Our disappearing darkness
Published 28 November 2023 28 November 2023
As humans have evolved and industrialised, our desire to “see” during times of natural darkness has led to night-skies that are illuminated with artificial lighting. This radical change to the night sky disrupts natural light cycles, especially in cities. This change is unprecedented and means many species, including humans, no longer experience true darkness.
Urban wildlife must adapt to survive – but what happens when, after 3.5 billion years of evolution, light invades what should be darkness?
In brightly lit environments, songbirds start singing earlier in the season and earlier each day. Wallabies are less seasonal in their reproduction, nocturnal mammals forage for less time, and the migratory behaviours of threatened species can be disrupted.
Scientists are increasingly understanding the negative impact light has on pollination, nocturnal, migratory and reproductive behaviours in wildlife such as birds, mammals, and insects.
Light is fundamental to a vast array of biological processes. For instance, variation in the intensity, duration or colour of light is linked to the vertical movement of the plankton in our oceans, the commencement of reproduction in seasonally reproducing animals and the onset of flowering and germination in plants.
In the Urban Light Lab at the University of Melbourne, these effects are being studied and they’re asking: can artificial light at night have both behavioural and physiological effects on species, and could it even drive genetic change and possibly the formation of new species?
A University of Melbourne study published in the Journal of Experimental Zoology-B, looks at questions such as these in the black field cricket, (Teleogryllus commodus) which is a nocturnal insect that lives in both urban and rural locations in Australia. The study found that exposure to artificial light at night increased the time taken for baby crickets to develop into adults. This might have implications for the insects living in urban environments as it means they reach sexual maturity later and potentially produce fewer offspring in a season.
Research also shows that animals living in our cities have disrupted sleep, increased stress and often need to adapt their behaviours to accommodate the loss of darkness. At the same time, astronomical observatories that depend on pristine, unpolluted skies are pushed further into the interior of the country.
The presence of night lighting may determine which species, or which individuals within a species, are able to thrive in our cities. Many species simply avoid the light altogether, leading to a change or even decline in the diversity of species in urban areas. Other species like moths, birds, and some bats may be attracted to the lights. For these species the lights can blind and disorient which may lead to them dying through exhaustion or because they collide with urban structures.
Some predators, like spiders or geckos, may benefit by locating themselves near lights because they feed on the attracted insects, so their next meal literally comes to them. These light related disruptions may cause some species to change. Thus, if light at night is detrimental – we would expect to see the evolution of individuals that are less attracted to light.
Ultimately, if light does affect some individuals more than others this has implications for the genetic diversity of populations in urban environments and this could make them more vulnerable to local extinction.
Associate Professor Therésa Jones who leads the Urban Light Lab at The University of Melbourne says our fundamental understanding of the ecological impact of light pollution is increasing rapidly.
“However, as our knowledge expands, we are faced with the stark reality that species do not all respond identically to light pollution and thus there is unlikely to be a 'one size fits all' solution. Thankfully, we now have the technology to adapt the intensity, colour, and duration of a light on any given night in any environment. Our next challenge is to align the interests of all potential stakeholders to ensure that we use this technology to improve ecological outcomes for all species living in our cities, including humans.”
Associate Professor Therésa Jones.
Associate Professor Jen Martin from The University of Melbourne School of BioSciences also says we are only just beginning to understand the magnitude of light pollution.
“The introduction of artificial light probably represents the most drastic change human beings have made to their environment. By measuring the light that reflects up from the earth into space, we can create light pollution maps. But these maps can’t tell us what light pollution looks like from the ground.”
Associate Professor Jen Martin.
Now a citizen science program called Globe at Night program has begun to map light pollution across Australia. The international citizen-science campaign raises public awareness of the impact of light pollution by inviting citizen-scientists to measure their night sky brightness and submit their observations from a computer or smartphone.
Marnie Ogg, the founder of Australasian Dark Sky Alliance, said information from the world challenge assisted to develop maps showing how light pollution varies across the country and even help local authorities use their darker skies as an opportunity for tourism.
“Dark sky parks and tours are already popping up around the country.”
Marnie Ogg, Founder of Australasian Dark Sky Alliance
Researchers use the data from the Globe at Night program to create a map of light pollution across Australia which will help us better understand the effects of light pollution on astronomy, people and animals.
To find out more information:
More detail on light pollution in Victoria can be found in Indicator A09 (Light Pollution) within the Air key topic.