Friday, November 20, 2015

Camp Robbers and Broken Refrigerators

The thick carpet of pine needles felt springy and dry under the trees. Patches of sunlight kindled warm fragrances to tickle our noses. On the wooden wildlife observation deck, though, an inch or so of soggy snow—not fit for November—dripped steadily through the planks. Skims of ice only clung to the shallowest pools in the marsh, and in one bay, a column of mist rose from the dark water. Although it was just past noon, the low angle of the sun illuminated the swirling cloud in soft light as it danced in partnership with the breeze.

Abruptly, a raucous “kreh kreh kreh” erupted from the edge of the pines. My first thought was a merlin – a small falcon with a big voice. But merlins head south in September, and the peak of their migration is long past. I peered into the pine boughs where the sound originated, and caught a glimpse of a gray-colored bird a little bigger than a robin. As soon as I spotted it, the bird flew. Our visitor didn’t high-tail it into the bushes, though, it made an unhurried swoop toward us on downward angled wings, and perched in a nearby birch. There was no mistaking that flight pattern; the alarmist was a gray jay.

The habitat range of these non-migratory birds--once called Canada jays—encompasses most of Canada up to tree line, and scoots just under the nose of Lake Superior like a mustache. Here at the southern edge of their range they aren’t very common. Usually I have my annual encounter with a “camp robber” in the Boundary Waters or Sax-Zim Bog north of Duluth.

Why do they live so far north? Gray jays seem to be dependent on two things: a strong presence of certain tree species (black and white spruce and jack pine in our area), and cold temperatures. Both requirements relate to their food storage method.

In order to survive the long, bitterly cold winters in their range, gray jays must put up food all summer and fall. They accomplish this by coating mouthfuls of food in sticky saliva, then gluing the boluses in tree crevices, under lichens, in evergreen needles, and behind the flaky bark of their preferred tree species. A gray jay may hide 1,000 separate caches of food in a single, 17-hour day. “Scatter-hoarding” is the technical term for this technique. “Gray jays have a memory like a Vegas card counter,” writes Joe Rankin in Northern Woodlands magazine, referring to the fact that the jays seem to be able to retrieve 80 percent of their food-filled saliva balls. 

At least a portion of the lost 20 percent is due to spoilage. Some boreal tree species may contribute antibacterial compounds that help the food stored under their bark stay fresh. But that’s not enough. Cold temperatures in the gray jay’s preferred habitats are necessary to prevent cached food, even chunks of meat, from spoiling.

On this lovely, sunny, warm day in November, the vulnerability of these southernmost gray jays was driven home. Their refrigerator is broken. This is the warmest fall on record, and that doesn’t bode well for the longevity of cached meat and other food. Their reproductive rates may suffer, since gray jays nest in late winter, and feed nestlings from their caches. A study by the University of Guelph in Ontario confirmed that gray jays are food-limited during the breeding season. The researchers connected this with warmer fall temperatures allowing food to spoil and a 50% decline in numbers of gray jays in Algonquin Provincial Park over the past three decades.

It’s not because they’re picky eaters, either. Gray jays are opportunistic omnivores, and they consume everything from small mammals, nestling birds, carrion, and arthropods to fungi, fruits, and seeds. They have been observed picking engorged winter ticks off the backs of moose. Anyone who has camped within their range knows that these “camp robbers” are not shy about snatching up a crust of bread off the picnic table, or nabbing a marshmallow before it can become a s’more.

Our lack of food made us boring to the “camp robber” who came to investigate. He scrutinized us for only a minute before flying off. Since gray jays mate for life and stick together year-round, I would guess that this solo guy is a bachelor, and probably a young of the year. Even without the broken refrigerator, his is a tough lot.

