Thursday, September 13, 2012

Flights of Yellow

Yellow wings flash and click knee-high next to my bike. Up ahead, several sets of yellow wings flap quickly up to the trees. A gentle breeze releases yellow sugar maple leaves from their twigs, and they flutter gracefully to the ground. This sunny gravel road glimmers with the yellows of late summer.

The first yellow wings belong to the Carolina grasshopper. While not especially numerous, they are probably the most common grasshopper you notice. Not only do they prefer roadsides, weedy lots, and the Museum’s outdoor classroom, yellow bands along the edge of black hind wings do a great job of catching our attention.

The grasshoppers’ yellow wing bands flash briefly as they make short flights to escape from predators (or us). When flushed, they fly at a right angle to the predator’s line of travel, then hunker down and use their mottled brown body and front wings to disappear. (This seems like a better strategy than Great Blue Herons, who I have followed for miles down a river in a canoe before they flew out and around us.)

To find food, Carolina grasshoppers make lazy, bobbing flights about 2 feet off the ground, and are often mistaken for butterflies. To find mates, males rise almost vertically from the ground to heights of 3 to 6 feet, occasionally higher, and hover for 8 to 15 seconds. Then they flutter down to the ground near where they started. Late summer is their mating season, and the eggs will hatch next JuneMales, and sometimes females, produce sound in flight. The snapping, crackling, or buzzing sound is made by rubbing the under surface of the forewings against the veins of the hind wings. The short flights attract both females and other males. They remind me of frogs calling each other in to a vernal pool in the spring, or prairie chickens displaying on a dancing ground.

The second group of yellow wings belongs to Yellow-shafted Northern Flickers. As the migrating flock spooks off down the road in front of me, handsome yellow feathers are visible under their wings and tails, and yellow feather shafts show through from above and below. Their white rump patches flash brightly and give another vibrant identification clue.

These woodpeckers spend most of their time feeding on the ground, where their smooth brown back with black bars and dots blends in well with soil and leaf litter. They catch ants and other insects (but not grasshoppers!) with their long, sticky tongues, and dig up anthills to access tasty larvae. Ants are not just food, but also pest control. Flickers rub formic acid from the ants on their feathers during preening to help prevent parasites.

When flushed, flickers make short, undulating flights up to low branches, and often perch like robins instead of clinging to the trunk like most woodpeckers. The courtship flights of the Northern Flicker in spring are noisy and lively, as three or more birds of both sexes perform a comical dance, nodding and bowing or chasing each other through the branches of a tree. Instead of the snapping sound of grasshoppers, the song of the Northern Flicker is a loud wick-wick-wick-wick or a squeaky flick-a, flick-a, often accompanied by a long continuous roll of drumming on spring mornings.

This time of year, flickers head south. (They are one of the only migratory woodpeckers.) Warblers continue on toward Central America in their mixed flocks. Soon harsh frosts will silence the grasshoppers, and maple leaves will have all made their own journey to the forest floor. The wings of fall are bringing beauty and change to our wonderful northern home.

Whose wings have you seen lately?

The Woods are Not Silent

The hermit thrush stopped singing as soon as I wrote about it a few weeks ago. All but a few birds have ceased singing even their late summer songs. While we no longer hear the lilting phrases of love and territorial defense jumbled in a cacophonic morning chorus, the woods are not silent.


Daydreaming on a walk the other day, I gradually became aware of darting movements and soft chip notes in the low and leafy trees. The little flock of foraging warblers engaged in a constant conversation of “companion calls.” These short chips and chirps in a regular back-and-forth rhythm indicate that everything is still okay. In this season, different species of warblers flock together, to make use of many eyes and safety in numbers. They often join with chickadees, who serve as local guides that know the best restaurants and the most dangerous neighborhoods. As they forage for tasty insects and juicy caterpillars, the small birds cannot always keep in visual contact with each other through the leaves. Companion calls help keep track of every bird in the flock.


Finding food right now is important for these little engines that weigh only as much as seven cents. They are on an epic journey. The black-and-white warbler, which I recognized from its striking stripes and nuthatch-like behavior, is heading for somewhere on that species’ unusually extensive winter range – anywhere from Florida to Venezuela and Colombia. Today must be a stopover day, a time to refuel for the journey ahead.


The other warblers in the flock were drab olive green, the standard color of young warblers and adults in non-breeding plumage. Birders know them as “confusing fall warblers.” I could not identify them to species, but it is a safe bet that they also are heading to somewhere in Central or South America for the winter. The secrets of how birds find their way on this incredible journey remain largely hidden. They appear to navigate using a variety of cues that include the stars, the earth's magnetic field, and even smell.


