Winter Bird Irruption

Many species of birds, including raptors, warblers, waterfowl, shorebirds and sparrows migrate twice each year, south in fall, north in spring. Not all birds migrate to the same places each year though. Some birds that breed in the boreal forests of the north come as far south as the Mid-Atlantic states only occasionally, after an absence of several winters. These irregular southward migrations are known as irruptions. Unusually large numbers of several of these “irruptive” species have reached Virginia this winter, including such beautiful birds as purple finches, red-breasted nuthatches, and evening grosbeaks.

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Purple Finch

Other irruptive species include boreal finches, like pine siskin, red and white-winged crossbills, common and hoary redpolls, and pine grosbeaks, as well as certain species of owls and raptors, such as rough-legged hawk, northern goshawk, and snowy owl. Black-capped chickadees also irrupt. These northern species rarely all come south in the same years, but it is not uncommon to have years when multiple species have large coordinated movements.

Irruptive birds move south when there is not enough food to support their populations in the north. The finches, red-breasted nuthatches and black-capped chickadees fly south because of bad conifer cone crops in the boreal forest. Snowy owls, on the other hand, seem to irrupt in years when their prey, lemmings, are particularly abundant. While these irruption triggers appear contradictory, they really are not. In both cases, relative scarcity of prey to predators causes a food shortage. The snowy owl population explodes from the plentiful food to the extent that the lemming population can no longer support them all come winter, so they come south in search of food.

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Pine Siskin. Photo by Drew Chaney.

Irruption is closely tied to a cyclical fluctuation in the seed crops of trees the birds depend on as winter food sources. Birches, alders and conifers in the boreal forests— all important food sources for irruptive songbirds — do not bear equal seed crops every year. “Mast” years when lots of seeds are produced are followed by several years of poor seed production. This appears to be an evolutionary strategy to limit the populations of creatures that eat the trees’ seeds to ensure the maximum possible number of seeds survive. In good seed crop years, seed eaters do well, and their population expands. When the next year’s crop is poor, there’s even less food for each animal than there would have been if the population hadn’t grown the year before, and the population falls. Then, when the next good year comes, there are not enough animals to fully capitalize on the seed crop, and some seeds escape. Oaks, hickories, and beeches in the deciduous forests of the East have similar cyclical fluctuations in seed production.

The winter of 2018-2019 is an irruption year for many species of boreal birds. Red-breasted nuthatches started moving south into Virginia as early as August. I saw my first of the season on August 19th in Sussex County. By September they were abundant throughout the state, with several migrating individuals being observed each day at the Rockfish Gap Hawk-watch in Augusta County. Starting in September and October, the nuthatches were joined by large numbers of purple finches and pine siskins. Numbers of these three species dropped significantly by December, but they remained present throughout the state. Many evening grosbeaks and even a couple of common redpolls have also been found in Virginia this year.

Few of the irruptive finches are as beautifully colored or as interesting as the evening grosbeak. Evening grosbeaks were fairly rare in eastern Canada over 100 years ago. Their population exploded about 60 years ago, which corresponded to a major outbreak of their preferred summer food — the spruce budworm. During the mid to late 20th century, they irrupted in huge numbers, sometimes with hundreds in Virginia at once. Since then, their population in the East has crashed, possibly due to habitat reduction from logging in the boreal forest, increased diseases, or decreased spruce budworm populations. As the evening grosbeak population has declined, they’ve irrupted in smaller numbers. So far, this winter has been relatively great for them though, with many having been seen at feeders around the state.

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Evening Grosbeak

Bird feeders are a particularly good way to see some of the beautiful finches that will be visiting our region this winter. Almost all of them like black-oil sunflower seeds. Pine siskins and redpolls — if we should be lucky enough to have more of them this winter in Virginia — particularly like nyjer or thistle seed. My brother and I recently put up a large platform feeder full of black-oil sunflower seeds in hopes of attracting an evening grosbeak, as they apparently prefer platform feeders to tube feeders. In all probability, we won’t see one on our feeder this winter, but you never know!

Sources

Pittaway R. (2014, September 20). Winter Finch Basics. Retrieved from http://www.jeaniron.ca/2012/winterfinches.htm

Pittaway R. (2018, September 20). Winter Finch Forecast 2018 – 2019. Retrieved from http://jeaniron.ca/2018/wff18.htm

Ehrlich P. R., Dobkin D. S., & Wheye D. (1988). Irruptions. Retrieved from https://web.stanford.edu/group/stanfordbirds/text/essays/Irruptions.html

Shaw D. W. Bird Irruption: A Sudden Surge of Birds. Retrieved from http://www.birdsandblooms.com/birding/birding-basics/bird-irruption-surge/

Cornell Lab of Ornithology. Evening Grosbeak Life History. Retrieved from https://www.allaboutbirds.org/guide/Evening_Grosbeak/lifehistory

Mortensen R. (2012, November 7). Birders Can Contribute to Evening Grosbeak Science Right Now! Retrieved from http://blog.aba.org/2012/11/birders-can-contribute-to-evening-grosbeak-science-right-now.html

Devokaitis M. (2018, November 6). This Could be the Winter You Get Evening Grosbeaks at Your Feeder. Retrieved from https://www.allaboutbirds.org/this-could-be-the-winter-you-get-evening-grosbeaks-at-your-feeder/

