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Curb light pollution in your city

Why light pollution?
Why light pollution?

Light pollution is increasing globally, with an estimated 80% of the world's population currently living under a “lit sky” - a figure closer to 99% in Europe and North America. The amount of artificial light on the Earth’s surface is increasing by at least 2% annually, while the use of artificial light at night is substantially increasing all over the world. Although definitions of light pollution vary, according to the Convention on Migratory Species (CMS) Resolution 13.5 “light pollution refers to artificial light that alters the natural patterns of light and dark in ecosystems.”

Light pollution is a significant and growing threat to wildlife, including many species of migratory birds. Every year, light pollution contributes to the death of millions of birds by altering the natural patterns of light and dark in ecosystems. As a result, light pollution can change birds’ migration patterns, foraging behaviors, and vocal communication. Birds are attracted by artificial light at night, particularly when there is a low cloud, fog, rain or when they’re flying at lower altitudes. This causes migrating birds to become disorientated and potentially circling in illuminated areas. Consequently, their depleted energy reserves put these birds at risk of exhaustion, predation, and fatal collision with buildings.

Satellite monitoring revealed that from 2012 to 2016, artificially lit outdoor areas increased by 2.2% per year.  Recent studies show that this number could be much greater. 

Light pollution can change birds’ migration patterns, foraging behaviors, and vocal communication. 

What is light pollution?

As per CMS Resolution 13.5, “Light pollution refers to artificial light that alters the natural patterns of light and dark in ecosystems”. Artificial light is used to illuminate streets, commercial, residential and industrial properties, particularly in cities. Although this is often used for security, monuments, churches, bridges and other landmarks may be illuminated at night for aesthetic purposes. The increasing use of lighting has modified the natural environment dramatically, and impacts wild animals, including many species of migratory birds.

How does light pollution impact migratory birds?

Light pollution can alter birds' behaviors, including migration, foraging and vocal communication. It also affects their activity levels and their energy expenditures. Migratory birds are particularly exposed to light pollution, especially those which migrate at night. Light pollution attracts and disorients nocturnally migrating birds, which may end up circling in illuminated areas. This unnatural light-induced behavior can mean they end up depleting their energy reserves and puts them at risk of exhaustion, predation and lethal collision.

Each year, light pollution contributes to the death of millions of birds from collisions with buildings and other built infrastructure. Long distance migrants, such as the blackpoll warbler (Setophaga striata), the Asian stubtail (Urosphena squameiceps) and the oriental plover (Charadrius veredus), may start and end their migrations in areas with relatively low levels of light pollution, but during migration they may fly over areas of intense urban development where they experience high levels of artificial light. Migrating birds can be attracted to lights, particularly when there is a low cloud, fog or rain and they are flying at lower altitudes.

What can be done to curb light pollution?

International efforts are underway to reduce the impacts of artificial light on migratory species. At the last meeting of the Conference of the Parties to the Convention on the Conservation of Migratory Species of Wild Animals (CMS COP13, 2020), the COP adopted Resolution 13.5 “Light Pollution Guidelines for Wildlife”, calling for the development of new guidelines, including for migratory landbirds. A draft of these guidelines has already been prepared and is under further revision following an expert workshop that was convened in March 2022. The guidelines will ultimately be presented to CMS Parties for adoption at CMS COP14 in 2023. 

Guidelines on light pollution covering marine turtles, seabirds, and migratory shorebirds were endorsed by the CMS Parties in 2020. Among their recommendations, and particularly useful to cities, the guidelines set forth six principles of best lighting practices (see our Checklist) and call for Environmental Impact Assessments for relevant projects that could result in light pollution. These should consider the main sources of light pollution at a certain site, the likely wild species that could be impacted, and facts about proximity to important habitats and migratory pathways for different species.

Numerous cities have undertaken different approaches to curbing light pollution to protect migratory birds. These have mostly relied on creating awareness to facilitate policy changes. View our case studies here.

What can you expect from this Guide?

This guide aims to inform cities about the threats of light pollution to different species, but migratory bird species in particular. The guide also presents case studies and provides lessons learned to share knowledge and expertise across urban stakeholders to curb light pollution and protect bird species globally.