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By Sonia DeYoung
Outside my window, a robin pecks around in the rain. It’s the day before Thanksgiving, and the forecast calls for the rain to turn to snow tonight in my Massachusetts hometown. So why isn’t this robin right now flying south toward a warm, easy winter?
Casual birdwatchers see robins as harbingers of spring, but you can actually find them year-round throughout much of the U.S. Based on my own observations, robins seem to stick around more now than they did twenty years ago—perhaps global warming plays a role in that trend (see November 6 post). But climate change can’t explain why some robins flee wintertime and others take their chances.
[Update: The day after publishing this post, I stumbled across an article by biologist Mark Davis saying that more robins stay in the north for the winter now because of a greater winter food supply: they happily eat the berries of several increasingly common non-native species.]
Many birds, like warblers and hummingbirds, migrate annually no matter what. Others, including robins, kingfishers, and chickadees, are “partial migrants”: within a single population in a given year, some will migrate and some will not. Backyard birdwatchers who rejoice in the first robin of spring aren’t necessarily unobservant. There are fewer robins around in winter, and those that do stay often roost in bogs and swamps instead of backyards. Each year, a robin must decide based on the available food supply whether to migrate; a snowy winter landscape can never provide as much food as the same land in summer. Some robins may even leave mid-season if the conditions turns especially harsh.
They’re taking a gamble either way. Birds who reside year-round in temperate climates risk a 50-80% chance of death each winter. Migrants do a little better, with at most a 50% chance of death. But they invest a great deal of time and energy in migration that they could have put toward reproduction. Temperate residents make up for their high winter death toll with their better success raising offspring.
Not all partial migrants have to make this annual choice. Within a single population of European robins (not closely related to American robins), genes dictate which individuals will migrate and which will stay. With these birds, migrants are born, not made. Gene-determined migrants like European robins are called obligate partial migrants, while American robins are examples of facultative partial migrants.
Still other kinds of migrants do make a choice, but it’s a group decision. Evening grosbeaks and snowy owls, for instance, will leave their typical wintering grounds en masse if the autumn produced a poor seed crop. Then they pop up in unexpected places in what’s called an irruption: an unpredictable winter boom of birds.
The robin outside my window, though, didn’t have the advantage of consensus to decide where to spend this winter. She reminds me that animals are individuals who must make daily life decisions based on their experiences. Watching her hunched under the cover of a dripping rhododendron, I hope she made the right one.
Information gathered from The Handbook to Bird Biology published by the Cornell Lab of Ornithology; Living on the Wind: Across the Hemisphere with Migratory Birds by Scott Weidensaul; and the Audubon Society and Smithsonian field guides to North American birds.
Snorkeling in frigid waters for a species at-risk
By Levi Old
“We have a large adult!” says Jen.
I rise to one knee and pull the fogged snorkel mask off my head. “A big one?” I mumble in a haze.
“Yeah, really big. Much larger than I’ve ever seen this far up the creek,” she replies, pointing to where it kicked its caudal fin gently against the downstream flow. “It’s right there beside you.”
I cinch the mask on my face, place the snorkel in my mouth, and dunk back into the frigid water:
Twenty-six inches of wildness.
Jen pops her head out of the water and says, “Isn’t that just a beautiful creature?”
She snorkels one side of the creek and I snorkel the other. An assistant in waders walks the creek, tallies our fish sightings and makes sure we do not go hypothermic.
Jen O’Reilly, a biologist for the US Fish and Wildlife Service, leads the recovery effort for the Odell Lake population of bull trout, a Threatened Species under the Endangered Species Act. The recovery team consists of US Forest Service, Oregon Department of Fish and Wildlife, and Trout Unlimited. In order to monitor recovery of bull trout, biologists conduct an annual juvenile count in Trapper Creek, the only known spawning location for this population.
Trapper Creek is a tributary to Odell Lake. In the shadow of Oregon’s Diamond Peak, the lake lies in a glacier-carved basin physically detached from the Deschutes River by a 5,500 year-old lava flow. The flow enclosed the lake, genetically isolating this population of bull trout.
At midnight this past July, ten of us in dry suits and thick neoprene hoodies shimmied up different reaches (Fig. 1) of Trapper Creek. Shallow in most places, the snorkel is more of a crawl and scramble than a leisurely swim upstream. Even in mid-summer Trapper Creek is icy cold.