In early June, the two-month-old chicks begin an intense sibling rivalry. Only one dominant juvenile gets to stay with its parents, after driving the rest of the young away. These “stayers” gets access to their parents’ food caches and mentorship, in exchange for helping to raise little brothers and sisters the next summer. Even with the help, they still face a 52 percent mortality rate. The “leavers” that get kicked out may be able to volunteer their nanny services to an unrelated pair currently without chicks of their own. Or they may simply perish during the hungry winter. Leavers experience an astounding 85 percent mortality rate, while stayers only die about half the time.

As we gazed over the wetlands and pine forests, the midday sun warmed my face and the unseasonable weather made me sigh. That lonely jay had every right to scold us for breaking his refrigerator.

[Columnist Emily Stone is publishing a book of her Natural Connections articles as a fundraiser for youth programming at the Cable Natural History Museum. Since kids are often the inspiration for her articles, the Museum is conducting an art contest for local students to illustrate each of the 52+ chapters. The hope is that students will read some chapters, learn something about the plants and animals in those chapters, do a little more research on their own, and then create a black-and-white line drawing based on their research. The best and most relevant illustration for each chapter will be included in the book. Please share this opportunity with any kids in your life! Entry forms can be found]

Gray jays are charismatic camp robbers that live close to their southern limits in Northern Wisconsin. Photo by Skip Perkins.

Friday, November 13, 2015

I Like Lycopodium

The gleaming white magic of a winter wonderland enticed me outside after breakfast. With our first snow on the ground, the air tasted fresher, the brisk cold nipped my cheeks awake, and the world felt new.

Above me stretched a lacework of light and shadow against the widening blue. All around me, the thin layer of sticky snow created lush patterns on the forest floor. Pebbles in the driveway, twigs on the ground, and ferns leaning over became works of modern art under their crust of white. Christmas tree-sized balsam firs hugged their snow-laden branches close.  In the understory, mini trees did the same.

Only those mini trees aren’t really trees, at least not anymore. You might know them as ground pine, prince’s pine, or club moss. If you’re botanical, you might even know them by their genus Lycopodium (Greek for little wolf foot). None of those names are entirely accurate, though. These definitely aren’t pines, or mosses (or wolves!), and new DNA studies have made the scientific classification more complicated, too.

Lycopodiums are beautiful and amazing, though, and harken back to the Carboniferous Period more than 300 million years ago. At that time, North America was part of the supercontinent Pangea, and the eastern United States was positioned near the equator. Beautiful plants, gigantic insects, and strange forests covered the land. Increased precipitation, carbon dioxide, and oxygen created a very different world than we know today.

The tropical climate produced extensive swamps dominated by the ancestors of our little lycopodiums. Tree-like or “arborescent” lycopods were some of the first plants to grow secondary tissue (wood), which was needed to support their impressive heights of 50 meters (164 feet). That is taller than the tallest white pines currently growing in Minnesota or Wisconsin.

What’s crazy is that they couldn’t increase their girth along with their height. Each tree had to begin its life by growing its trunk as wide as it would ever be. The thick stump grew upward into a pole of the same diameter. Leaves – also known as microphylls because they only have a single vein down the center – grew along the trunk. With only the single vein, though, they had no way to transport the sugars produced by photosynthesis. As the tree gained height, the lower leaves fell off (creating a distinctive pattern on the trunk), and the lower trunk essentially became dead tissue. At some predetermined height, the tree branched a certain number of times, reproduced, and died.

With such a “quick and cheap” lifestyle, the lycopodium ancestors both grew and died rapidly. This allowed them to dominate habitats following short-term disturbances (like frequent fires), and leave behind a tremendous amount of woody debris in those tropical swamps. If you tried to imagine such a swamp today, you’d probably envision a mucky forest full of rotting logs. Back then, however, fungi hadn’t yet developed a good way to decompose wood – especially the tough, brown lignin in wood, and charcoal – so tree trunks would have lain around for years.

Charcoal? In a soggy swamp? There is evidence that the high oxygen levels in the Carboniferous Period atmosphere allowed large-scale firestorms to sweep across the globe. The charcoal and other organic matter left in the swamps was eventually buried and turned into coal.

