Thursday, November 22, 2007

Upcoming events

Shameless promotional message: I'm scheduled to appear Thursday, Nov. 29, on NPR's "On Point" program, from 11 a.m. to noon EDT. I'll be discussing my new book, Of a Feather, a history of birding and ornithology in America.

That weekend, I'll be giving the keynote for the Ohio Bird Conservation Symposium at Deer Creek Resort south of Columbus, and sponsored by the Ohio Ornithological Society and The Nature Conservancy. And on Tuesday, Dec. 4, I'll be addressing the Birmingham (Alabama) Audubon Society.

Hummingbirds in the snow

Hummingbirds in the snow…I'll admit, that seems like an avian non sequitur, since everyone knows that hummingbirds are the jewels of summer, little tropical hothouse birds that would faint at the first hint of cold weather, never mind an actual flake or two of snow.

Which is why I especially love days like this past Sunday, when I was driving over the Kittatinny Ridge in heavy snow showers. Down in the valley an hour south of my house it was slightly warmer, and the snow was coming down as rain, while I set up a cage trap on the porch of a lovely old 1800s farmhouse. A nectar feeder hung inside, and within minutes, I'd trapped an immature female Selasphorus hummingbird, which Deb and Jim, the homeowners, had spotted a couple of days earlier.

If that seems remarkable, it isn't; western hummingbirds have become commonplace in eastern states like Pennsylvania every fall and winter, often lingering until well past Christmas, and through nights when the temperature may dip below zero.

In fact, the only remarkable thing about this situation was that this was the second hummingbird to show up at Deb and Jim's home this month. A week earlier, my colleague Wayne Laubscher of Lock Haven (covering for me while I was out of town) had banded an immature male rufous hummingbird here, a sparkling bird the color of a new penny, with its fiery orange gorget almost completely molted in. The little guy was still hanging around on Sunday when I was there, and buzzed us a couple of times after we had the trap set up.

A rufous hummingbird, banded in late December 2004, Middletown, PA (©Tom Johnson)

Once I had caught the new hummer, it was a matter of about five or 10 minutes to band her, take a few measurements, some photographs, and then release her. The measurements allowed me to make a firm identification; female and immature hummingbirds of the genus Selasphorus are almost impossible to identify in the field, but by measuring the width of her outermost tail feathers, her wing and bill, and by looking for a distinctive notching in one of the central tail feathers, I confirmed that she was a rufous hummer, and not one of the look-alike Allen's or broad-taileds.

Wait a minute, though – what would any of those decidedly western species be doing in Pennsylvania, especially on a snowy, late-November day? The answer appears to be bound up with the rapid development of a new migratory route, and a glimpse of avian evolution in action.

Traditionally, all of these species – rufous, Allen's, calliope, black-chinned, broad-tailed and others – nested in the U.S. and Canada but wintered primarily in Mexico. To get there, they follow a genetically coded orientation that propels them south in fall – flying individually, not in flocks or with their parents, depending solely on the instinct inscribed in their DNA.

But DNA mutates, and when it does, sometimes you get birds that head in the wrong direction. That's probably what's happening with these hummingbirds; programmed to head east instead of south, they wind up in the mid-Atlantic states in autumn, then work their way down to the Gulf Coast, where thousands and thousands of them now pass the winter.

By catching and banding these birds, which may be recaptured miles or years later, we can document this evolution of a new migratory route and wintering ground. I'm one of a loose network of hummingbird banders in North America studying this phenomenon, and at this time of year, I'll drop everything to race out and band a newly reported hummingbird.

On Wednesday I drove to northern New Jersey to band what is only the fifth calliope hummingbird to be seen in the Garden State. This little immature female (calliopes, which weigh about 3 grams, are the smallest birds in North America) was snugged down in a small but lavishly landscaped backyard in Denville, where dozens of birders had been coming to see her.

She was a snap to capture, and calm in the hand as she got her own, custom-made band, a minute thing only 5.4mm long, hand-crafted into a neat circle and laser-printed with a serial number, N99797. The bands are so small it takes more than 5,500 of them to weigh an ounce, and are no hardship for the bird.

Within a few minutes of her release, she was feeding again at one of the feeders, her movements followed by several big telephoto lenses. At night, like all of these cold-hardy westerners, she'd be tucked in a dense thicket, where she'd turn down her internal thermostat from a daytime high of about 109F to about 50F, going into a profound, death-like torpor to save energy. (That's why these western hummingbird species, which can be found above 9,000 feet in the Rockies and as far north as the Kenai Peninsula in Alaska, are not bothered by sub-freezing temperatures in the East. If they're healthy, they can even tolerate lows below zero for a few nights.)

A couple of times she zipped out from her perch to snag a small, passing insect – even in cold weather, these birds are adept at finding invertebrates, often picking dormant bugs out of foliage and from the crevices in bark. Nectar, either natural or from a feeder, makes up less than half of their diet at all times of the year.

