The cunning of cowbirds

Post by Jen Berlinghof

Bird migration is well underway, and the nesting season is upon us at the Lake County Forest Preserves in northern Illinois. I watched last week as an American robin (Turdus migratorius) plucked dried grasses from the yard, nudging them into place with her beak and wings, readying her cup-shaped nest for the azure eggs that are synonymous with spring. From the nearby American sycamore (Platanus occidentalis) tree, I heard the gurgling chatter of a flock of brown-headed cowbirds (Molothrus ater).

I thought about how while the robin might’ve seemed completely absorbed in her nest building, she was probably wearily listening to the cowbirds, too. Brown-headed cowbirds are North America’s most common avian brood parasite, forgoing nest building altogether. Instead, they lay their eggs in the nests of more than 200 other species of birds, leaving the incubation and rearing of their young to these unwitting foster parents.

A female brown-headed cowbird (Molothrus ater) spotted at Rollins Savanna in Grayslake. Photo © Phil Hauck.
A female brown-headed cowbird (Molothrus ater) spotted at Rollins Savanna in Grayslake. Photo © Phil Hauck.
A cowbird egg waits to hatch among "adoptive" robin egg siblings. Photo © Ted Kinsman.
A cowbird egg waits to hatch among “adoptive” robin egg siblings. Photo © Ted Kinsman.

Historically, cowbirds were commonplace only in the open grasslands of the Great Plains. They followed bison herds, and subsisted on insects flushed by these grazing beasts and seeds foraged from the ground. Yet cowbird populations have surged and expanded as human development has spread—fragmenting forests and creating a patchwork of agricultural land, as well as footholds for cowbirds to now flourish abundantly from coast to coast.

A flock of cowbirds. Photo © Greg Lavaty.
A flock of cowbirds. Photo © Greg Lavaty.

Without the burdens of nest building and chick rearing, female cowbirds have the time and energy to focus on egg production. They create as many as three dozen eggs each breeding season. While they will lay their eggs in a variety of species’ nests, genetic analysis shows that most individual females specialize on one particular host species. It’s hard to imagine, but most hosts don’t recognize cowbird eggs and chicks as different from the norm. They raise them as their own without ruffling a feather.

A dark-eyed junco (Junco hyemalis) feeds a cowbird chick. Photo © Bob Gunderson.
A dark-eyed junco (Junco hyemalis) feeds a cowbird chick. Photo © Bob Gunderson.

Cowbird development moves fast, enabling the chicks to gain an advantage at the expense of the hosts’ chicks. For starters, cowbird females lay their eggs more quickly than other birds—sometimes in under a minute—compared with the 20-100 minutes most passerines take. And cowbird eggs hatch earlier than others, making them the biggest chicks in the nest. This allows them to nudge their smaller, “adoptive” siblings out of the way when meals arrive from a parent. Cowbird chicks sometimes smother other nestlings, or even toss out the host’s eggs and smaller babies.

There are a few host species that have “cracked the cowbird problem.” They see the cowbird eggs for the intruders that they are and fight back. Larger species, such as robins, puncture or toss cowbird eggs out of their nests. Smaller species, such as yellow warblers (Setophaga petechia), that are too tiny to lug cowbird eggs out of their nests reject this role of foster parent foisted on them in a different way. They weave another layer of grasses on top of the trespasser egg, thereby preventing incubation. New research also suggests the yellow warbler’s warning call for brown-headed cowbirds might also benefit eavesdropping red-winged blackbirds (Agelaius phoeniceus), another common parasitic target for cowbirds.

Even though the cowbird adults aren’t involved with the rearing of their own young, it appears that, in some cases, they don’t abandon their chicks entirely. They keep an eye on their offspring periodically, and notice if a host removes or destroys an egg. This can trigger a retaliatory reaction from the adult cowbirds, called “mafia behavior,” in which they penalize hosts that remove their eggs by destroying the hosts’ eggs and nestlings. As it turns out, hosts are better off accepting the parasitic cowbird eggs and end up producing more of their own offspring when they do.

A male cowbird. Note the thick, conical bill. Stock photo.
A male cowbird. Note the thick, conical bill. Stock photo.

The fledgling cowbirds leave the adoptive nest about 10 days after hatching and gain independence from foster parents after about a month. At this point, they find and join a flock of cowbirds in the area and carry on their lives. Regardless of whether we humans see this behavior of brood parasitism as savvy or sinister, it has proved effective and is the hallmark to brown-headed cowbird survival.