The unique conditions present during the Carboniferous Period may never be repeated on earth. As carbon in the air became locked up in coal deposits, in the explosion of land plants, and in limestone beds under the ocean, the conditions no longer supported giant lycopods. They shrank into the diminutive “prince’s pine” we know today. Complex plants with seeds, extensive vascular systems, and trunks that could grow out as well as up succeeded instead.

The branches of this new forest closed in over my head, as I appreciated the beauty of our current non-tropical weather. Tiny snow-capped lycopods dotted the understory landscape—their diminutive size hiding an immense history and adding to the magic of the forest. In nature, things are surprisingly old and always new.

Lycopodiums (also known as club moss), dominated tropical forests 300 million years ago. Today, they are tiny, understory plants beneath a new era of trees. Photo by Emily Stone.

Friday, November 6, 2015

The Leopold Shack

Happy to exit the car after a long drive, I inhaled a sweet lungful of damp leaf perfume. A giant oak towered above the trailhead as we sauntered into the forest – eagerly, but also thoughtfully. We continued through a tall, damp meadow full of weed seeds and a mist so fine it swirled rather then fell. The brown, wooden shack with a white painted door stood in a small clearing. Although quite humble in appearance, there was a certain dignity about it, as well as an aura of wisdom.

“Every farm woodland, in addition to yielding lumber, fuel, and posts, should provide its owner a liberal education. This crop of wisdom never fails, but it is not always harvested.”

This shack was the weekend escape for a University of Wisconsin-Madison professor named Aldo Leopold and his family. On a worn-out, abandoned farm in the “sand counties,” Leopold set out to see if he could return health to the abused land. He also harvested--many times over--its crop of wisdom.

The liberal education provided by Leopold’s farm resulted in his writing of “A Sand County Almanac,” and the idea of a “land ethic.”  I still remember the first time I read and underlined one of his most powerful quotes: “A thing is right when it tends to preserve the integrity, stability and beauty of the biotic community. It is wrong when it tends otherwise.”

I love that Leopold includes beauty as a value of nature. As we stood in front of the Shack, chatting with an educator from the Leopold Foundation, she waved her hand toward the elegant silhouettes of mature pines. “The Leopold family planted thousands of pines every spring,” she said. This forest is their legacy, their work of art.

“To plant a pine, for example, one need be neither god nor poet; one need only own a shovel. By virtue of this curious loophole in the rules, any clodhopper may say: Let there be a tree-and there will be one. If his back be strong and his shovel sharp, there may eventually be ten thousand.”

While Leopold may understate his role as an artist, the loveliness of his land boasts for him.
“Some paintings become famous because, being durable, they are viewed by successive generations, in each of which are likely to be found a few appreciative eyes.” By the popularity and success of the Leopold Foundation’s program and message, it is clear that this shack, its farm, and their message is finding many appreciative eyes in successive generations.

On this damp, fall afternoon, two generations of conservationists explored Leopold’s legacy together. My parents were born just before “A Sand County Almanac” was published in 1949. In the 1990s, my dad traveled with a box of those books; always ready to give one away with the recommendation “I think you should read this.”

Chickadees chattered from the boughs. The leaves of sharp-lobed hepatic glistened in the understory. Lilacs, geese, “red lanterns,” of blackberries, birch, and the winding Wisconsin River – the characters from Leopold’s writing – all surrounded us on our walk through the autumn pines.

“All [pines] write the same thing, in the same tawny yellow ink, which by November turns brown. Then the needles fall, and are filed in the duff to enrich the wisdom of the stand. It is this accumulated wisdom that hushes the footsteps of whoever walks under pines.”

Walking quietly, we reflected on the accumulated wisdom of this special place. Wisdom from the past that is needed for our future.

