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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On the path to recovery

Editor’s note: hello readers, Brett Peto here. Guest author Pati Vitt, Manager of Restoration Ecology at the Lake County Forest Preserves in northern Illinois, is back with the second of her three-part series about our research project to restore 180 acres of former farmland within Grant Woods Forest Preserve using a climate-adapted, regionally sourced native seed mix.

An aerial view of the 180-acre research project area at Grant Woods in Ingleside. Photo © Mike Borkowski.
An aerial view of the 180-acre research project area at Grant Woods in Ingleside. Photo © Mike Borkowski.
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Flicking through the Flickr pool

This gallery contains 10 photos.

Post by Brett Peto

You don’t need me to tell you that 2020 has been a long year. In a pandemic, separated from routines, sometimes days go slow but months go fast, and vice versa. There are fewer anchors around which to pin our schedules like so many pieces of laundry on a clothesline. Some people have started baking homemade bread, assembling model kits, binging movies and podcasts, devouring piles of books, or playing long-distance board games over Zoom. Our strategies may vary, but I think it’s helpful to have as many coping mechanisms as we can gather this year.

One adopted or continued by many folks is spending more time outdoors. Whether in yards, neighborhoods, parks, or the Lake County Forest Preserves in northern Illinois, people are discovering or rediscovering the value of nature, even as the thermometer dips. Fresh air; sunshine; wide horizons; the sounds of wind in trees and water over rocks; birds and squirrels and foxes living their private lives; the calm curiosity to find out where a trail goes and the confidence that it’s designed to go somewhere.

"Ice Ice Baby." Photo © Michelle Wendling.
“Ice Ice Baby.” Photo © Michelle Wendling.
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Growing through change

Editor’s note: hello readers, Brett Peto here. This month, we’ve opened up the floor to guest author Pati Vitt, Manager of Restoration Ecology. She’s here to discuss a recent virtual workshop we held as part of our research project to determine best seed sourcing practices for climate resiliency.

“We know that by 2050, our climate is predicted to be more like Oklahoma,” says Pati. So, we need to understand whether we should source seeds from further south to make our restoration projects more resilient to climate change. To help determine this, we’re procuring 800 pounds of native grass seed from southern Illinois and Kentucky.

This November, we’ll plant those seeds in 180 acres of former agricultural fields at Grant Woods in Ingleside. Then we’ll monitor and compare each species’ growth to seeds sourced from our area. I’ll let Pati pick it up from here.

A portion of the research project area at Grant Woods. Photo © Lake County Forest Preserves.
A portion of the research project area at Grant Woods. Photo © Lake County Forest Preserves.
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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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Milkweed. It’s not just for the monarchs.

Post by Jen Berlinghof

Being home more these past months has allowed my family copious time to observe the common milkweed (Asclepias syriaca) in our garden go through its life cycle day by day. We’ve witnessed the transformation from wily little sprouts in early summer to blooming beasts, with pompoms of eraser-pink flowers wafting perfume across the yard—even threatening to take over the footpath—by Fourth of July. Now in the sweet days of September, our milkweed is laden with swelling seed pods, ready to burst with floating seeds like so many little white parachutes scattered in the autumnal sky. The situation is similar in many of the Lake County Forest Preserves in northern Illinois.

The beautiful flowerhead of common milkweed (Asclepias syriaca). Photo © Lake County Forest Preserves.
The beautiful flowerhead of common milkweed (Asclepias syriaca). Photo © Lake County Forest Preserves.
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The moth and the moon

Post by Jen Berlinghof

A full moon rises, a screen door slams shut, a katydid’s creaking calls echo, and a Luna moth (Actias luna) flutters in circles around the back porch light. We’re captivated by this green ghost of summer, concealed by broad leaves and seen rarely during the day, emerging at night only to mate for its few fleeting days of adulthood. How lucky it is that Luna moths live in the Lake County Forest Preserves in northern Illinois.

The bright green wings of the Luna moth (Actias luna) are instantly recognizable. Stock photo.
The bright green wings of the Luna moth (Actias luna) are instantly recognizable. Stock photo.
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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 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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