Wednesday, November 23, 2011

Crossbills and Irruptions

Winter often brings interesting things down from the North.  Snow, for one, floats in on cold arctic air that sweeps down from Canada. Earlier in the fall we saw many migrating birds on their way south for the winter.  They often stop in our wetlands and forests to eat and rest. We may also notice retired “snowbirds” migrating on the same routes, zooming along in motor homes and refueling at the nearest Holiday station.  Many birds, and snowbirds, migrate along the same routes every year, and their timing is so precise that phenologists can predict the arrival of the first and the departure of the last of each species to within a few days.

Other species are not so orderly, and seem to migrate helter-skelter in regards to date and location. Snowy owls, redpolls, and crossbills are a few examples of these “irruptive species.” To irrupt means to enter an area suddenly, in contrast to the lava erupting out of the volcano suddenly. We don’t see these irruptive species every winter, at least not in any quantity.  Most migrations are driven by food availability, and these are no different.  Have you ever noticed that our fair-weather bird friends are the ones who eat a lot of insects, especially flying insects?  Think of all those warblers, flycatchers, and robins! They skedaddle about the time I put away my insect repellant.

Our year-round residents tend to eat seeds or meat, which are easier to find in the winter than mosquitoes. Goldfinches and house finches are seed-eaters that we can enjoy all winter long. Chickadees must eat the energy-equivalent of about 250 sunflower seeds per day in winter! They don’t just eat seeds, though.  You may have seen them at your suet feeder or pecking at the fat on road killed deer.

Crossbills are finches that can survive almost anywhere and nest in any season, as long as they have plenty of spruce or tamarack seeds.  They are a classic irruptive species, which is why Katie Connolly, the Museum Naturalist (and my house mate), was so excited to see a white-winged crossbill in our yard this last weekend!  A quick check on the Wisconsin Birding List (, where lots of birders post their sightings, revealed that a hundred or more of these red birds with black and white wings were seen on the Bayfield Peninsula around the same time. 

Crossbills are fascinating creatures that I love to show visitors in the Museum’s Collections Room. In the cabinet of drawers that says “Please Open,” where we keep our study skins (dried bird skins stuffed with cotton), there lie two red birds with funny bills.  Just as their name suggests, their bills are crossed. The lower mandible curves under the upper mandible. They can be either “right-beaked” or “left-beaked,” but just as in humans, right-beaked birds are more common.

To eat, the crossbill slips its beak under the tightly shingled scales of spruce cones and then twists its head, using the curved tip to provide leverage. The scale is lifted just enough for the crossbill to grab the seed.  Crossbills often twist a cone off the tree and take it to a perch.  They extract seeds while holding the cone in one foot and rotating it like an ear of corn. A single crossbill can eat up to 3,000 seeds a day!

During this time of year it is common for flocks of humans to irrupt as well, often congregating in large and gregarious flocks where there is plenty of food. As winter closes in, we are reminded about what it means to share the bounty of this beautiful Earth, and to give thanks for all we have. Happy Thanksgiving!

For over 44 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M. The new exhibit, The Joy of Birds: Feathers in Focus opened in May, 2011. Find us on the web at to learn more about our exhibits and programs. Also discover us on Facebook, or at our blogspot,

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