The many-mile migration of these tiny birds is triggered by a combination of factors, including a change in day length, lower temperatures, dwindling food supplies, and genetic predisposition. Since presence or absence of food is not the only or the most important trigger, you can continue feeding the birds through autumn and winter (even hummingbirds!) without fear that your food will interrupt their migration.


Warblers come here in the spring to find a space of their own where they can take advantage of our longer day length and feed ravenous youngsters on our plentiful crop of insects. Their songs are the soundtrack of summer. They leave in the fall when the shorter days and freezing temperatures make those same insects much harder to find. Yet the woods are not silent.


As amazing as it is that these tiny creatures can travel 2,000 miles or more twice a year, I also have a deep respect for the year-round residents who make do and even thrive in the bitter (and beautiful) northern winters. Chickadees, nuthatches, and downy woodpeckers find enough food to fuel their internal fires, and seem almost cheerful throughout the wintry months. Thanks to the wonderful diversity of lifestyles in nature, the woods are never silent!


For over 44 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M. The new exhibit, STAR POWER: Energy from the Sun, opened in May 2012 and will remain open until April, 2013.

Find us on the web at to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

In a Field of Goldenrod, Part II

"Imagine yourself living in a globelike room with greenish walls bulging outward and upward and then arching in to meet above your head," the naturalist Edwin Way Teale wrote. "Imagine such a room constructed of succulent, edible material, forming a house that at once provides food and shelter, plenty and protection. That is what you would find if you traded places with one of those gall insects that now live in the globular swellings on the stem of my hillside goldenrods.

Those galls began their story last spring. After a female goldenrod gall fly, Eurosta solidaginis, deposited an egg on the terminal bud of a growing goldenrod plant, the egg hatched in about ten days. The larva immediately bore down into the stem. The chewing action and the larva’s saliva, which is thought to mimic plant hormones, caused the goldenrod’s stem to thicken.

Soon, runaway cell division triggered by the larva formed a dense, round growth on the stem called a gall. This provided both food and shelter as the larva grew up. After going through three stages, called instars, the larva is ready for winter.

The larva will not leave the gall yet, though.  Instead, it will excavate an exit tunnel in the gall to use in the spring, leaving just the outermost layer as a door. The larva must chew the exit tunnel now, because once it pupates into an adult, it will not have chewing mouthparts. The larva will then retreat to the center of the gall and fill its cells with glycerol, a cryoprotectant that protects cells from damage due to freezing. This is where we are in the story right now.

I often stop to examine the dried, brown galls as I ski or snowshoe through snowy fields. If you open a gall in the middle of winter, you may find the larva, surrounded by the debris excavated from the exit tunnel. They make good fish bait, and are protein-rich snacks for downy woodpeckers and chickadees.

You can tell which bird attacked a gall by the size and neatness of the hole. Downy woodpeckers have a thin, sharp beak that neatly excavates the tough dry material. Chickadees have a blunter beak, and make large messy craters. In contrast, the larva’s own exit hole (if it makes it through the winter) is tiny, perfectly round, with no rough edges, and no concave excavation pit.

Predators help determine the size of the galls. Downy woodpeckers select larger galls to attack, probably hoping for a larger grub. In areas where downies are common, flies with smaller galls survive better, and smaller galls are more common.

Birds are not the only creatures who exploit the gall fly larvae, though. A parasitic wasp, Eurytoma gigantea, uses its long ovipositor to penetrate the gall wall and lay an egg inside. The newborn wasp larva first eats the fly larva, and then continues to feed on the gall tissue until it pupates. The wasp’s ovipositor is only so long, so they prefer to lay eggs in smaller galls. Therefore, in areas where the wasps are common, galls tend to be larger. Where both downies and wasps are common, middle ground is found.

(To see for yourself why goldenrod gall fly larvae appeal to so many predators, I recommend that you taste one for yourself! The concentration of glycerol makes them slightly sweet. I have met many middle school and college students who are willing to accept that challenge! Let me know if you decide to join this Cool Club, too!)

After two weeks as a pupa in the spring, the new adult gall fly will emerge. It will walk up to the goldenrod plant and look for a mate. After mating, the female fly will leave in search of a new goldenrod stem in which to deposit her eggs.

Female gall flies are quite picky about which type of goldenrod to lay their eggs on. Certain fly “races” prefer certain species of goldenrod. The female can tell goldenrod (genus Solidago) species apart by “tasting” the plant with chemical sensors on their feet, antennae, and even in her ovipositor! When the right plant is found, a few eggs are laid, and the story beings again.

Once predators, parasites, or metamorphosis empties the galls, they become habitat for a variety of insects.  Springtails, wasps, solitary bees, beetles, and ant colonies have been discovered using the galls. Next time you go for a walk or a ski in a field of goldenrod, take a moment to imagine yourself spending the winter in the globelike room of a goldenrod gall.