This winter is shaping up as a great irruption year all across the Midwest and the Great Lakes states. This is a very exciting event for bird watchers and naturalist. But before you go running for your dictionary or complain about my spelling (which is terrible, I agree) yes, I am talking about irruption with an “i”.
The term irruption is a term used to explain when birds that don’t normally migrate, move or “irrupt” out of their normal range. Typically this movement is south but not necessarily. They could move east or west and rarely north.
The main reason behind this kind of movement is not completely understood but it most likely has something to do with the available food supply. When a particular food supply such as spruce cones which are packed with dozens of seeds, are in short supply the birds quickly exhaust the meager source of food and are forced to irrupt in search of a new food source.
Another explanation of irruptive behavior is when a specific population of bird becomes too numerous. If reproduction from the previous spring was exceptionally high and there are many new members of the flock, this can also trigger the birds to irrupt.
Not all bird exhibit irruptive behavior. Some of these birds include the Pine Siskin, the Common Redpoll and White-winged Crossbills. These are the three species most commonly seen this winter. There are also several species of owl that exhibit irruptive behavior such as the Great Gray and Northern Hawk Owl.
None of these birds migrate in the typical fashion nor do they irrupt out of their regular range each and every winter. Irruption is usually restricted to every 3 to 5 years without much of a set pattern. Some birds such as the Northern Goshawk, which relies heavily on Snowshoe Hares and Ruffed Grouse for their main food supply, are on a fairly regular time table of irrupting–every 10 years. In these cases the snowshoe and the grouse population go up and down in ten year cycles. As the population of the prey, in this case the hares and grouse, becomes scares the Goshawk irrupts out of their normal range and moves south in search of better hunting.
Most of these irruptive birds are northern birds that typically live in the conifer (evergreen) forests of Canada. It’s when we have a failure of the spruce and fir cone crop that we see the movement. In fact based on the cone crop we are able to make some fairly accurate predictions of which species are going to irrupt and in which region they will irrupt from.
Small irruptions happen all the time and we often don’t notice. However when there is a massive cone failure across a wide region it effects many more birds and we see the results of a lot of birds visiting our feeders as we are this year.
What I find ironic about this is the cone crop which matures in the fall start as flowers that need to be pollinated in the spring. So in other words, if we have bad weather in the spring and the conifer trees are not pollinated we won’t see a very good cone crop. So the weather from 6 or 8 months prior is causing the birds to move now in the middle of winter. This is another great example of the interconnect-ness of nature.
It’s been a great year for many of these irruptive species. Many backyard feeders are being inundated with hundreds of Common Redpolls and Pine Siskins. I know at my feeders, I am filing up the thistle nearly every day. I am amazed at how quickly they can clean out a feeder that is filled with tens of thousands of tiny seeds.
Another great sight this year is the flocks of White-winged Crossbills. These handsome large birds descend upon our spruce and pine trees in flocks of 20 or 40 and clean out all of the available cones. The males are bright red and the females are a dull yellow to gray. As their name implies they have bills with upper and lower mandibles that cross, giving them a scissor-like effect to cut the seeds free from the cones in a very fast and efficient manor.
So if you have any of these birds coming to your feeders or you are seeing the crossbills feeding in your conifers take a moment to enjoy them. It may be several years before they irrupt again. Until next time…