The Leopold Shack, Photo by Emily Stone

Friday, October 30, 2015

Carolina (Chickadee) On My Mind

Engines roared as the plane prepared for liftoff. The force pressed me into my seat – upright and with tray table stowed – as we separated from the ground. I peered eagerly through the double-paned windows at the bird’s-eye-view. The grid of Duluth and white-capped Lake Superior (surf’s up!) zoomed by. Damp and brown, with rounded edges, the lakes, forests, and swamps of northern Wisconsin appeared next. Ringing each circular bog (each created by a chunk of glacier that was buried and melted) was a border of bright yellow. The tamaracks were in full fall color.

On the other end of my journey, forested riverways squiggled among a crazy quilt of farm fields outside Raleigh, North Carolina, as we prepared for landing. Green trees seemed oblivious to the imminent onslaught of winter. Descending into a week of sunny-and-75 felt like a trip back to August, and was disorienting. While attending a conference gave me some structure, I still had to navigate this unfamiliar city landscape to find food among the highways and stoplights. Thinking back to all the birds I’d recently watched head south over Hawk Ridge in Duluth, I felt a deeper sense of empathy for the challenges they face on migration.

Happily, on my last afternoon, a friend whisked me away to the beautiful Sarah P. Duke Gardens on the Duke University Campus. Somewhere past Azalea Court and the Dawn Redwood, a birdcall stopped me in my tracks. It was just a simple dee-dee-dee from within a small tree, but it sounded so familiar. Peering through the thick foliage, I glimpsed the black-and-white face of a little chickadee. Instantly, I felt more at home. Black-capped chickadees gurgle at each other over seeds outside my window each morning, and some form of chickadee has always accompanied me on my travels. This Carolina chickadee felt like the local welcoming committee. (Never mind that it was scolding me for being in its territory).

I’m not alone. Across the country, migrating warblers in unfamiliar territory seek out flocks of residential chickadees as local guides. The chickadees pass on information about the best food sources, and are tuned to local threats. Chickadees are such helpful hosts that throughout the winter, many species of birds associate with their black-and-white flocks.

The small winter flocks of both types of chickadees consist of a few mated pairs, and the recent offspring of pairs from other flocks. Young chickadees don’t hang out with their parents; this prevents inbreeding. Each flock has a strict dominance hierarchy for each sex. Watch the birds at your feeders closely – subordinate birds quickly put down their seed and leave if a dominant bird gurgles at them. Despite their gregarious daytime personalities, each chickadee sleeps in its own shelter or cavity.

Besides having slightly different calls, black-capped chickadees are also adapted to colder, harsher winters. The division between the two species seems to be the band of average minimum winter temperature of 17 degrees Fahrenheit. This line – and the boundary between the two species – stretches from New York City to Kansas, with a steep dip south along the Appalachian Mountains in West Virginia and Tennessee. In a 20 mile wide band along the divide, the chickadees hybridize.

Several fascinating research projects have given us a glimpse into this band of illicit romance. Turns out, when females of either species don’t know which male is dominant, they sidle up to the black-capped chap. But when the males interact, Carolinas usually dominate, and females of both species dig that. The resulting hybrids are almost impossible to recognize physically, but their songs are a confusing mashup of both species.

Another incredible discovery is that this band of hybridization has been moving steadily north – nearly a mile a year in some areas – and it follows the trend of rising temperatures. This shift has been occurring for at least half a century, and probably since the retreat of the glaciers that formed our tamarack-ringed bogs.

While northern Wisconsin will remain a stronghold of black-capped territory for many years (our current average minimum winter temperature is 10 degrees Fahrenheit), cities like Chicago, Springfield, and Kansas City may soon be dancing to a different tune. Happily, the warblers and I can still count on chickadees to help us feel at home wherever we go.
Carolina Chickadee Photo by Dan Pancamo

Friday, October 23, 2015


Heavy gray clouds settled in for the afternoon, giving off the aura of November. During my drive home from work, though, a break had opened to the west, and focused beams of gold snuck under the clouds. The last, clinging, yellow leaves of aspen and maple, and the rich red-browns of the oaks, lit up like they were on fire. A stiff breeze whisked their fallen comrades into whirlwinds of color. Leaves stirred up from the ground met leaves just now fleeing the leaden sky.

