By Tony Gazso, Interpretive Naturalist

As fall begins to turn to winter, a different type of migration is under way. Most of us think of migration as the same birds moving to the same areas every single year, but some are likely unfamiliar with an irruptive migration. Just what is an irruption? Well, in terms of birds, an irruption is when a species migrates to an area in large numbers based mainly on food supply rather than a hormonal change. What this means is migration for these species is dependent on food supply and can be highly variable depending on the year. 

Common redpoll

One of the best examples is the pine siskin. A small streaky-brown finch with bright yellow wings, the pine siskin is a finch of the Canadian boreal forest. Every year, they migrate to the northern U.S. in small numbers. Some years, you won’t see any at all. But in years where the seed crop is low, these little birds head south in much larger numbers (and fly further south than normal). This year happens to be one of those years! Thanks to a very small supply of conifer seeds in Canada, pine siskins have irrupted into the U.S. in huge numbers. In fact, Audubon reports that this has been one of the biggest irruption years ever recorded for these finches! They’ve been seen across our area by the dozens, showing up in backyard feeders and across the parks. So many have been migrating that there are even reports of pine siskins as far south as Bermuda!

Pine siskin

Pine siskins aren’t the only irruptive birds that visit our neck of the woods either. In fact, they’re simply one in a line of irruptive birds we have seen in Ohio this year. Earlier in the fall, we saw an irruption of red-breasted nuthatches, and there is currently an irruption of evening grosbeaks in the parks! These striking yellow, gray and black birds rarely visit Ohio in non-irruptive years. Other irruptive species we could find in our area include common redpoll (a small plump finch with a black mask and red forehead), pine grosbeak (a large red and black finch), white-winged and red crossbills (finches with unique beaks), and even a bohemian waxwing (a grayer version of the resident cedar waxwing). 

Evening grosbeak

It’s not just songbirds that can be irruptive either. Birds of prey, such as rough-legged hawks and short-eared owls can also be irruptive, showing up in larger numbers some years. And just like the pine siskins, there have already been quite a number of short-eared owls spotted in our area. In raptors, owls in particular, the evidence seems to show a trend to irrupt more when there has been more food rather than less. The theory suggests that higher mammal populations during breeding season leads to more productive nesting, and thus more birds in general. When the mammals become scarce as winter approaches, there are more owls than available food, so they wander south in larger numbers in search of food. Irruptive years bring some excitement to what is usually a rather dull time of year, at least in terms of birding. So watch your feeder–you just might see something unique! 

Red-breasted nuthatch

Rough-legged hawk

Short-eared owl