs by the millions. But bridges illuminated with artificial light can lure the newly emerged adults away from the water to a futile death before breeding. Others, fooled by the sheen of reflective pavement, drop their eggs on the bridge road instead of the water. Because mayflies control the growth of algae and are food for fish, the fate of these humble insects may reverberate through ecosystems.

Marine turtles

• Marine turtles nest on sandy beaches in northern Australian and around the world.
• The effect of artificial light on turtle behaviour has been recognised since 1911 and observed from lights up to 18km away.
• Adult females may be deterred from nesting where artificial light is visible on a nesting beach. Moving sources of artificial (such as flash photography) may also deter, disorient or disturb nesting females.
• Females nest in higher numbers in areas that are shadowed.
• Hatchlings may become misoriented or disoriented and be unable to find the sea or successfully disperse to the open ocean.
• Hatchlings find the sea by seeing the reflections of the night sky on the water. Artificial light nearby draws them inland towards suburban, urban and industrial areas.

Bats

• Bats provide valuable ecosystem services such as pollination insect and pest suppression.
• Most of the nearly 80 bat species found in Australia are nocturnal. Because bats are adapted to the night-time environment, they are particularly vulnerable to impacts from artificial light.
• Bats can confuse artificial lighting with natural lighting cues: i.e. sunset, natural darkness, moonrise and sunrise. Natural cues influence behaviours such as roosting, emergence, feeding, torpor and commuting.
• Artificial light can affect different species in different ways.
• Bats are described as light tolerant if foraging behaviour is not negatively affected by artificial light. For example, many nationally important flying-fox camps and other known roost sites are located in artificially lit urban environments.
• Light-intolerant bats may exhibit important behaviour changes when exposed to artificial light and may actively avoid point sources of artificial light to evade predators, because of sensitivity to ultraviolet light and inability to catch prey at light sources.
• The food source of most Australian bats is nocturnal insects. Artificial light can disrupt the life cycles or habits of insects.
• Bats have high food requirements. They rest during daytime at roost sites to conserve energy for their energy-intensive nightly commute to areas where they forage for food and water.
• Bat populations are slow to recover from disruptions due to low reproduction rates.
• Any impact of artificial light on fish, plants, terrestrial vertebrates, and invertebrates an indirectly impact bats, leading to reduced growth rates, decreased reproduction and even death.
• The type of light pollution known to impact bats is artificial point source light, directly illuminating their habitat. Precautions should be taken to minimise or eliminate artificial light exposure for all bat species.