From that whirling chaos of leaves and light and wind also emerged swirling flocks of small, gray birds, with white belly and tail feathers flashing. Snowbirds, some folks call them, because their plumage imitates the winter color scheme of dark skies above and white snow below. Here, in their overwintering habitat of the lower 48, they also seem to bring the snow with them as they move south each fall.

Dark-eyed juncos breed across Canada, with some subspecies staying year-round in the Appalachian Mountains, the West, and the Northeast. The northern forests of Wisconsin and Minnesota are at the southern edge of their mid-continent breeding habitat, and we sometimes see a few juncos through the summer. You can identify them by the flash of white on their outer tail feathers as they fly away. The real influx comes when the leaves begin to fall, as juncos head south to their winter range.

This year at Hawk Ridge Bird Observatory in Duluth, MN, their migration began on September 10, with a single junco, and peaked in early October with counts of 1593 on October 7, and 1224 on October 13. While I don’t count the dancing flocks that rise from the roadsides and fields, I, too, have noticed the wave of junco migration.

Females tend to migrate the farthest south, and comprise 70% of winter flocks in the southern United States. Males will risk harsher weather farther north in order to get a jump start on spring migration and arrive first at prime breeding territories.

Their impressive and easily observed movements have taught us much about migration in general. Prior to 1924, the best hypotheses about how birds know when to migrate and breed centered on them responding to changes in temperature and barometric pressure.

William Rowan, who founded the Department of Zoology at the University of Alberta, suspected that day length was more important. Without the support of the University president, Rowan conducted an experiment to confirm his theory – in secret. With two outdoor aviaries full of juncos – one with lights and one without – Rowan spent a very cold winter in Alberta simulating the increasing daylight of spring.

After three months of increasing “day length” by five minutes per day, Rowan’s juncos began to sing. It seems obvious now, as I gather eggs by a lamp’s artificial sunlight in the chicken coop, but Rowan’s experimental confirmation of “photoperiodism” was a major advance for science.

Being easily caught, able to thrive in captivity, and adaptable to new habitats, juncos make excellent experimental subjects. Rowan’s was just the first of many junco-based experiments. Currently, scientists are comparing the various subspecies of juncos that live across North America to study evolution and speciation. One population of juncos on the campus of UC-San Diego seems to have evolved new behavioral and physical traits in just 30 years.

Juncos make wonderful winter friends for citizen scientists, too. The Cornell Lab of Ornithology’s Project Feeder Watch notes that “juncos are sighted at more feeding areas across North America than any other bird. Over 80% of those responding report juncos at their feeders.”

This abundance is likely due to the fact that juncos are primarily seed-eaters who forage in flocks. Under the feeders, along roadsides, and in open areas, juncos will forage by hopping, scratching, and pecking at the leaf litter, and flying up to glean food from low twigs and grasses. These sparrow-sized birds will even land on the top of a grass stem and use their 25 gram bodyweight  (the equivalent of 25 paperclips) to “ride” it to the ground. From there, they can stand on the seed head and feed more easily.

According to Don and Lillian Stokes of the Stokes Field Guide to Birds, watching the social hierarchy at work in a junco flock can be quite entertaining. The same birds tend to return each year, and the earlier arrivals tend to rank higher in the flock. When asserting dominance, a junco will face the offending subordinate bird and fan his tail to reveal the white outer tail feathers. Sometimes a chase, dance or, pecking fight will ensue.

Juncos were already scratching under my feeder when I stepped outside the next morning. The gray skies had lifted, but in their place was a light dusting of white flakes on the car. The snowbirds are back.

Friday, October 16, 2015

How to Make a Beaver Sparkle

Cool water swirled around my rubber boots as I waded out into the dark, star-studded lake. A sense of peace began seeping in with the chill. Then, SPLASH! From out of the darkness came the unmistakable sound of a beaver slapping its tail in alarm. Of course I looked up, and my light caught his swimming form in the beam.

