Effect of Light Pollution on Migratory Birds

Every year different species of birds come from different locations in the world. They cross 1000 km of distance to reach the best environmental conditions to nurture their entire community. Also looking for a habitat to breed and raise their young ones.  There are 10,000 bird species around the world, out of which approximately 1,800 are long-distance migrating species. In 2020, scientists had recorded the longest ever known migratory flight of more than 7,500 miles across the Pacific Ocean between Alaska and New Zealand for nonstop 11 days. 

In spite of so much research being conducted to date, it is not completely understood the pattern of the path followed by migrating birds.

The following pattern has been observed:

• Huge flocks of birds migrate to southern wintering areas from northern breeding grounds.
• Southern parts of Africa become a breeding ground for some birds while many migrate to northern wintering grounds.
• Some can be seen coming to tableland during winter and vice versa moving higher up to a lofty mountain in summer.

Many ancient Greek authors have mentioned in their books, the migration of bird species like storks, turtle doves, and swallows. Various migration patterns have been noticed. It is most commonly observed that migratory birds fly to regions with favourable breeding conditions, from the unsuitable climatic conditions that arise due to low temperatures. In fact, for centuries, in almost all cultures such arrival of migrating birds is believed to signify the beginning of spring and the rebirth of nature. That’s why traditionally these flocks of birds are considered a messenger of new birth or of peace and hope.

How do Migrating Birds Travel such a Long Distance?

Recent experiments indicate that they adjust their flight with the Earth’s magnetic field and the light receptors in their eyes aid them.
Earth’s magnetic field acts as a compass, which directs them to the location. The research tells that the routing sense and signals function via the ‘magnetically sensitive proteins’ called ‘cryptochromes’ found in their retinas enable.

Various studies have been conducted where the connection has been established with light received by these migrating birds. 
One research says that as the season change approaches the light photoreceptor cell in the retina rises. This further stimulates cryptochromes and produces chemical reactions, which signal the direction in relation to the Earth’s magnetic field.  
However, so many difficulties they face during their long journeys like inadequate food, collisions with windows, buildings, power lines, Light, network towers, and poor weather.

Artificial Light has adverse Effects on Migrating Birds:

The unavoidable light pollution of the city disrupts their flyways and is hazardous for them. The rising city’s artificial light is becoming one of the principal causes of migrating birds’ fatal collisions.

Almost 80 percent of the world’s population is covered under artificial light. While in Europe and North America the percentage is as good as 99 per cent. During the period from 2012 to 2016 through Satellite, it was found that artificial light in outdoor areas had increased by 2.2 % each year.

When the collective city light outshines like a constellation it disorients the passing migrating birds from their migration path. As it interferes with the light photoreceptor cell in the retina and obscures the magnetic compass of the birds. The confused birds get pulled toward the source of light and throng around it, and during the process majorly lose their energy reserves. As they come very close to the ground, either they become prey for housecats or collide with surrounding windows or buildings. 
Artificial lights are so harmful that it not only interferes with the migrating bird’s ability to navigate, but also disrupt their immune systems, microbiomes, foraging behaviour, and sleep cycles.

Artificial light at night (ALAN) causes Light pollution as it reaches into the airspace, and scatters light in the atmosphere. Over years it has increased so much that under these lights spread across the sky Milky Way is no longer visible clearly to Human eyes.
Not only migrating birds, but it has resulted in many medical health issues in humans also like breast cancer, reduced skeletal muscle, sleep disorders, gastrointestinal illness, mood swings, and cardiovascular disease.

Solutions for Light Pollution to Safeguard Migrating Birds:

Plenty of research has been conducted to protect the birds from losing their migrating flyways. It was observed that birds get disoriented because of the red and white light as it has long-wavelength radiation. While blue and green light doesn’t distract migrating birds as much because of its less or short wavelength. Therefore, the following measures can be considered:

1. The light radiation wavelength aspect can be used to develop bird-friendly artificial lighting by adjusting the wavelength feature of the light. Although the experiment proved optimistic, however, its impact on other species needs to be investigated.
2. Generate awareness to use only covered bulbs facing downwards. A low-glare light should be widely used by people. Turn off the lights when it is not required. Thus, Dimmers, motion sensory lights, and timers can definitely reduce the light dispersed across the sky and save energy.
3. It is found that the coloured lights are anti-glare and can be used for night lighting. However, avoid blue or white lights at night as they glare more and blur human vision. Also adversely affects migratory species.
4. Automatic systems for street lights at certain times of the day, which can switch on and off the light as per the requirement.
5. Further to reduce energy and glare LEDs and compact fluorescents light (CFLs) should be used primarily. But only warm-coloured bulbs are to be used.

Our efforts and systematically planned artificial light infrastructure can save the life of 1000s migratory birds, who occupy a special beautiful place almost in every culture and tale. The World Migratory Bird Day 2022 theme was Light Pollution. It was celebrated on 8th October to build awareness about the adversities faced by migratory birds during their flyway. And also to implement ways to protect them.

Importance to Save Migratory Birds:

Migratory birds are highly Indispensable for our Ecosystems.

1. Such birds work as pest control agents, by consuming insects and other organisms that are harmful to the environment and crops. For example, a Locust attack can prove disastrous if their numbers grow by an enormous proportion.
2. Along their routes during migration, they disperse seeds, thereby helping in the maintenance of biodiversity.
3. The Migratory Ducks gobble fish eggs and if they survive in their gut, it drops out of ducks’ excrement onto the new water bodies. Thus they also offer a new species to the migrated region. 
4. The droppings of the birds, are rich in nitrogen, calcium, and other minerals. It is also utilized as an organic fertilizer. 
5. Every season, Migratory birds play both prey and predator roles in ecosystems. It helps balance the environmental requirement of an area.

For centuries they have been a source of entertainment for bird watchers across the globe. In some parts of the world every year, bird lovers built spaces in their houses and keep food to invite migratory birds to their homes. These birds coming to their home or region is regarded as an auspicious event.
As per Secretary-General of the United Nations António Guterres, “Migratory birds connect people, ecosystems, and nations. They are symbols of peace and of an interconnected planet. Their epic journeys inspire people of all ages, across the globe”. To address light pollution many global governments and communities are working together on the guidelines under the ‘Convention on the Conservation of Migratory Species of Wild Animals‘ (CMS). The CMS Conference 2020 had already set guidelines addressing the impact of light pollution on marine turtles, seabirds and migratory shorebirds. The new light pollution guidelines will be presented at the upcoming 2023 CMS Conference.  It includes a wide range of measures some of them are avoid spillover of artificial light, use non-reflective lights with reduced or filtered harmful wavelengths, and encouraging adaptive light controls to manage light timing, intensity, and colour.