The calliope was in good shape, except for some missing throat and tail feathers, perhaps from a collision with a wire or twig, which she would soon replace. And I was just in time – she apparently left this morning, Thanksgiving, a lovely, mild day and a perfect one for heading south. She took with her a tiny band – and my thanks, naturally.

Wednesday, November 7, 2007

The Flood from the North

The boreal forest is emptying out – I can see it at our feeders, and every night we see it in our owl nets.

Last year, the forests of eastern Canada provided an incredible bounty of food, in the form of mast – the broad term for nuts, berries, pine and spruce seeds. Many trees "mast" unpredictably, as a strategy for thwarting seed predators like birds and mammals; some years they bear very little, keeping predator populations low, then they will flood the market, so to speak, with vast quantities of mast, so that at least some of the seeds will survive to germinate.

As it happens, 2006 was a year when most of the species in the eastern boreal forest heaped the table with a feast – mast in great abundance. Many species of seed-eating birds, like finches, nuthatches and chickadees, stayed north.

Because the mast provided food for huge numbers of mice and voles, many northern owls also stayed home last fall and winter, and those of us who band migrant saw-whet owls down here in the eastern United States had our worst season ever.

But my, how things have changed. This fall, the trees of eastern Canada shut off the spigot; the mast crop was meager to nonexistent in many areas. Faced with poor prospects, many northern birds have been flooding south in a phenomenon known as irruption (the term is the opposite of eruption – a rushing into, as opposed to an explosion out of, something).

Irruptive birds include purple finches, pine siskins, red and white-winged crossbills, common and hoary redpolls, red-breasted nuthatches and pine grosbeaks. They also include many northern raptors, among them northern shrikes and a variety of owls. Unlike most migrants, which travel predictable routes at predictable seasons, the irruptive species strike like lightning, appearing and disappearing as though on a whim.

(This has nothing to do with the severity of the coming winter, by the way. The last really good winter finch year we had down here, back in the late 1990s, was also one of the warmest on record. It's all about food, not temperature.)

But with the food growing scarce, the birds are getting out of Dodge. Night after night, my crew of owl banders have been catching record numbers of saw-whet owls, up to 75 in an evening. These birds have been in exceptionally good condition (we check their fat stores and muscle mass), but if they'd stayed north, chances are they might have starved.

Birders here in the mid-Atlantic states are also excited by the arrival of large numbers of northern finches and other seed-eating species. We noticed a huge influx of black-capped chickadees and white-breasted nuthatches starting in late August, and in recent weeks additional boreal species have been coming in; this morning, purple finches and a red-breasted nuthatch, both irruptive species, joined the melee at our feeders.

This past week, there have even been growing numbers of reports of evening grosbeaks across Pennsylvania, a stunning species that was unheard of in Pennsylvania prior to 1890, but which began to invade the state in winter more and more frequently, and in greater and greater numbers, in the early decades of the 20th century. Many of us remember fondly their biennial invasions in the 1960s and '70s, when they would crowd feeders, sometimes by the hundreds, consuming vast quantities of sunflower seed and earning the nickname "gross-pigs" from birders who got tired of shelling out for so much food.

Then, they were gone. Since the 1980s, evening grosbeaks have been almost completely absent from our region. In this case, though, there is more at work than simply the boom-and-bust cycle of northern mast production.

Evening grosbeaks nest across the boreal zone from Newfoundland to British Columbia, and south in high conifer forests into southern Mexico. Across much of their range, a favorite summer food is a moth larvae known as the spruce budworm, a cyclical species that can reach plague dimensions in spruce forests.

Many boreal songbirds depend upon spruce budworm, including Cape May and Tennessee warblers. Like the grosbeak, their populations rise and fall in lockstep with the fortunes of the budworm. The last time we had lots of grosbeaks coming south into the eastern U.S. was during a spike in the budworm cycle in the 1960s and '70s, when millions of acres of across Canada were defoliated. But since then the caterpillars have been on the wane, and the populations of many of these budworm specialists have been on the decline as well.

So while the lack of mast this year is obviously driving the grosbeaks south, they will probably not come in the great numbers I remember from my childhood, because there just aren't that many grosbeaks these days.

There may be more at work with the grosbeaks than simply the budworm cycle; while research in eastern Canada suggests evening grosbeaks are strongly linked to budworm numbers, that doesn't appear to be the case in part of the West. And in fact, there is evidence that at least some of the irruptive grosbeak flocks that reached the East in the good old days were actually from the West, crossing the Plains and eating the seeds of box-elders, planted in shelterbelts across the prairies.

There is still a lot to learn about this beautiful finch, but for now, I'm just keeping my fingers crossed, hoping that a few will show up at our feeders.