Author Archive

Why do birds fly south for winter?

by Doug Morin

I opened my backdoor and stepped into the yard to a flash of red and buzz of wings – a hummingbird.  Maybe the last of his kind I will see this year, he perched on a small branch, tilted his head to either side, then flew off down the road.

Here in Vermont, hummingbirds disappear in late September and reappear in late April.  We know the story well: birds fly south for winter.  Of course they do.  But, have you ever wondered why?

First, let’s turn the clock back a few thousand years.  It turns out, most migratory birds in North America trace back to ancestors that lived in the tropics.  Over time, these birds expanded their ranges until a small proportion eventually made it to North America.  Even today, most birds arrive in late spring and leave in early fall – spending less than half their year in North America.  The real question then isn’t, why do birds fly south for winter? but, why do birds fly north for the summer?

This is a particularly important question because migration carries a deep cost.  It’s easy to discount the effort required to fly to and from the tropics, given the convenience of modern air travel (though I’d still like more leg room), but the journey for a bird takes huge amounts of time and energy as well as exposing the bird to unfamiliar environments and predators.  The hummingbird in my yard, for instance, weighed only as much as small handful of paperclips, yet over the next weeks, it will first fly to the southern coast of the U.S., then across the Gulf of Mexico to the Yucatan Peninsula in a single, non-stop flight lasting nearly 24 hours, and finally overland to southern Central America.

The time, energy, and risk involved in migration have severe impacts: migratory birds are twice as likely to die in any given year, compared to tropical non-migratory birds.  So, why in the world do they do it?

The answer is that the benefits outweigh even these high costs.  Since relatively few birds come to North America, migrants have easy access to abundant insects, plants, and nesting grounds.  With plentiful food and territory, migratory birds produce many more offspring each summer than their non-migratory counterparts.  As winter arrives, however, insects and plants disappear, and the diminished food supplies (rather than dropping temperatures per se) drive migrants south.

Overall, migratory birds do not live as long as non-migratory tropical birds, but produce more offspring each year – resulting in nearly the same number of over their lives.  Since the number of offspring determines how many birds will be in the next generation, these two strategies are roughly equivalent in evolutionary success.

So, the birds that grace our summers with color and song do so for windfall payoffs, but at immense cost.  As you see the last of our migratory birds leaving over the next few weeks, wish them well on their way.

Also, look out for a more in-depth post by Emily Brodsky on Raptor Migration in the next few days!

 

Note: For excellent maps of where birds spend their summers and winters, see the Cornell Lab of Ornithology’s website All About Birds.

Chicken of the Woods

by Becky Cushing

Frog legs, rabbit, octopus, sea lamprey: Tastes just like chicken. But a mushroom? That might take some convincing.

Purple toadstools dot moist ground. Tiny aliens emerge from rotting wood. A stalk shoots from leaf litter on the forest floor. Like Alice’s Wonderland, the damp woods in and around Burlington are splattered with wild mushrooms. While identification of the 70,000+ worldly fungi species (many more unnamed) might seem like a daunting task, learning one or two of the “showy” local varieties can be a good way to get started.

Two weeks ago I was exploring Centennial Woods, a natural area managed by the University of Vermont, when I caught a flash of bright orange through the tall white pine and maple tree trunks. Like a reflective safety vest, it stood out against the earthtone browns and greens of the surrounding woods. Squinting harder I could make out suspended shelves attached to one side of the rotting trunk. Getting closer I clearly saw half a dozen two-toned fanned layers, a giant-sized carnation corsage.

Becky with her find.

Becky with her find.

Crouching down I realized this mass was more than a foot wide and each 3-6 inch orange shelf layer was outlined along the waving free edge by a pale yellow, like fresh cow’s milk. Subtle web-like strands of white mycelia penetrated cracks in the dead trunk where, hidden from view, they obtained nutrients through decomposition. If this tree had been alive, it most certainly would have minded this organism’s parasitic affinity for heartwood. As it were, the dead trunk suited the mushroom’s role as a saprophyte, or decomposer.

I recognized this rubbery fungus. I had seen it before. Some call it “sulphur shelf” or “chicken mushroom.” Wikipedia even suggests “quesadilla of the woods” — a bit of a stretch if you ask me. It was Laetiporus sulphureus or “chicken of the woods.”

I’m not a mushroom expert. In fact, I first learned about “chicken of the woods” at an informal dinner party: I thought I was eating chicken. And yes, with loads of butter, it tasted much like the popular poultry. Luckily the skilled chef had several decades of mushroom foraging under his belt but it leads me to an important point: Never ever eat a mushroom without an extremely confident identification (which is usually preceded by many years of foraging experience). For others, past mistakes have caused disintegrated livers or failed kidneys. With 70,000 to 1 odds? It’s just not a good idea.