We closely observed the nooks of each piece of in-stream wood and dove into pools where rapids converged and bubbles enveloped our sightlines. We held dive lights, counted each fish and estimated its size class. We kept our eyes peeled for the creek’s bull trout.
Bull Trout – A species at-risk from Levi Old on Vimeo.
Named for their broad heads, bull trout (Salvelinus confluentus) serve as apex predators in aquatic systems of the West. Often called “Dolly Varden (S. malma),” they are in fact a separate species. Bull trout exist in less than half their historic range and prefer clean, cold waters. As a member of the char genus, they grow to be shark-like beasts in comparison to their trout relatives. Bull trout can measure up to 41 inches and weigh as much as 42 pounds.
The Trapper Creek bull trout population is known as the only adfluvial, non-reservoir population of bull trout in Oregon. During the 20th century, the building of railroads, construction of revetments, and removal of woody debris turned the creek into a large ditch of rushing water, unsuitable for spawning bull trout.
In 2003, this all changed. The recovery team restored the channel to increase spawning and rearing habitat by deconstructing revetments, placing woody debris and rebuilding a meandering channel. The annual snorkel count of juvenile bull trout increased from 26 in 1996 to 150 in 2005. Restoring, sustaining and monitoring native habitat is crucial to the survival of this iconic species.
If you find yourself on western waters, keep an eye out for these stream predators. Light spots of yellow, red and orange cover their dark bodies, and a white margin can be found on the leading edge of their ventral fins. And watch out, anglers: they will steal a hooked fish right off of your line.
Enjoy the video:
Bull Trout – A species at-risk from Levi Old on Vimeo.
- Montana Water Center. (2009). Trapper Creek. Retrieved on October 16, 2014, from http://wildfish.montana.edu/Cases/browse_details.asp?ProjectID=36.
- Richardson, Shannon and Jacobs, Steve. (2010). Progress Reports. Retrieved on October 16, 2014, from http://oregonstate.edu/dept/ODFW/NativeFish/pdf_files/Odell_BT_Report_final.pdf.
By Bryan Pfeiffer
On a crisp, sunny day in September, after what was probably a typical summer for a dragonfly (which involves flying around, killing things and having sex beside a pond), a Common Green Darner took off and began to migrate south. As it cruised past the summit of Vermont’s Mt. Philo, with Lake Champlain below and the Adirondacks off in the distance, the dragonfly crossed paths with a Merlin.
The Merlin, a falcon that kills in flight, swerved, plucked the dragonfly from the sky with its talons and began to eat on the wing. As the falcon and its prey continued southbound, all that remained in their wake was a single detached dragonfly wing, falling like an autumn leaf toward fields at the base of Mt. Philo.
Eagles, hawks, falcons and Monarch butterflies aren’t the only migrants moving south past mountains this fall. Joining them are dragonflies. Although biologists know plenty about the fall raptor and Monarch migrations, we are only beginning to discover, with some creative chemistry, where these dragonflies go and how migration figures in their conservation.
Fly or Die
Most dragonfly species do not migrate. In fact, most are now dead, having already mated during the summer season, leaving behind eggs or larvae to survive the winter. The killing frost will finish off much of what’s still on the wing. But some survivors will leave.
Among the 460 or so dragonfly and damselfly species native to North America, at least five are classic migrants: Common Green Darner (Anax junius), Black Saddlebags (Tramea lacerata), Wandering Glider (Pantala flavescens), Spot-winged Glider (Pantala hymenaea) and Variegated Meadowhawk (Sympetrum corruptum). Each species is on the move this fall.
Dragonflies migrate for the same reasons other animals migrate: to avoid inhospitable conditions, in this case habitats that freeze or become too cold for the dragonflies themselves or their insect prey. Monarchs go to Mexico. Broad-winged Hawks leave for wintering grounds stretching from southern Mexico into South America. Dragonflies head south to who knows where.
Having studied birds for two centuries, biologists know well their breeding and wintering distributions , even to the point of learning the destination of a particular warbler or sparrow after it leaves us in the fall. Ornithologists catch lots of songbirds in nets and place around one leg a tiny silver bracelet embossed with a unique number – an avian social security number – and then release the birds to the winds. A small percentage of them, still sporting their bracelets, are later recaptured while in migration or on wintering grounds thousands of miles away. Better yet, we’re putting small electronic transmitters on large birds, such as Bar-tailed Godwits and American Woodcocks, and tracking their movements real-time with satellites.