I chuckled at my own surprise. Then immediately I began thinking of how I would tell this story to the kindergarteners during my MuseumMobile program the next morning as we passed around the dried beaver tail.

Beavers are not my favorite animal. Their drab, oily fur, plodding manner, and lumpy design don’t inspire the same feelings of wonder in my heart as a cheery little chickadee, rangy wolf, or glittering dragonfly. But over the years, I’ve come to enjoy teaching about them nonetheless.

During an internship at Acadia National Park, we included beavers in a fourth grade field trip called “Animals of Acadia.” The big, yellow buses started at The Precipice – the nesting habitat of peregrine falcons. On a good day, we could see their elegant forms darting gracefully in front of a craggy cliff. It took me a while to understand how peregrines and beavers fit into the same program – the only time beavers look elegant is after they’ve been skinned and felted into hat – but I came to appreciate their parallel histories of exploitation and steep decline, as well as protection and recovery.

One of the goals of the Acadia field trip was to teach the students about animal adaptations. While you can hardly find two animals that are more different, beavers and peregrines also share the reputation of being extremely well adapted to their particular lifestyles.

As the beam from my headlamp followed the beaver on his journey, his eye sparkled back at me just above the surface of the silver lake. I paused to admire the effectiveness of his oddly-shaped head. Just that morning I had pulled a skull out of the education tub to show some second graders how the beaver’s eyes, ears, and nose are all crowded toward the top of his head. This allows the beaver to hear danger, see where he’s going, and breathe continuously, even while having most of his head and body stealthily submerged.

I also enjoyed watching the kids react to the news that beavers have a third, translucent, eyelid that closes sideways and acts like swim goggles. They were jealous! I could see their little minds churn as they imagined what they could do in their favorite lake with built-in goggles. I wouldn’t mind having the beaver’s ear, nose, and throat flaps to keep water out, too.

The beaver’s rust-colored teeth also caught the students’ attention and spurred questions – which is one reason I love having access to dead animal parts for teaching. The orange surface isn’t due to poor dental hygiene. (Although, maybe saying that would encourage kids to brush their teeth more.) The orange color comes from iron in the enamel which strengthens the surface and buffers the teeth against acid that could cause tooth decay. The iron works even better than fluoride!

Behind the orange surface, the beaver’s front teeth are made of softer, white dentin. As the beaver gnaws down trees, the dentin wears away at an angle behind the enamel, resulting in self-sharpening points – an innovation that would be welcome in my knife drawer!

When I teach kindergarteners about beavers, we don’t go into those details. We stick to the theme of “exploring nature with our senses,” which means taking turns touching a beaver pelt. They get to experience the soft, dense underfur that provides insulation, and the long, glossy guard hairs that help keep the beaver waterproof. At one of my favorite schools, a little class clown sprawled out on the fur, then grabbed a corner and rolled around like the beaver hide was attacking him. His classmates ignored what must have been a familiar scene, but I had to work hard not to laugh.

The kids also pass around a cloth bag concealing a beaver tail. Flip-flop, shoe, and flyswatter are some of their guesses about the mystery object. About once a year, one outdoorsy kid will recognize the tail right away. Inevitably, the kids are curious, and want to touch the tail again. When I ask them how the beaver uses its tail, inevitably I have to clarify that only cartoon beavers use their tails to pat mud on their lodge. Real beavers use their tails to swim, store fat for the winter, as a kick-stand while cutting trees, and of course, for slapping the water in alarm.

Before I even finished the story of my nocturnal beaver encounter, six little hands shot in the air, eager to share their beaver encounters, too. The kids’ enthusiasm was a bit like my flashlight – adding a bit of a sparkle to an otherwise dowdy creature. 

Friday, October 9, 2015

Thistles and Those Who Love Them

Ouch! I cursed as something in the handful of weeds pierced my hand. With the coming of the frost, it was time to clean out my garden. In this corner, a small patch of parsley had gotten overgrown by the gracefully arching seed heads of a grass. My flesh had found the spiny, well-armed basal leaves of a thistle in the bunch, too. The deep green leaves spread out in a perfect circle, at least a foot in diameter. Spines adorned the jagged leaf margins menacingly. This year it didn’t produce a flower stalk. Next year it won’t either—because with a quick pry of the pitchfork I dislodged the offensive weed, roots and all.

