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/

An Epic Bird Finding Guide

We hiked up a steep incline to arrive at a beautiful wildflower meadow.  The brilliant oranges and reds of Indian Paintbrush contrasted starkly with the bright white Beargrass.  We had chosen the Iceberg Lake trail in Glacier National Park because of the enticing description in our birding guide, “Glacier is for the Birds.”  From our lofty perch, we scanned the tops of the extensive spruce/fir forest in the valley below us.  We could see numerous waterfalls and cliff faces covered in wildflowers on the mountainsides around us.  Suddenly, an iridescent caramel-colored speck whizzed up the valley.  The male Rufous Hummingbird landed at the top of a nearby spruce, giving us fantastic studies of its sparkling gorget and back.  We were quickly distracted from our quest to get a photo that really showed the iridescence of the hummingbird by the call of a Dusky Flycatcher coming from further upslope.  We soon found the bird perched in the top of a bush, but I listened more than I looked, as Empidonax flycatchers are extremely hard to identify by sight.  “Glacier is for the Birds'” predictions were proving amazingly accurate: “As you proceed through the shrubs and until you head back into the trees, listen and watch for Dusky Flycatchers, Orange-crowned Warblers, MacGillivray’s Warblers and Lazuli Buntings,” though we still hadn’t seen any Lazuli Buntings.  After more searching of trees and listening for calls, we finally located a male Lazuli Bunting singing in a bush.  After the first one, they seemed to be everywhere, and we enjoyed many views of this spectacular bird.

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Lazuli Bunting (Passerina amoena)

We paused every mile or so and checked the book again, as it provided so much detail we couldn’t remember it all.  Next was “Past the Red-rock outcrop, look for Pine Grosbeaks until you are in the trees.”  As soon as we had fully rounded the next big projection of Glacier’s famous “red rock,” a male and female Pine Grosbeak flew off the path into the top of a large fir.  They stayed there only a few seconds, giving us just enough time to get a decent look, and then flew away.  That was the only time we saw Pine Grosbeaks on our trip.

My experience in Glacier National Park convinced me that a good bird finding guide is essential for travel, even though I usually rely heavily on eBird for local birding information.  EBird is a global citizen science project by the Cornell Lab of Ornithology that gathers birders’ sitings into a massive database, which they make available to the public.  I have been eBirding since I started birding, and I can’t imagine birding without it.  EBird is a fantastic tool for keeping personal lists, finding target birds, and learning basic information about a location, but you still really need an actual book.  Some regions are poorly ebirded, leading to small and useless amount of data.  Some regions lack solid internet connection (like Glacier), making it impossible to use.  EBird also lacks the level of detailed information about bird finding often found in bird finding guides.    For instance, on one hike we did to find Timberline Brewer’s Sparrow, our book told us not only which trail but exactly which switchback to look for the sparrows’ territories.

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Brewer’s Sparrow (Spizella breweri)

Finding the Brewer’s Sparrow wasn’t the only time the guide proved so precise it made our jaws drop.  One of the few target birds we hadn’t found by the end of the trip was the Evening Grosbeak.  The guide recommended a brief hike at Goat Lick for it.  We decided to stop there on our last day heading out of the park.  That day ended up full of excitement (see previous post) and we felt like we had to skip the Goat Lick hike as we figured we couldn’t afford the time to look for the bird.  As we were driving, we saw a crowd gathered on the side of the road.  Was it a bear jam, we wondered?  Nope, it was goat jam.  A family of five Mountain Goats were standing right next to the road!

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Mountain Goat (Oreamnos americanus)

After a week of being in the park, we had seen many Mountain Goats, but they had all been distant specks way up on ridge tops.  Apparently, they come from miles away to Goat Lick to ingest minerals from the rocks like calcium, phosphorus, magnesium, and sodium.  The opportunity to photograph these amazing animals was too good to miss.  I didn’t even bring my binoculars, not knowing this was also the place mentioned in the book for Evening Grosbeaks.  Soon, the goats moved under the bridge and out of sight.  As we were about to go, a little yellow-and-black blob flew up the canyon, chittering wildly, and landed in a spruce near the bridge.  It was immediately followed by four more Evening Grosbeaks.  They were so close and bright, I didn’t really mind not having my binoculars.

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Evening Grosbeak (Coccothraustes vespertinus)

One of the things that made this bird finding guide so accurate was it was super up to date, published only last year.  Most of the birds he talked about still occupied the same territories they did last year, although I don’t really know they were the same individuals.  Older guides can still be useful, though.  On a trip to Florida last winter, I purchased the ABA/Lane “A Birder’s Guide to Florida,” by Bill Pranty, published in 2005.   I was saddened and disappointed several times during our trip when the birds he mentioned were gone and the described habitat looked very degraded or had even disappeared all together.   But despite being more than 10 years old, it was still full of great information, detailed directions, the authors personal advice, and great maps in a portable, accessible format.    In combination with eBird, it was very helpful in planning and accomplishing our trip.

One time in Miami, I looked on eBird for recent reports of Cave Swallows, a species that I really wanted to see.  There were no recent reports, but the bird finding guide had a nearby bridge staked out as a Cave Swallow nesting site.  Was it possible, 10 years later, that there could still be swallows under that bridge that hadn’t been reported on eBird? We drove quickly into the growing darkness to find out.  Upon arriving, my first impression was of an old, deserted bridge over a filthy canal, surrounded by busy highways.  Not a hopeful sight.  We searched the canal, under the bridge, and the surrounding area but saw no birds.  As we were getting ready to leave, my brother, lagging behind as usual, called from under the bridge that he saw a Cave Swallow.  He used his flash to illuminate the dark underside of the bridge once we were ready, and for just a second, I saw a little nest with a Cave Swallow peeping up out of it.