Indiana’s skies are a nighttime highway in the early weeks of May as millions of birds make the migratory passage north for their summer homes.
Herons, sparrows and buntings of all varieties fly in huge numbers over the state — as many as 10 million or more some nights. Some of them will find a summer nesting site here, but most will pause to rest on the southern shores of Lake Michigan before travelling even farther north.
The second weekend in May is when migration really peaks in the state, Whitney Yoerger of Indiana Audubon said. The number of birds starting ramping up in late April, making this a great time to get up early and witness part of the migration that goes largely unnoticed by most Hoosiers.
The first few days in May had an average of about 4.5 million birds migrating over Indiana at night, and experts predict an average of about 6 million birds passing each night through the end of May. While the nocturnal avian visitors are seldom seen, they can often be heard.
“All the bird sound in the morning is kind of this epic layering of different species,” Yoerger said. “The birds you’re finding in the trees look like they’re dripping from tree to tree because there’s lots of little flocks that are moving around and trying to catch all the insects and the natural food in the environment.”
Millions of birds already have made the journey through the state while most Hoosiers have been sleeping. One night in late April had more than 11 million birds make the journey under the cover of darkness, according to The Cornell Lab’s BirdCast. The migration dashboard tracks these numbers with radar measurements.
Why birds migrate at night
A large majority of North America’s migratory land birds, about 80%, are nocturnal migrants, Yoerger said. There are some birds, such as Blue Jays, that will migrate during the day, but the others take advantage of the winds that blow during the late-night hours.
The nighttime tail winds help play a large role in flight capacity, Yoerger explained, this saves energy for the birds and helps get them where they are going without worrying too much about predators.
While enjoying the boost from the tailwinds, birds navigate north using celestial cues from the stars and the moon during their journey. The combination of calm, cooler weather at night and their paths shone brightly by the stars give birds the perfect advantage.
Indiana Audubon nighttime bird project
To give Hoosiers an idea of the massive migration happening above their sleeping heads, Indiana Audubon kicked off it Echoes of the Night Sky project.
The effort started in the spring of 2024 to collect audio data on the flight calls birds make at night while migrating over the state. Volunteers, along with Yoerger, set up recording devices on their properties to pick up the calls while the birds fly overhead.
“It’s really allowing us to document those species that would otherwise go unseen,” Yoerger said.
Birds flying under the cover of darkness are difficult to identify, and this project allows the volunteers to analyze the visual representation of the audio data to get a good picture of what is going on overhead and see what the spring migration looks like at various points across Indiana.
Hoosiers helping birds at night
The Echoes of the Night Sky not only documents the birds flying by at night, but also helps Hoosiers connect the dots on how they can help the birds as they migrate, Yoerger said.
Indiana Audubon will send out Lights Out alerts through its social media channels to let Hoosiers know when to turn their outdoor lighting off at night.
“Lights, especially LEDs, create problems and disorients birds,” Yoerger said. “If you can be part of those Lights Outs actions, you’re doing something for the birds.”
Indiana is a crucial flyway for these migratory birds and helping them out here in some of their northernmost paths really helps them at a continental scale, Yoerger said.
IndyStar’s environmental reporting project is made possible through the generous support of the nonprofit Nina Mason Pulliam Charitable Trust.
Karl Schneider is an IndyStar environment reporter. You can reach him at karl.schneider@indystar.com. Follow him on BlueSky @karlstartswithk.bsky.social
This article originally appeared on South Bend Tribune: As you slept, millions of birds flew over Indiana. Here’s why and where they’re headed
Reporting by Karl Schneider, Indianapolis Star / South Bend Tribune
USA TODAY Network via Reuters Connect