As I continued to load up the wheelbarrow for a trip to the compost pile, I waded into the overgrown garden border to remove a couple of bushy, second-year thistle plants, too. (I donned gloves for this task.) A closer look revealed spiny wings of leaf material along the stems – a sure sign of a non-native thistle, probably bull thistle. Although many of the seeds had already drifted into my green beans, I figured I could keep at least a few more seeds out of the garden.

Each summer I struggle with time management – as soon as I start harvesting, I stop weeding! If I was really responsible (a.k.a. not busy), I’d have taken care of all the late summer weeds before they went to seed. But, when life gets busy and I have to choose, I pick beans.

In some ways, I’m also choosing to share my garden with wildlife. As long as thistles don’t take over an area from native plants or interfere with grazing, they can benefit a surprising number of species. At least twenty-three species of insects feed on thistle foliage. Countless other insects (and hummingbirds) feed on the nectar and pollen. Even more spiders, birds, reptiles, amphibians and mammals eat the critters that feed on the thistles.

Of course, native thistles will host the most diversity of life. Most need high quality prairie remnants to thrive. Bull thistle may not be ideal, but at least it is a biennial and dies after producing seed in its second year. It can be a problem in disturbed areas, but generally won’t take over quality habitat. Canada thistle (actually from Europe) forms perennial colonies that are much tougher to eradicate.

I suppose one reason I didn’t bother to pull the thistles earlier in the summer – when they still sported fuzzy, fuchsia flower heads – has to do with some childhood nostalgia. As a native Iowan, I have a special place in my heart for goldfinches (they are our state bird). For as long as I can remember, I’ve been taught that goldfinches have a special relationship with thistles; first by my parents, and then by poet Mary Oliver:

“the finches/wait for midsummer,/for the long days,/for the brass heat,/
for the seeds to begin to form in the hardening thistles…”
 – from “Goldfinches” in New and Selected Poems by Mary Oliver.

I first learned that American goldfinches nest later in the summer from this very poem. While the little yellow birds use the soft fibers of thistledown to line their nests, in truth, it is the energy-packed thistle seeds they are waiting for.

If you feed birds, you know how much goldfinches love thistle seeds. The seeds in your feeder aren’t even true thistles. They are seeds from the unrelated African nijer thistle. In the wild, many relatives of thistles in the Aster or Composite family are favored food sources for goldfinches, and most of them are late-summer bloomers. Thistle is one of the most common, as well as Joe-Pye weed, and sunflowers. Dandelions are an early-blooming exception, and goldfinches may feed heavily on spring dandelion seeds in addition to the seeds you put out.

As seed-eating specialists, finches are among the most strictly vegetarian birds of the world. While many small birds eat seeds, most of them also feed insects to their young. Finches feed their chicks exclusively on regurgitated seeds! This has an unexpected advantage: when brown-headed cowbirds try to mooch (they are nest parasites who don’t build their own nests, and instead lay their eggs in the nests of other birds), the invading young die after three days on this diet.

With such a strong reliance on thistles for their nesting success, goldfinches need to make sure that their timing is perfect. One researcher found that male goldfinches exposed to both warm temperatures (a July-like 82 degrees F) and blooming thistles will rev up their testosterone production. It is pretty incredible that they respond to the flowers as a precursor to seed production, and not just the seeds themselves.

As year-round residents, goldfinches don’t need to hurry up and prepare for migrating thousands of miles. Instead, they can patiently make use of an abundant late-summer food source. As I hauled the loaded wheelbarrow toward the compost pile – a crown of thorny thistles perched on top – a flock of goldfinches sang me cheerfully along. 

A goldfinch gathers thistledown for its nest. Photo by Larry Stone