We can even track the movement of a single butterfly. I myself have placed little stickers, each bearing a unique alpha-numerical code, on the hind wings of more than 1,000 Monarchs here in Vermont and elsewhere in North America, and then set each one free to fly toward Mexico, where many are later encountered by conservationists searching for the buttterflies once they arrive in Mexico. With each recovery, we learn more about Monarchs and how they migrate.
The “Heavy” Hydrogen
Dragonflies aren’t so obliging. For one thing, we’re clueless about where they go. Monarchs concentrate each winter in stands of Oyamel Fir in mountains west of Mexico City. So we know where to find them and how to protect them. Tagging or somehow marking a dragonfly would be like putting a message in a bottle and tossing it out to sea. Actually, I suspect we’d find the bottle before the dragonfly.
Yet it turns out that we need not tag or otherwise mark these migratory dragonflies because they themselves carry clues about where they have been. If the Merlin doesn’t get it first, we can catch any migrating dragonfly, analyze trace elements in its tissue and determine roughly how far it has flown.
Our marker is water, more to the point the two hydrogen atoms in water. Recall from high school chemistry that hydrogen nucleus normally contains a single proton and no neutron. But a tiny fraction of hydrogen atoms around the world carry one proton and one neutron. We call it “heavy hydrogen,” or deuterium. And unlike other such atomic variations among elements (which can be radioactive), deuterium is stable in the environment – a “stable isotope”– and stable in the wing of a dragonfly.
The amount of deuterium in water varies somewhat predictably in North America. You can map it. The ratio of deuterium to hydrogen in water falling as rain or snow changes on a gradient corresponding roughly with latitude. Water in Alberta, for example, carries a different deuterium-to-hydrogen ratio than water in Alabama.
Because dragonflies grow up as nymphs in water, they incorporate the local deuterium ratio into their tissue. It’s like a dialect or an accent that a dragonfly bears for life – whether as a nymph in water or a free-flying adult in migration. A Common Green Darner on the wing over Mt. Philo or Miami unwittingly carries a particular deuterium ratio, a birth certificate that tells us generally where it grew up. You are what you eat – or drink.
This science isn’t perfect. We can’t pinpoint a dragonfly’s natal waters in the way we know where a banded bird hatched or a tagged Monarch emerged. But stable isotopes are helping us track the range of migrating dragonflies. It’s “better living through chemistry.” After all, we can’t really know a bird or butterfly or a dragonfly – and what it might need in the way of conservation – until we know all the places it lives or wanders.
By the way, you need not be a chemist to help track dragonfly migration. We’re counting dragonflies in the same way we count migrating raptors during hawkwatches each fall. Learn how to do it and report what you find with help from the Migratory Dragonfly Partnership.
And while we’re out there counting, if a Merlin happens to catch a dragonfly first, we can still make a difference … by catching one of those dragonfly wings floating toward Earth.
Bryan Pfeiffer is a writer and field naturalist who specializes in birds and insects. He teaches writing in the University of Vermont’s Field Naturalist and Ecological Planning Programs.
By Joanne Garton
It has happened countless times: I walk into my favorite restaurant only to find that it is out of breakfast burritos. The manager points me to the tamales without ever explaining if it was a lack of eggs, a problem with the oven, or an angry mob of hungry burrito-eaters that wiped out the supply this weekend. I leave hungry and find somewhere else to eat.
These days, the red knot birds in Delaware Bay are similarly exasperated, but with no other food to eat when their seasonal feast of horseshoe crab eggs are gone, the migratory birds are starving. Horseshoe crabs are the favored bait for a growing market of eel and conch farms, diminishing the supply and diversity of breeding horseshoe crab pairs left in the bay. Continue reading
April showers bring more than May flowers, and birds aren’t the only creatures producing fantastic choruses in the springtime. While birders will set their alarms for 5:00am in order to catch the rainbow of spring migrants arriving in Vermont, herpetologists – that is, aficionados of amphibians and reptiles – will spend the wee hours of the night up to their knees in muck and water to glimpse the bizarre courtships of frogs and salamanders.
Beating wings fill my view. The snow geese are stark white, and the black tips of their wings pulse in contrast with their bodies. Hundreds – no, thousands – of these meaty birds move in unison. They squawk and honk, thousands of calls melting into an urgent and persistent roar.
At least that’s what I envisioned.
