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This southeast Iowa forest hosts one of our most diverse woodland bird migrations, followed by a stunning summer butterfly show perhaps unequaled anywhere else in the state.
By Ty Smedes
From the May/June 2016 issue of Iowa Outdoors magazine
I’m walking a trail at Shimek State Forest’s Croton Unit, where the woodland reverberates with the music of singing Kentucky warblers—seemingly everywhere.
As the trail winds along a peaceful stream, I soon spot the black-patched face and neon-yellow body of a male Kentucky warbler atop a nearby shrub, almost at eye-level—busily consuming an insect. Closer to the parking lot, a blue-gray gnat-catcher swiftly darts onto an out-stretched branch hanging above the trail. The steely blue-gray bird conspicuously flicks its white-edged tail from side to side, to scare up insects for breakfast. But no sooner has it vacated the branch when another gnat-catcher takes its place.
Their intense interest in the branch seems too purposeful to be coincidence, and I creep closer for a better look. They’re building a nest and it’s right over the trail. Spiderwebs and lichens serve as material to build a small, compact nest, which sits on top of the branch and looks like a tree knot. It’s the middle of May and woodland bird migration has reached Shimek State Forest, with some staying to nest.
A Forest for Lumber and Adventure Escapades
Shimek State Forest in southeast Iowa’s Lee and Van Buren counties has four of its five units located near Farmington. The Keosaqua unit is near Lacey-Keosaqua State Park, which abuts the town of its namesake. The forest, named after the late Dr. Bohumil Shimek, a University of Iowa professor and one of Iowa’s early conservationists, saw its first commercial sales of sawtimber and other lumber products in 1972. Since that time, the forest is also managed not only for forest products, but wildlife habitat, erosion control and watershed protection. Plus, fun abounds here as the deep forest is a haven to hunt, fish, camp, hike, picnic and enjoy the outdoors.
A Migration Hot-Spot for Woodland Birds
On another visit I run into well-known Burlington birder Chuck Fuller. The spring bird migration brings him to Shimek’s Donnellson, Farmington and Croton units several times each week.
“My mother learned birding on her own, and her influence started me on the road to birding 50 years ago,” Fuller recalls. “I initially visited Shimek with my friend Bob Cecil, about 20 years ago, on a quest to find the elusive worm-eating warbler. I love the Donnellson Unit and always look for pine and hooded warblers there. But the Croton Unit is my favorite, because it’s the most productive.”
He says Croton has changed through the years, and the birds move as the habitat changed.
“I’ve gotten to know Croton well over the years and the species that use it,” says Fuller, who looks for worm-eating, cerulean and hooded warblers there and is quick to note many other woodland species at Shimek—summer and scarlet tanagers and the much sought after white-eyed vireo.
The next morning, I bump into Karen Viste-Sparkman and her husband Stuart while birding in the Croton Unit. They are enjoying a long weekend of birding, which included a Friday stop exploring the hills and forests at Lacey-Keosauqua State Park, as well as the Shimek units located near Farmington on Saturday. Like Fuller, they also visit the Croton Unit because of the reliability of finding worm-eating warblers, as well as yellow-breasted chats, hooded warblers and white-eyed vireos. They recommend walking the western side of Croton, beginning at the intersection of Belfast Road and 150th Avenue northward for about a half-mile.
Karen recounts once seeing a pileated woodpecker land close by, with Stuart eyeing a number of bird species all along the road which runs adjacent to a creek. They rely a lot on “birding by ear,” which means they are experts at identifying a bird by its call or song, but which can’t be seen. Stuart laughingly recalls hearing a Connecticut warbler “that seemed to sing and move all around them,” which they never caught sight of. It’s a valuable skill to identify birds by their vocalizations, especially in dense forest where birds can go unseen in the leafy canopy and wooded understory.
On the Trail for Iowa’s Rarest Woodland Birds
Only a few yards farther down the trail I spot a large warbler with greenish back, strikingly yellow breast and gray face—accented with a prominent white eye-ring. It’s a yellow-breasted chat, North America’s largest warbler, and an uncommon Iowa nester. The chat is of great interest to Iowa birders, and those who venture here in May have an excellent chance of spotting one in Shimek’s Croton Unit. Many birds such as the chat need large forest tracts for successful nesting and experts agree that probably 10 species of woodland warblers (or more) nest here.
