The annual fall migration of birds across the United States has continued this week, with millions of birds traversing the state of Illinois just in the last 24 hours.
According to the latest figures from BirdCast, nearly 8.5 million birds crossed Illinois between Monday night and Tuesday morning. At the peak of the migration, more than 13.5 million birds were estimated to be in flight over the state, according to BirdCast data.
In all, an estimated 840 million birds have crossed the state of Illinois since migrations began in August.
BirdCast also provides data not just on how many birds have traveled across the state, but when they do the majority of their flying during the migration season. According to that data, birds typically begin to migrate 30-to-45 minutes after sunset, with peak numbers seen approximately two-to-three hours later, usually between 10 p.m. and 12 a.m.
Birds typically are most active during the overnight hours due to cooler conditions and calmer winds.
The peak of the fall migration season typically comes in late September and early October, but some stragglers are boosting overall numbers in the state at the moment. While Tuesday night will likely be a lighter day in terms of total birds migrating, focused mainly on the Atlantic coast, Thursday could see a massive migration of birds across the central United States, including Illinois, with 276 million birds predicted to be in flight over the continental United States.
The busiest day Illinois has seen so far this year came on Oct. 5, when an estimated 57 million birds were in flight over the state.
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During periods of heavy bird migration, experts urge the public to take steps to keep the animals safe, including extinguishing unnecessary exterior lights on buildings, which can disorient birds and send them off-course. Interior lights in high-rises can have a similar effect, with companies urged to turn off lights after 11 p.m. during peak flying times.
More information can be found on the Audubon Society’s website.
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