Irruption species

By Claire Curry | Published Wednesday, March 21, 2012

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You may have seen on the local or national news that this is a big year for Snowy Owls.

Snowy Owls are big white owls that normally live in the high Arctic, cruising south to the northern United States and southern Canada at most in regular years. There have been several owls seen in Oklahoma this year, and even one in Texas at Lake Ray Hubbard. Those that have moved so far south are thought to be stressed and low on food, so they are often out during the day looking for food instead of hunting only at night as they normally do. Adult male Snowy Owls are almost pure white, while immatures (both male and female) and females have more dark blackish-brown bars all over their wings, back and belly.

Snowy Owls are not the only birds to make these irregular movements. Other species are also driven by fluctuations in food availability. Finches are particularly known for this. Even one of our common species, the Pine Siskin, has these movements (called “irruptions”). Some years you’ll see Pine Siskins are almost as abundant as goldfinches and other years there are few (I haven’t seen but one or two this year, for example).

Purple Finches also come and go. Some years we see flocks of the streaky brown females and the raspberry-purple males; other years there are none at all. They are often confused with our common and regular House Finches, which are a different shade of red in the males. Female House finches lack the white stripes of female Purple Finches on the face. Purple Finches have been declining in recent years.

Red Crossbills, another seed-eating wanderer, are rare here. We’ve seen them just a few times over the past decade, although in several cases the sighting was of a flock. Many forms of crossbills exist, each with a different-sized bill to eat different sizes of conifer seeds. Crossbills, as their name implies, have the tips of the bill crossed over to aid in opening conifers’ cones. They are so dependent on cone crops that they can nest at almost any time of year when they find a good food supply.

Common Redpolls and their pale northern cousin, the Hoary Redpoll (so named for its paler coloring), also wander. Wise County had the eight-state record in 2007. These tiny birds are streaked like a Pine Siskin but on a background of whitish gray with a strawberry pink wash over the face, a little black cap on the front of the head (like a male goldfinch) and a yellow beak. Hoary Redpolls have never been seen in Texas.

Evening Grosbeaks, large black-and-yellow seed-eaters, are also known for its irregular movements but usually do not occur this far south. Before the late 1800s, they were rare in the eastern United States but are thought to have spread their breeding range east with planting of certain trees that they like, such as box elder. They also like to eat seeds from ash, maple and locust according to “Lives of North American Birds” by Kenn Kaufman.

Other songbirds will irrupt, too. Red-breasted Nuthatches are particularly known for this. We had one Red-breasted Nuthatch at a feeder in our woods, and it stayed much of the winter. Other birders in the north-central Texas area saw more individuals that same winter.

Mountain Bluebirds are irruptive but tend to go eastward. They breed over much of the western United States and winter south into Mexico and east into western Texas and Oklahoma. I first saw them several years ago in their breeding range in Wyoming, but the most I have seen since then were flocks of 50 to 100 in southwestern Oklahoma, feeding on juniper berries in a wildlife management area just east of the Texas Panhandle.

The Cornell Laboratory of Ornithology has a website talking about some of these irruptive species: You’ll notice a trend that with both the seed-eaters and other birds, such as the owls, that food availability is the key to their movements. They all depend on food supplies that are irregular. Other migrants, such as warblers and buntings in the summer, are making a precisely timed trek toward resources that are generally dependable within certain limits (although of course there are sometimes bad years). You can view maps of all these species on There you can also report your sightings and contribute to our knowledge of the distribution and movements of these bird species.

Keep your eyes peeled at your bird feeders and beyond for winter irruptive species. You never know what you will see. Whether your sightings are common or rare, nature never ceases to surprise!


The next monthly field trips on the Lyndon B. Johnson National Grasslands will be Wednesday, April 4 and Wednesday, May 2. We will depart at 9 a.m. from the Forest Service District Office in Decatur. For more information, contact Mary Curry or the Forest Service District Office at (940) 627-5475.

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