Subtle Wonders of the High Sierra

by Cathy Bell

After a night spent deeply burrowed into the warmth of my down sleeping bag, I wake to discover that my tent has abruptly transformed itself from a cozy refuge to a swelteringly confined space.  The sun has only just cleared the ridgeline of Cirque Peak, but its rays are strong here at 11,000 feet above sea level, and my little tent heats up like a greenhouse.

Changing from long underwear to field clothes, I clamber out of my tent to find a heavy frost riming the sedges along Siberian Pass Creek.  It is the morning of July 20th.  I don’t have a thermometer, but last night didn’t feel too cold.  I’d guess that the overnight low was in the high 20s.  I stretch and take my time over breakfast, giving the sun a little more time to warm the high country before I set out for my day’s fieldwork.

foxtail forest and Siberian Outpost, Sequoia National Park

Looking over Siberian Outpost.

I’ve set up camp at the edge of a foxtail forest, where widely-spaced pines yield to the treeless gravel flats of the fetchingly-named Siberian Outpost.  Around me, steep talus slopes rear skyward, hinting at the expansive alpine plateaus above.  I am spending my summer in the wilderness of Sequoia National Park, just ten miles south-southwest of Mt. Whitney in the southern Sierra Nevada.  At 14,494 feet, Whitney is the highest peak in the lower 48, but—though it soars a gasping 3,000 feet above treeline—the famed summit is just one of a dozen exceeding 14,000 feet in this region.  Spectacular alpine country abounds: I’ve heard that the Sierra Nevada feature more acres above treeline than any other mountain range in the conterminous 48 states.

The rocky, seemingly-barren high reaches are the reason that I find myself here, in some of the wildest country remaining in the United States.  Though the Sierra peaks seem lifeless from a distance, a closer look reveals a surprising diversity of hardy alpine plants growing amongst the boulders.  I love this hidden world.

tiny Ivesia grows in a rock crevice

Tiny Ivesia grows in a rock crevice.

At the same time, I fear what the future holds.  Research suggests that alpine vegetation is especially at risk from the rapid shifts in temperature and precipitation caused by anthropogenic climate change.  Unfortunately, there are big gaps in our understanding of how high-elevation vegetation will respond to a changing climate.  In fact, since alpine areas are such hard places to access, we don’t even know if their plant communities have already started showing the effects of a warming world.

To try to fill in some of those holes, my master’s project work involves searching for vegetation survey plots that were established some twenty-five years ago.  When I can find the plots, I re-survey them in an effort to compare the plant populations we see today to the ones that were documented in the 1980s, hoping to determine if alpine species are already showing a response to climate change.  So far, the project is going far better than I had dared to hope; I have found every single plot I’ve sought.  Today, I’m going after Plot 403.  I tried to visit it ten days ago, on July 10th, but it was still buried beneath two feet of snow.  I’m hoping I have better luck today.

Shouldering my frame pack with its twenty pounds of field gear, I hike upvalley for half an hour, then scramble up a bouldered slope to the top of a ridge.  As I walk, the rhythm of my footsteps and breath ease me into an almost meditative state.  I take in the dramatic views and reflect on how the wilderness of Sequoia National Park is beautiful but vulnerable.  Though we think of national parks as pristine, even our most highly-protected places are not insulated from human impacts.  The beautiful and diverse plant populations of the High Sierra could be pushed out by changing conditions or the arrival of other plant species, irrevocably altering the character of this unique and inspiring wilderness.  In order to preserve and protect this place for future generations to enjoy, we first have to determine if and how it is changing—and that is what my project is all about.

The ridge brings me west onto the rocky fellfields of the Boreal Plateau, where I start looking for the steel stake that marks the center of Plot 403.  An expansive snowfield still clings to the slope to my right, but it lies east of where the plot should be, and I think I’ll be able to find the plot marker.  I methodically work back and forth, trying to line up the mountains in the distance with rocks on the ground until they match the relocation photo on the clipboard I clutch in my left hand.

dead alpine plant with massive taproot

In life, this plant grew only about an inch above the surface of the ground, but its massive taproot kept it anchored among the rocks.

A brown tangle on the ground catches my eye.  Distracted for a moment from my search, I stop and kneel to peer at the crushed and matted-down plants that the rapidly receding snow has revealed.  Though seemingly dead, most will soon pull energy from their deep taproots and green up, life reasserting itself after the long winter.

Long winters define this world above treeline.   A plant trying to survive here must contend with a growing season of only about two months, howling winds, and an environment that—despite abundant snowfall—is startlingly short on liquid water during the summer, when growing plants require it.  It’s a tough place to make a living, but the alpine plants of the Sierra Nevada are well-adapted to their environment.  They have weathered gradual shifts in climate for a long time.  They are survivors, I know.  I just hope they are able to cope with the climate curveball we have thrown them.

Straightening up, I resume my search for Plot 403, and in just a few minutes I glimpse a flash of reflected sunlight off the center stake.  I take off my pack and get to work.

