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Dragonflies & Nighthawks Fill Chicago's August Skies

Jul 31, 2020 10:00AM ● By Sheryl DeVore

Photo by Cindy Crosby

One day in late August, Cindy Crosby stood on a bridge overlooking the Schulenberg Prairie at the Morton Arboretum. “I saw a vortex of glinting greens and blues,” says Crosby, author of the newly released Chasing Dragonflies. She was witnessing the migration of common green darner dragonflies. “I marvel at this storm of wings, this maelstrom of insects, all attuned to some wild desire,” she writes in her book. “The spectacle mostly goes unnoticed, although it’s likely been happening for hundreds of thousands of years.” Indeed, dragonflies have lived on the planet for 300 million years. Scientists first described migratory dragonflies in the late 1880s, and today believe this natural phenomenon occurs on every continent except Antarctica.

Darners and Saddlebags

“In the Chicago region, I’ve seen migration as early as mid-August and well into September,” says Crosby, who helps monitor dragonflies and damselflies for the Illinois Odonate (dragonflies and damselflies) Survey at Nachusa Grasslands and the Morton Arboretum. Just a few of more than 100 species of dragonflies seen in Illinois are migratory. “The primary migrators I see are by far common green darners and black saddlebags. You’ll usually see a few variegated meadowhawks and wandering gliders mixed in.”

Those that walk out onto a prairie or wetland, along the Lake Michigan shoreline or in their own yard during the evening can look to the sky searching for migratory dragonflies. If the green darners come close enough, observers can note the green thorax of both sexes. Males have blue abdomens and females have brownish abdomens. These are large dragonflies, with a wingspread of about four inches and a length of three inches.

Fewer numbers of black saddlebag dragonflies also fly south in fall. As this species’ name implies, they have a black saddle mark at the base of the hindwing. Females have a yellow spot toward the end of their abdomen. Although they don’t migrate in large numbers like the green darner, black saddlebags often can be seen flying overhead in ones, twos or small groups over the Chicago region.

A good day to watch hawk migration is also a good day to search for migratory dragonflies, according to Cynthia Berger, author of Wild Guide: Dragonflies. “The movements of both groups are strongly influenced by the weather,” she writes. “Look for the mass movements just after a southbound cold front passes through the area. Like raptors, dragonflies depend on thermals—rising currents of warm air—to loft them high in the air up to the altitude where steady winds will speed them on their journey south.”

Those that watch hawks at Illinois Beach State Park, in Zion, Fort Sheridan Forest Preserve, near Highwood, and the Greene Valley Forest Preserve Hawk Watch, in Naperville, often remark on the migratory dragonflies they see while documenting the hawk migration. For example, a post from the Illinois Beach State Park Hawkwatch Facebook page describes “the stars of the migration” as the common green darners. Vic Berardi, of Gurnee, founder of the hawk watch, estimates that at one point he saw roughly 1,000 of them in the sky on a late summer day.

Dragonflies migrate during the day, likely following shorelines and other long landscapes and using the sun to navigate. Why certain dragonfly species choose to migrate is a mystery just now being unraveled. Scientists do know that the dragonflies that do migrate have long wings relative to their body size, like birds, to help them maintain flight.

Research shows that green darner lifecycle is complex, and that some of them migrate while others don’t. The U.S. Forest Service Wings Across the Americas is studying dragonfly migration, and reports that the green darner has been shown to travel hundreds to thousands of miles from north to south during fall migration.

Sometimes unusually large swarms of darners have been observed; in 1992, more than 1 million were documented in the autumn of 1992 along the Lake Michigan shoreline, and in August 2015, dragonflies swarmed Grant Park during the Lollapalooza music event enough that the spectacle was deemed newsworthy.

 

Common nighthawk perched Photo by US Fish and Wildlife Service 

 

Nighthawks

Crosby and other nature lovers also look to the sky in August for migrating nighthawks.  These aren’t actually hawks, but birds that belong to the goatsucker family, which got its name from the erroneous belief that these birds sucked milk from goats. They sometimes give a nasal “peent” nasal call as they communicate with their kin.

 

Three goatsucker species are found in Illinois—the whippoorwill, which is rare in northern Illinois, the chuck-will’s-widow, a more southerly species, and th

Common nighthawk in the sky. photo by Ron Bradley

 e common nighthawk. According to the North American Breeding Bird Survey, this species’ population has declined by nearly 2 percent each year between 1966 and 2014. The decline is linked to loss of insects and habitat. Nighthawks don’t have sharp talons to snatch prey like true hawks. The only way they can feed is by opening their mouth wide and letting the food—insects, including mosquitoes—fly in.

Nighthawks nest on the ground in grasslands and open areas with soil, gravel or sand. They also nest on flat, gravel-covered rooftop. Both their natural and “manmade” habitats are declining.

Carol Kooi recalls seeing nighthawks during the summer near her northern Illinois home as a child. “I never see them anymore,” she says. Bird Watcher’s Digest editor Dawn Hewitt notes the nighthawk is imperiled in several eastern states, and is also a threatened species in Canada.

As autumn approaches, nighthawks gather in groups of tens to hundreds, sometimes more, flying over the Chicago region on their way to South America for winter. A few years ago in late August, birdwatcher Richard Biss saw roughly 1,000 common nighthawks migrating south over his Lake Villa home near a wetland.

Those that want to see the migrating nighthawks can look to the sky in August during the day and at dusk for creatures with wings that are pointed and show white bars. They seem to fly as if they are riding a roller coaster, dipping and turning to snatch insects. Sometimes they will descend low upon a large field with grasshoppers and other insects for a hearty meal.

 

Sheryl DeVore has written six books on science, health and nature. She also writes nature, health and environment stories for national and regional publications.