Here's How City Lights Both Attract and Repel Migratory Birds

Migratory birds regularly fly across national borders from between breeding and wintering grounds, according to Donald W. Sparling. They have flight (breast) muscles that contracts and relax as they fly for hours, which means that they rely on oxidative pathways for energy production, as reported by Science Direct.

Under the Migratory Bird Treaty Act 1918, the FWS (the Bureau of Biological Survey) is responsible for conserving migratory birds within the United States.

Their mission is to "conserve migratory bird populations and their habitats for future generations, through careful monitoring, effective management, and by supporting national and international partnerships that conserve habitat for migratory birds and other wildlife."

However, there has been a decline in the migratory birds' population lately. Most of these birds travel every night when predators are low, although the scientists are unsure how the birds can see during the night. But they observed that migratory birds are both attracted and repelled by the light pollution in the cities, so they set their eyes on making cities more livable for migratory birds.

Citizen Science Initiatives

Migratory birds passing by urban areas could get collide with buildings or get caught on to communication towers. Over the past 50 years, their population has gradually declined and light pollution cities may contribute to this loss. Scientists agree that light pollution cause disorientation to migratory birds and make it difficult for them to navigate.

However, observing and documenting the bird migration is challenging, especially at night because these species are very small, limiting the tracking devices that the scientists are using.

But thanks to the internet and other information technologies, collecting information about bird migration has become possible. Not to mention the citizen science initiatives wherein volunteers post online their observation of bird migration and the natural world. Information from them has become a valuable resource for researchers.

For example, the eBird initiative allows bird-watchers worldwide to share their observations from any location and time which produced one of the biggest citizen science databases in the world with over 922 million bird observations from 617,00 participants.

ALSO READ: Migration Pattern of Birds Are Getting Disrupted By Climate Change on a Continental Scale

Light Pollution Attract and Repel Migratory Birds

The researchers wrote in The Conversation that after they analyzed some data from eBird, they found that cities with the most number of migratory birds during spring and autumn and spring have a higher level of light pollution. That means light pollution attracts some species during migration, increasing the number of species that would normally be found in urban areas.

On the contrary, higher levels of light pollution also mean that there will be fewer migratory birds during summer and winter because of the scarcity and suitable houses in the urban areas, like large forest patches. During these seasons, migratory birds are only active during the day which creates fewer chances of attracting them to urban areas.

But the researchers also found that tree canopy cover is linked to more migratory birds during spring and summer during breeding and migration season. So the presence of trees could influence the number of migratory birds in cities.

Moreover, they also found that higher levels of impervious surface are linked to more migratory birds during winter, which could be a result of the urban heat island effect. The researchers think that the buildings, roads, and parking lots in the cities make the cities warmer than the surrounding lands, therefore reducing the cold stress on the birds and increase their food resources.