A thousand-mile journey on two-inch wings

Post by Jen Berlinghof

I’ve spent many days this summer living the “lake life,” from the sandy dunes of the Great Lakes to the cattail-studded coves of inland waters. The waterways found within the Lake County Forest Preserves in northern Illinois have been especially rewarding. Each shoreline has provided unique glimpses of wildlife, including an osprey (Pandion haliaetus) diving full throttle to catch a fish at dawn, and a red fox (Vulpes vulpes) pouncing on prey hidden among the beach grass at dusk.

Also present at every waterway this summer has been the jewel-hued, common green darner dragonfly (Anax junius). These ubiquitous insects effortlessly nab multitudes of mosquitoes on the wing. While the monarch butterfly (Danaus plexippus) reigns in our minds when it comes to insect migrations, recent research reveals the green darner takes a multi-generational, miles-long journey of its own each year.

Common green darner dragonflies (Anax junius) are found in the forest preserves. Stock photo.
Common green darner dragonflies (Anax junius) are found in the forest preserves. Stock photo.

Wildlife migrations are typically monitored using small tracking devices called geolocators. Songbirds and monarchs migrate in such large flocks or swarms that their travels can actually be detected by radar. But green darner dragonflies don’t usually migrate in large groups. Coupled with the fact that the technology to fit an insect weighing as little as a paperclip with a teeny transmitter is only in its infancy, scientists have faced a conundrum of how to track the marvelous migrations of these members of the Odonata order.

A video explaining how researchers revealed green darner migration patterns.

A combo of chemistry and community science provided insight into the last century of dragonfly migrations, as well as environmental impacts for future generations of flyers. Research published in the December 2018 issue of the scientific journal Biology Letters was the first of its kind to use the chemical signatures of dragonfly wing samples to describe the nearly thousand-mile journey these insects undertake on two-inch wings.

A green darner dragonfly nymph. Dragonflies and damselflies of Lake County spend the majority of their lives in this underwater stage of development—anywhere from one to four years, depending on the species. Photo © John C. Abbott & Kendra K. Abbott, Abbott Nature Photography.
A green darner dragonfly nymph. Dragonflies and damselflies of Lake County spend the majority of their lives in this underwater stage of development—anywhere from one to four years, depending on the species. Photo © John C. Abbott & Kendra K. Abbott, Abbott Nature Photography.

A record of the birth waters of every dragonfly is stored chemically in the form of a hydrogen isotope. According to the Department of Energy, isotopes are “members of a family of an element that all have the same number of protons but different numbers of neutrons.” The specific isotopes found in water vary geographically.

As swimming nymphs, dragonflies absorb the isotopes into their bodies and eventually incorporate them into the substance that forms their adult wings. Researchers extracted these chemical trademarks from hundreds of wing samples, pinpointing the general area of North America each insect originated from.

With the home bases for different darners known, migration factors had to be determined. Researchers turned to decades of community science data that suggested these dynamo dragonflies were motivated to move based on temperature and the amount of daylight.

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Areas with many dragonflies are represented in red. Areas with no dragonflies at the given point in time are represented in gray. Graphic © Matthew Dodder via Hallworth et al., Biology Letters.

The researchers determined it takes three generations of green darner dragonflies to complete the migration cycle from southern North America to the north, then back again south.

In spring, a first-generation dragonfly nymph emerges from a pond in the American South, sheds its exoskeleton, unfurls its glossy wings and flies 400-500 miles north to lay its eggs before dying. These eggs hatch and complete their metamorphosis by late summer in northern waters.

Some of this second generation will stay put, overwintering as nymphs and waiting out the cold, hunkered down like the rest of us in the Upper Midwest and Northeast. Other members of the second generation have the “travel bug” and hightail it south to lay eggs by late fall along the Gulf and Atlantic Coasts.

This third and final batch of eggs hatches over winter and the adults remain in the warm waters of the South, soaking up the sun. The eggs laid by this third, non-migratory generation will kick off the migration cycle the following spring.

Green darners are named after their resemblance to a darning needle. Photo © Phil Hauck.
Green darners are named after their resemblance to a darning needle. Photo © Phil Hauck.

