An “irruption” of birds is when a larger-than-normal number of a species moves a longer-distance-than-normal in pursuit of food. In Maine, we see “irruptions” of northerly species that push south in large numbers in some winters. These irruptions are not due (directly) to weather, but due to a failure of food sources in their typical range. Therefore, when these birds exhaust their local food supply, they head elsewhere in search of sustenance.

If the berry and fruit crop is poor to our north, we may see large numbers of Bohemian Waxwings. If the vole population is low, we may see larger numbers of Northern Shrikes and Rough-legged Hawks. Bad year for lemmings = good year for us to see Snowy Owls. Last year, we saw an irruption of Red-bellied Woodpeckers that arrived from the south, possibly due in part to a low acorn crop in the Mid-Atlantic States.

“Winter Finches” are well known irruptive migrants. While Purple Finches and Pine Siskins do breed locally in most of Maine, large numbers occur in winter when seed crops (such as birch and hemlock) are poor. Common Redpolls irrupt on a near-biannual cycle, so this should be an “on” year for them – although last year northern Maine saw many more than is typical for an “off” year, so we’ll see if the pattern returns to schedule. Evening Grosbeaks, Pine Grosbeaks, and both Red Crossbills and White-winged Crossbills can also occur in larger numbers when specific seed crops to our north are poor. The same scenario goes for the Red-breasted Nuthatch.

Earlier this fall larger-than-normal numbers of Purple Finches and Red-breasted Nuthatches were being seen, and many folks are still seeing them in regular numbers. Observers as far south as New Jersey and Virginia were commenting on the unusual quantity of “Red-nuts” over a month ago, and now good numbers of Purple Finches are arriving in places like Cape May. So, it seems that something has caused Purple Finches and Red-breasted Nuthatches to irrupt this year. A seed crop failure? An extremely successful breeding season? Both? Something else? Who knows?

Lately, more Pine Siskins have been arriving in the area, so we’ll see if they follow this pattern as well. Common Redpolls are still a month or two off, if they show up at all, and it’s been quite some time since there has been an irruption of Evening Grosbeaks. So, get those feeders - especially the Nyger feeders - filled and ready to go. It could be an exciting winter at the feeding station!

So, is anyone else seeing large numbers of these species around Maine, or elsewhere? I’d love to hear from you! Let us know if you’re seeing Purple Finches, Pine Siskins, Red-breasted Nuthatches, crossbills, or Evening Grosbeaks in and around your yard. If so, do you usually have them at this time of year? Are you seeing larger than normal numbers now? You can use the “Post a Comment” field below this blog entry (and every other blog entry) to share your notes and comments. If I get a number of responses, I will try and synthesize them in an upcoming entry to try and decipher any patterns. I look forward to hearing from you!