In recent times, scientists have highlighted how artificial objects in orbit around the Earth are brightening night skies on our planet significantly more than we previously understood. Astronomers, too, have expressed their concern about the growing number of objects orbiting the planet and affecting the night skies.
But what about urban lighting? In a recent study, scientific investigators in the UK recorded the calls of migratory birds called thrushes at night. Thrushes are small to medium-sized ground living birds that feed on insects, other invertebrates and fruit. They are distributed across the planet.
In the study, the researchers found that call rates from thrushes were up to five times higher over the brightest urban areas, compared with darker villages. The findings, which were published earlier this week in the journal Ibis, the international journal of avian science, provide support to previous and ongoing research indicating that artificial light at night affects migratory birds.
As the study explains, migratory birds are subject to many pressures during their life cycle. Many are declining in population as a direct consequence. In fact, evidence from North America shows that for species that migrate at night, bright artificial light sources associated with urban areas can disrupt their natural movement patterns.
For this study, the researchers used passive acoustic recorders deployed across a gradient of artificial lighting to record the flight calls of three thrush species. “We harnessed the respective strengths of citizen science, passive acoustic monitoring, and machine learning to gather evidence of the impact of artificial light at night on migratory birds," says the study’s corresponding author Simon Gillings, PhD, of The British Trust for Ornithology. “Finding that even modest urban areas without high-rise buildings can influence migration highlights the need for improved management of urban lighting.”
The fact that the call rates were up to five times higher over the brightest urban areas, suggests a strong phototaxic effect of artificial light at night on migratory thrushes, the study explains.
With certain bird species around the world declining rapidly, the issue has picked up more attention in recent times. For instance, earlier this month, bird experts, scientists and laboratories around the world, especially in the US, urged people and organizations to turn off the lights on nights which would see significant migratory bird activity.