Some of Iowa’s Best Butterfly Diversity
Solon butterfly expert Chris Edwards considers the greater Shimek area—state forest land as well as nearby roadsides—among the top, if not the best, butterfly habitat in eastern Iowa.
“There are several reasons for this,” says Edwards. Large blocks of natural habitat exist—all located in extreme southeastern Iowa. That’s important as butterfly diversity generally increases as one travels farther south in Iowa. “Finally, it’s readily accessible public land with good roads and, in some areas, trails,” he says.
Edwards conducts three Fourth of July Butterfly Counts annually in Iowa City and Shimek and Yellow River state forests.
“I started the Iowa City count in 1999 and have done the Shimek and Yellow River counts annually since 2001. Sometimes I conduct counts alone, and other times I’m joined by friends or acquaintances who share my interest in butterflies,” he says.
“As a child I was always interested in nature, birds and animals thanks to the influence of my maternal grandparents. When I was 8, I spent a magical summer chasing and collecting butterflies in the woods and fields near my home. Then I moved on to other things. About 25 years later I spent a lot of time outdoors birding, and that led to a renewed interest in butterflies. I joined the North America Butterfly Association and learned about the count program, and since I enjoy ‘citizen scientist’ projects, it was right up my alley.”
Edwards says the North America Butterfly Association (NABA) sponsors a Butterfly Count Program, which includes spring seasonal counts, Fourth of July counts (which occur anytime in June or July) and fall seasonal counts. The counts are similar to Christmas bird counts in that participants find, identify and count all the butterflies they can within a 15-mile diameter circle, at approximately the same time each year.
“I’ve found about 70 butterfly species in the Shimek area, either in the state forest itself or along nearby roadsides,” he says. (For comparison, during 17 years of statewide observation I’ve seen 90 butterfly species.) About 120 species are known to occur in Iowa.
Rare resident butterflies at Shimek include pipevine swallowtail (a very healthy population), harvester, Henry’s elfin, Hayhurst’s scallopwing and Zabulon skipper. Rare southern strays include zebra swallowtail, spicebush swallowtail, sleepy orange and goatweed leafwing. One may get lucky and observe the state-threatened Byssus skipper on the prairie at the Donnellson Unit.
Edwards finds the best numbers and diversity along the roadsides at the Croton and Donnellson units. Roadsides tend to have more butterflies because they’re attracted to the many native (and some non-native) flowering plants along the roads. Many forest butterflies also venture out to gravel roads to obtain minerals in puddles or damp spots. Streams and stream corridors through the forest also attract butterflies for the same reasons. Although most of the state forest habitat is woodland, the Donnellson unit also holds a large reconstructed prairie which is good butterfly habitat, too.
When and Where to see butterflies
Edwards says butterflies can be observed at Shimek from April to October, with different species appearing at varying times, but peak numbers and diversity occur mid-June to mid-September. The best conditions for observation are warm, sunny days, with peak activity generally between 9 a.m. to 5 p.m.
“Butterflies are less active in cool, cloudy and especially rainy conditions,” he adds.
Changes in a forest or to bird or butterfly populations can happen suddenly or gradually over time, and often go unnoticed to most citizens. But for those with keen eyes and years of experience, they tell a different story. Unfortunately, from birder Chuck Fuller’s practiced eyes, “Over the years I’m seeing fewer days with big numbers of birds, compared to when I started birding.”
And that is just one reason why bird and butterfly counts are vital—to help track subtle changes over time. Not only are they an adventurous way to get outside and spot colorful species, they can also yield some unexpected stories.
“On my Shimek survey last summer,” says Edwards, “I was walking along a roadside looking for butterflies, when a Lee County deputy sheriff drove up and politely asked what I was doing. Satisfied with my response, he wished me well and sped off. Since I’ve never seen a sheriff’s vehicle along this out-of-the-way gravel road, I’m sure a local resident was concerned I was up to no good and requested a drive-by. I would have liked to have seen their expression when they got the call back from the sheriff’s office—“What? He’s counting butterflies???”
Perhaps we need more naturalists like Fuller, Edwards and the Sparkmans, out there surveying
birds and butterflies, so those survey results and their visibility to the public draw attention to our
often diminishing wildlife populations.