Blue Ridge Young Birders Winter Field Trip to Northern Virginia

We stood shivering in the 22 degree early morning air, looking out on the partly frozen Potomac River.  To our left, we could see the smokestacks and apartment buildings of the District of Columbia, while across the river to our right the thick forests of Maryland loomed.  A thin coating of snow lay on the ground, extending out onto the ice of the Potomac.  Far out on the unfrozen parts of the river, a few-hundred ducks huddled, periodically diving or dabbling.  Occasionally, a group of common mergansers flew overhead, their green or brown heads contrasting sharply with their white necks and bodies.  A sleek, camouflage covered boat drifted out onto the river, carrying two duck hunters towards the distant rafts of ducks.  Stirred to action despite the cold by the fear that the hunters would scare the ducks out of sight, we resumed scanning through our scopes.  Two lesser scaup and a few ruddy ducks dove up and down near the sides of a large group of over fifty canvasbacks.  Mallards made up most of the second, larger raft, with other dabbling ducks like American black duck and gadwall mixed in.  Behind these ducks, on the very horizon of what we could see clearly, more diving ducks drifted and dove.  Logan said that he had a long-tailed duck, one of the rare species we were looking for here, in his scope.  I looked in his scope and saw it, but before anyone else in our group had the chance, a gunshot sounded out on the river and all the diving ducks lifted off and flew far across the river into Maryland.

We walked down the road to the Dyke Marsh Wildlife Preserve, where we hoped to see more ducks and other birds.  To our left stretched acres of the last freshwater tidal marshes next to the Potomac, and to our right grew a beautiful mature swamp forest.  As we walked in, the thickets and clumps of vegetation along the path were hopping with song, white-throated, and fox sparrows.  Swamp sparrows flitted and chipped in the marshes.  The path eventually emerged out of the woods and onto a little peninsula that stuck out into the river.  We saw many more ducks from here, mostly diving ducks such as lesser scaup, ring-necked duck, canvasback, redhead, and common mergansers, and of course, the ever present mallard.  Baxter, Shea, and my brother Theo decided to walk across the peninsula on a boardwalk to check the other part of the river.  They soon called that they had a long-tailed duck.  The rest of us rushed over the boardwalk, heedless of the slippery snow that coated it.  There turned out to be two female long-tailed ducks, quietly swimming about on the other side of a small cove, barely ten yards away.

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Long-tailed Ducks (Clangula hyemalis) are typically a coastal species during the winter, so seeing one inland on the Potomac River is certainly note-worthy.

The diffuse winter morning sun lit the ducks from behind us, creating a gorgeous medley of rich colors.  One of the ducks seemed to have a belly itch, because it kept turning upside down in the water and preening its belly in a rather comical fashion.  It would sit upright in the water, and use its feet to keep it from falling over, making it swim backwards in a vertical position.  Here is a video Theo got of this preening behavior.

 

 

On our walk out of Dyke Marsh, we counted 10 fox sparrows, which is the most I have ever seen at once.

Our next stop was the Laurel Hill Equestrian Area, to look for a clay-colored sparrow.  We followed the directions we had been given from the parking lot back down the road, past huge clumps and tangles of blackberry vines and grasses.  Soon we came to one such tangle, which happened to be the one the clay-colored sparrow favored.  As we walked around it, we saw a flock of white-crowned sparrows foraging next to the road.  The clay-colored sparrow was immediately apparent, as it was about half the size of the white-crowned sparrows.  Whenever the clay-colored sparrow got too close to a larger white-crowned sparrow, there would be a brief scuffle, followed by a flurry of snow, and the clay-colored sparrow would have to move further off.  Despite its low status in the flock, it behaved fairly well for us, and we all got great looks and photos.

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Clay-colored Sparrow (Spizella pallida), Photo by Theo Staengl

After a quick lunch, we headed over to Pohick Bay Regional Park, another place on the Potomac, where a Eurasian wigeon had recently been seen.  We walked out onto the river on a snow coated boat dock, set down our scopes, and began to scan.  Hundreds of gadwall formed the majority of the duck flock, with good numbers of American wigeon mixed in.  A humongous American coot flock swam a little bit further out.  Two horned grebes hunted behind the ducks.  We soon identified the Eurasian wigeon by its red head, and we all had descent scope views.

After a brief and uneventful stop at Occoquan Bay NWR, we drove to the Dulles International Airports parking garages, where we wanted to look for a continuing snowy owl and two rough-legged hawks.  From the top of the parking garage, we had an uninterrupted 360 degree view of the airport’s runways, but unfortunately this meant that there was no where to hide from the relentless wind.  Northern harriers and many short-eared owls hunted over the fields in the waning light.  Max soon found the snowy owl in his scope, perched on top of a distant airport terminal.  The 2017-2018 winter is shaping up to be a large snowy owl irruption, with birds already found in Franklin, Rockingham, Isle of Wight, Suffolk, King William, Accomack, and Loudon Counties this year.  It is very exciting to see these majestic northern owls so far from their home, using large farm fields and even airports as hunting grounds.  We stayed until the increasing darkness and the cold wind finally pushed us out, but despite seeing many red-tailed hawks, we could not find the rough-leggeds.  We got in the cars and started the long drive back to Charlottesville.