A Bypassed Giant

by Rachel Garwin

What’s the last amazing thing you overlooked?  I discovered mine last Wednesday in Centennial Woods, a 65-acre natural area near the University of Vermont campus.  A friend and expert naturalist was

white oak sketch

White oak sketch.

sharing his local knowledge with a group of undergrads, and I had tagged along.  The familiar path turned to the left in front of me, but I looked at the woods beyond it as if for the first time.  Gore-Tex dripping with unseasonably chilly rain, I stared unbelieving at the biggest white oak I’ve seen in Vermont.  A white oak I’d never noticed before, despite passing it scores of times in the last year.

Its whitish, ridged bark transfixed me, and I longed for the warmer conditions favored by this southern species.  I heard my friend estimate its age around 300 years, but how could that possibly be?  Too soon we walked away; commitments required our presence back on campus.

For the rest of the week, the white oak filled my thoughts.  My wonder pulled me back to the woods on the crisp, clear Saturday that followed.  I marveled at the oak itself, but also looked at the forest around me with new eyes.  Had I been asked to describe the patch a week before, I would have shared my general impressions of Centennial Woods: a weedy jumble of pioneer trees—red maples, paper birch, white pine—and invasive shrubs that grew up after field abandonment at least sixty years ago.  Now I wasn’t so sure.

White oak acorn caps, © 2011 Rachel Garwin

White oak acorn caps.

Instead of that theoretical assemblage, hardwoods covered the hillside above me. Red maples’ old, platy bark and smooth, young trunks textured the forest, spotted here and there with gargantuan, grooved-barked white pines.  The occasional pines shot straight into the canopy, towering above the broadleaves glinting yellow-green in the sun.  Instead of poison ivy—a scourge on the rest of Centennial Woods—intermediate wood fern and sensitive fern carpeted the duff-covered ground.  Sun flecks danced across fern and leaf alike; their shimmers added another lively layer atop the chatter of insects, blue jays, and red squirrels.

flaky oak bark, © 2011 Rachel Garwin

Up close, the rough, ridged bark is surprisingly flaky.

Cool air washed over me.  I thought of the jacket hanging on the newel post at home, but resisted the impulse to run after it.  Instead, I hopped off the fallen pine and wrapped my arms around the oak, fully two wingspans around.  Rough, flaky bark pressed into my cheek as I looked up along the trunk.

The spreading crown of layered branches dominates the sky.  The branching pattern differs between the lower and upper trunk: until the tree rises above the neighboring red maples and rotting white pines, branches grow only on the southeast side of the oak.  Once free of competing limbs and leaves from other trees, however, the branches radiate in 360 degrees.  Since branches in high light environments have more access to abundant energy, they grow more quickly—and are more likely to survive—than branches in shady environments.  Once the oak’s top emerges from beneath the canopy, however, its branches have equal energy opportunities and reach in any direction.  It follows, then, that this tree grew up on the edge of shady woodland to the west and north, much like the present patch of woods is situated today.

I walked around the massive trunk, careful of roots and uneven ground.  The barbed wire took me by surprise.  Extending from the very center of the tree, the rusted, twisted strands extended east-northeast.  I imagined the wire extending into a fence running further northeast and southwest, through the center of the oak and perpendicular to the growing direction of the lowermost limbs.

barbed wire in white oak, © 2011 Rachel Garwin

Rusty barbed wire protruding from the base of the white oak. The design looked similar to the common Glidden “Winner” variety patented in 1874 and widely available across America.

These waist-thick protrusions of wood would have reached towards the sun-rich pasture across the barbed fence, growing massive.  Today, however, the lowest branches are dead.  When they fall, the trunk will grow around the branch scar, resulting in a large burl.  Lower branch scars exist, but none as striking as what the future holds.  Does this lack of gigantic burls suggest that yesterday’s lower limbs were smaller?  Did the oak originally grow in less sunny conditions on that side, which reduced the amount of energy available to the tree to create huge branches?  Or had the tree simply been younger and smaller, yet unable to produce such girth?  Regardless, the branching pattern suggested that the patchy area to east and south—now growing with young, even-aged, forked white pines—was once open.

My friend claimed the oak was 300 years old, and I’d believe him based solely on the tree’s size.  The oak’s stately bearing is convincing as well.  The spreading canopy still bears a lush complement of waxy, dark green leaves; 300 can be considered middle-aged when oaks have been known to live as long as six centuries.  A relatively fresh acorn cap lay at the ground, however, suggesting the tree is still of reproductive age, or between fifty and 200 years old (though sometimes older).  Without coring the oak, we will never know for certain, and the mystery will continue.   How had I missed it so many times in the past?

fallen oak leaf, © 2011 Rachel Garwin

A freshly fallen white oak leaf lying among bits of old pine needles, maple leaves, and bark chunks on the forest floor.