While cowbirds have contributed to the decline of several endangered birds, such as Kirtland’s warblers (Setophaga kirtlandii) and black-capped vireos (Vireo atricapilla), they are a native species and thus protected under the Migratory Bird Treaty Act of 1918. As tempting as it may be to step in and remove parasitic eggs from host nests, taking eggs is illegal without a permit. Additionally, it’s been found that due to “mafia behavior,” and to the fact that many hosts assume the cowbird egg is part of their clutch and will have a nest-desertion response if a certain proportion of their eggs is removed, it’s best to leave them alone. Letting nature sort it all out, as with so many other facets of life, is the appropriate course.

While we’re on a bird note … if you’d like to learn the songs of migrating birds and tips to identify them, register for our FREE virtual Bird Walk and Listen programs on April 29 and May 6, 8-8:30 am.

The curious courtship of the American woodcock

Post by Jen Berlinghof

March is the demarcation of spring. This new season is brewing now as snowmelt percolates through the thick mats of leaves on the forest floor into swollen creeks. Sap is rising in the sugar maples (Acer saccharum), with its promise of sweetness after a harsh winter. The purple, mottled crowns of skunk cabbage (Symplocarpus foetidus) peek out of the thawing mud, surging toward the sun. And the quiet of winter is replaced with the cacophony of western chorus frogs (Pseudacris triseriata) accompanied by the “peent” and “whir” of American woodcocks (Scolopax minor) in the Lake County Forest Preserves in northern Illinois.

The American woodcock (Scolopax minor) is a curious species to study. Stock photo.
The American woodcock (Scolopax minor) is a curious species to study. Stock photo.
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The feathered friends of fall migration

Guest post by Ken Klick

Fall bird migration is happening now at the Lake County Forest Preserves in northern Illinois, and each day (and night) brings tens of thousands of newly arrived birds. Yet finding fall migrants can be challenging. Their subdued palettes of brown, tan, and olive feathers hide in sharp contrast to their resplendent springtime colors.

Unlike spring migration, most birds travel quietly in the fall, barely whispering a note to indicate their presence. In Lake County, fall migration starts in July, when our forests and prairies are green and full of blooming flowers. It’s a five-month-long period involving more than 200 species that rest and feed in our nearly 31,000 acres of preserves.

Spotting a bird can be difficult when vegetation conceals fleeting glimpses, making observations tricky and identification nearly impossible. Besides, who’s thinking of fall migration in July’s summer vacation mindset?

Either way, here are some of my favorite fall birding observations by month, over my past five decades of birdwatching.

July brings our first fall migrants: shorebirds. A visit to the Lake Michigan shoreline at Fort Sheridan in Lake Forest finds sanderlings (Calidris alba), sandpipers (Scolopacidae family), and yellowlegs (Tringa spp.) avoiding people and surf while searching for food. Many migrating shorebirds have just finished raising young in the tundra’s perpetual daylight and have embarked on a 6,000-mile round trip journey.

Solitary sandpiper (Tringa solitaria). Photo © Phil Hauck.
Solitary sandpiper (Tringa solitaria). Photo © Phil Hauck.
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The joy of a feather found

Guest post by Nan Buckardt

I found a feather today and it stopped me in my tracks. There it was, tucked into the dewy grass—a single, beautiful feather just lying next to my sidewalk.

It’s not uncommon to come across feathers in my work at the Lake County Forest Preserves in northern Illinois. My naturalist brain immediately started to assess the discovery, analyzing it on a few key points.

The feather the author found just outside her front door. Photo © Lake County Forest Preserves.
The feather the author found just outside her front door. Photo © Lake County Forest Preserves.
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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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Here comes the Sun (Lake)

Post by Brett Peto

The sky to the west was robin’s egg blue, a clearing in the day’s dose of clouds. They had just sneezed a handful of snow, already melting. I drove with the radio off. I didn’t know whether to wear my regular hiking boots or a pair of Wellington boots I’d packed at the last moment. The trail could be soggy, or maybe not. I was on my way to Sun Lake in Lake Villa, part of the Lake County Forest Preserves in northern Illinois.