As summer comes to a close, I’m still striving to live the “lake life.” I walk along the Lake Michigan shoreline at Fort Sheridan in Lake Forest and watch soaring raptors ride thermals overhead as hawk migration gets underway. Closer to the ground, green darner dragonflies zip by on their shimmering wings. Thanks to chemistry and community science, I’m keenly aware of the dual migrations that stratify the skies.

To witness green darners and other wildlife migrating, you might try our Hike Lake County Challenge, now in its 23rd year. Complete seven of the 12 designated trail routes between now and November 30, and you’ll earn a free commemorative shield or zipper pull. Bring your dog along and Fluffy will receive a commemorative dog tag for their collar! See this year’s trails.

Behind the bandit mask

Post by Brett Peto

You know them as raccoons (Procyon lotor). Though maybe trash pandas is more your style, a phrase that’s taken off since it first appeared on Reddit in 2014. (I can’t help but note the Rocket City Trash Pandas, a Minor League Baseball team, plays ball in Madison, Alabama). Or you could even know them as washing-bears, an old Germanic nickname bestowed on the species “because they have a habit of rinsing and softening their food in water before they eat it.” This moniker actually has a connection to the legendary naturalist Carolus Linnaeus, who created the Latin-based binomial nomenclature system and originally labeled the raccoon as Ursus lotor (“washer bear”). Whatever you call them, raccoons are commonly found in the Lake County Forest Preserves in northern Illinois.

It’s easy to spot one, of course, by its bandit mask: the patches of black fur bending below each of its eyes. This mask is nothing short of iconic, but it’s likely an icon with a purpose: “one hypothesis for the dark fur is that it may help reduce glare and enhance the nocturnal animal’s night vision.” There’s more to know, though, about these medium-sized mammals beyond face value—or just one feature of their faces.

A raccoon (Procyon lotor) peeks out of its tree den. Photo © John D. Kavc.
A raccoon (Procyon lotor) peeks out of its tree den. Photo © John D. Kavc.
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The solace of purple martins

Post by Jen Berlinghof

There’s solace to be found in the fact that the rhythms of nature march on. This spring, the sun still rises. The wild leek (Allium tricoccum) still pulses its verdant green arms through the pulpy leaf litter of the forest floor. The birds still surge through the skies as they migrate to and through the Lake County Forest Preserves in northern Illinois. Like us, some of these birds are inclined to congregate in large communities. Over the years, the colonies of a particular species, the purple martin (Progne subis), have become largely reliant on people to provide shelter for their nesting flocks.

Two purple martins look at each other on the ledge of a martin house. Photo © Phil Hauck.
Two purple martins look at each other on the ledge of a martin house. Photo © Phil Hauck.
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Get to know groundhogs

Post by Jen Berlinghof

Late last summer, I literally watched a groundhog (Marmota monax) fatten up before my eyes. He’d made a burrow in the field outside my office window and frequently visited the rain gardens around the Edward L. Ryerson Welcome Center in Riverwoods, part of the Lake County Forest Preserves in northern Illinois. We watched him scamper back and forth, snipping flower tops here and there, always with a mouth crammed full of flora.

Fast forward to early February, and as I look out across the same field, now dotted with small snow drifts punctuated by tufts of grasses gone tawny, I think about that groundhog curled tight in his burrow and deep in hibernation, oblivious to the hubbub of a day in his honor.

Groundhogs (Marmota monax) are active during daytime, particularly early morning and late afternoon. Stock photo.
Groundhogs (Marmota monax) are active during daytime, particularly early morning and late afternoon. Stock photo.
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Turtle Champions

Post by Allison Frederick

109 adopted turtles!

bltu-20161104-004Our inaugural campaign to enhance conservation efforts and further protect an endangered species was a huge success. Donations poured in from Lake County and beyond (as far away as California!) to adopt baby Blanding’s turtles, allowing us to continue our head-starting program and field work next summer. Continue reading

A beautiful invasion

Post by Kelsey Roehrich

I am a student at Iowa State University, and traditions are an important part of school life. One long-standing tradition centers around two swans, Lancelot and Elaine, which float on a small campus lake. Legend has it, walk around the lake three times with your significant other and you will be together forever, since it is said that swan pairs mate for life.

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