I had never seen snow geese, but I set out confidently to find the birds. I wanted to feel the wind from a thousand birds taking off at once. I wanted to feel their thunderous calls in my chest. Continue reading
by Cathy Bell
(originally posted on vtdigger.org)
Every autumn, thousands of snow geese take a break from their 5,000 mile southbound migration to rest and feed at Dead Creek Wildlife Management Area in Addison, Vermont. Journeying from their breeding grounds on the Arctic tundra to their winter range in the mid-Atlantic and southeastern states, the snow geese are but fleeting visitors to the Green Mountain State, descending on our cornfields from October into early November.
The bright white feathers of a snow goose’s body contrast with tips of the wings, which look as though they have been dipped in paint of the richest black. Young birds are brushed with gray on their backs, giving them a dirty appearance. Here and there among the flocks are dark gray individuals with white faces. These steely-looking birds, commonly known as “blue geese,” are the same species as the white ones. Snow geese of either coloration are far prettier, to my eye, than our resident Canada geese. Getting to see these visitors from the north is a seasonal treat.
Hoping to find some snow geese, I went to Dead Creek on Saturday, October 30. The day started out sunny but clouded up as the big Halloween nor’easter worked its way towards New England. Driving down Route 22A from the north, I made a right turn onto Route 17. I had gone less than a mile from Addison Four Corners when I saw a wheeling flock of waterfowl. Backlit, the winged forms did not reveal any details of their plumage, but the size and flight pattern didn’t seem quite right for Canada geese. Even as I thought to myself that I must be in the right place, I saw a turnoff on the south side of the road. I pulled off the highway, shut off the ignition, and hopped out of the car, binoculars in hand. Looking to the south, I felt my jaw drop in wonder.
About 800 geese were in a field very close by, in easy sight of a viewing platform with interpretive signs. Hundreds more were in a distant depression. From the knot of people with binoculars and spotting scopes a quarter mile to the west, I guessed there was another—possibly even bigger—group of geese over there too. Aerial photo counts that weekend documented more than 4,600 geese in the area, but few people braved the chill wind of the gray afternoon to witness the impressive spectacle.
A northern harrier, its white rump patch catching the watery light, startled the nearest geese into rising from where they rested and fed. Within moments, the nervousness of a few waterfowl swept through the flock, and hundreds of birds were in the air, honking their discontent in a higher-pitched and more tremulous voice than that of the familiar Canada goose.
Though I looked carefully, I failed to find any Ross’s geese among the swirling clouds of white waterfowl. Snow geese and Ross’s geese are two distinct species, though very similar in appearance; the rarer Ross’s is more diminutive in build and has a smaller bill. I later read on the Vermont bird listserv that there were indeed two Ross’s geese at Dead Creek that afternoon, but they were the needles in the haystack of thousands of snow geese.
I may have lucked into witnessing the peak of this year’s snow goose migration, but there’s still time for you to see the spectacular waterfowl as they pass through Vermont.
At 2,858 acres, Dead Creek Wildlife Management Area is administered by Vermont Fish and Wildlife and includes extensive reaches of cattail marsh and stretches of open water. The geese, however, are concentrated in upland agricultural fields. The designated goose viewing area along Route 17 is the best place to see the birds, but a little farther south, Gage Road can provide good sightings as well.
Moreover, though the snow geese may be the star attraction, there is more here for inquisitive visitors to enjoy. Northern shovelers and green-winged teal dabble in the shallow, ponded water of the fields, and once in a while a pectoral sandpiper passes by overhead. A quarter mile west of the goose viewing turnoff, Route 17 crosses the still, murky waters of Dead Creek. Mallards and black ducks ply the waters here. Just over the bridge, a left turn takes you down a gravel road towards a hunters’ camping area. Look along the reedy edges of the water for great blue herons and wood ducks. Despite its name, Dead Creek is a lively place.
The creek flows northward, parallel to the southernmost portion of Lake Champlain. Just seven miles north of where it flows under Route 17, the creek joins with Otter Creek and soon wends its way into the lake. Its meandering path has been modified by the addition of dams, and today, the state actively manages water levels in the flooded impoundments.
The snow goose hunting season runs from October 1 – December 29 in the Lake Champlain waterfowl hunting zone, with a daily bag limit of 25 birds. Portions of the Dead Creek Wildlife Management Area, including the upland areas south of Route 17 near the viewing area, are managed as a refuge where no hunting or other public access is permitted.
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.