For this month, I decided to revisit the idea behind my February 2019 post, when I explored a new-to-me preserve and wrote up my observations as a virtual tour. Readers seemed to enjoy it, and I enjoyed circling another name on the map I keep at my desk. So, here I was, about a year later, ready to chronicle another tour. Find a comfy chair and a warm mug. Here’s a snapshot of Sun Lake as I saw it.

The view looking south from the parking lot at Sun Lake. Photo © Lake County Forest Preserves.
The view looking south from the parking lot at Sun Lake. Photo © Lake County Forest Preserves.
Always look at the trail map before you go. Photo © Lake County Forest Preserves.
Always look at the trail map before you go. I walked the trail loop clockwise. Photo © Lake County Forest Preserves.
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Finding the right angle

This gallery contains 10 photos.

Post by Brett Peto

I keep thinking about angles. Not the kind you measure with a protractor, but those you measure with your mind. The angle of a story, a conversation, or a project. Photography, of course, uses physical angles—where’s the camera pointed? is the sun directly overhead or is it the sweet time of golden hour?—but the best photos make you want to see even more. They make you want to break open the frame and soak in every bit of the Lake County Forest Preserves in northern Illinois.

Since it’s nearly the end of 2019, I thought I’d turn 180 degrees and peruse the photos uploaded to our group Flickr pool since January 1. Suffice to say: we’re spoiled. Spoiled with the beauty of Lake County’s flora, fauna, and natural areas, and the talent of the photographers who capture it for everyone to see. Trees and shrubs in their bright fall wardrobes on either side of a trail draining into a vanishing point. A sandhill crane (Grus canadensis) with both wings up like a paper airplane as it dashes to take off. A whirlpool of stars spun around a rich blue sky over a tranquil wetland.

I’ve gathered these moments plus seven more below, but that’s only a small taste. I encourage you to browse the rest of the visual buffet as we make the turn out of the 2010s into the 2020s. And, hey! You might become inclined to upload that shot living on your phone, camera, or computer.

"Night Moves." Photo © reddog1975.
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Give thanks for turkey vultures

Post by Jen Berlinghof

Come late November, most of us have turkeys on the brain. But a different type of turkey is taking to the skies at this time of year on its annual migration south: the turkey vulture (Cathartes aura). You can spot them in the sky or on the ground in the Lake County Forest Preserves in northern Illinois.

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A world of warblers

Guest post by Alyssa Firkus

In my early twenties, I believed adventure was found in the tallest mountain, the deepest ocean, the largest cavern. I chased whales, orca, brown bears, bald eagles, and other charismatic megafauna. It took decades to realize I didn’t need to seek these animals or climb these mountains to find adventure. Some of the best adventure awaited me in my own backyard. This led me to join the Education Department at the Lake County Forest Preserves in northern Illinois in October 2018. What an adventure it’s been!

Anyone who’s attended a program taught by our staff or volunteers knows these educators are knowledgeable and passionate. This group ignited my latest adventure—birding—though I can’t point to a single component that sparked my newest hobby. It could have been my awe for the birders in this group, their love for birds and their impressive ability to bird by ear. It might have been my draw to a new challenge. The patience, attention to detail, and dedication it takes to be an effective birder. It may have been the rush of excitement, getting a glimpse of a rare species for a brief moment as it makes its annual migration. Perhaps all of these were feathery factors. Regardless, I’m hooked.

Birding is a rewarding activity that requires patience and knowledge. Photo © Tim Elliott.

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The wonder of wood ducks

Post by Jen Berlinghof

Spring is the starting block for wildlife in the race to find suitable mates and nesting sites. With the increased flurry in wildlife activity, staff at the Lake County Forest Preserves in northern Illinois also get an increased flurry of phone calls with questions from the public. One recent call came from a gentleman in disbelief upon seeing ducks perched in his trees. He was utterly transfixed by the phenomenon. The call brought back a flash of memory for me of the first time I saw a wood duck (Aix sponsa) as a child, on my maternal grandfather’s property in northern Illinois. Grandpa “Duck,” as we affectionately called him, was an avid outdoorsman. He spent a few moments that spring day pointing out the distinct, vibrantly hued male and the more muted female near a nest hole in an old maple tree. The pair then took off into the woods to the soundtrack of their high-pitched whistling calls.

Male wood ducks are easily identifiable by their glossy green head, chestnut breast, and other vibrant colors. Stock photo © Lake County Forest Preserves.

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