When great grays are mentioned, anyone who has been around this area for awhile will immediately be reminded of the Great Gray Owl Irruption of 2004-2005. I've heard many stories of this irruption in the past week, especially with all the boreal owl and great gray owl sightings that have been happening. That winter, hundreds of great gray owls were spotted in Northern Minnesota by avid birders (there's one report of a birder seeing 226 in a single day!). The Minnesota Ornithological Union predicted that at least 5,225 great gray owls made their way into Minnesota that year. For comparison, the previous winter, they predicted 35 total great grays.
In Minnesota, irruptions of the northern, boreal owl species (specifically great gray owls, boreal owls, snowy owls, and Northern hawk owls) happen regularly. Snowy owl irruptions have been recorded as far back as 1833, and have been identified as happening every 3-5 years since. Irruptions are fairly unpredictable, though. Some years, only one species of owl may irrupt, while other years may see all four boreal species making their way south.
Irruptions are not related to any migratory patterns. Instead, it has to do with the owls' food source. Snowy owls in the north feed primarily on brown and collared lemmings; the others eat mostly red-backed and meadow voles. In all cases, these are small mammal species that go through regular "boom-and-bust" population cycles, meaning that, for whatever reason, sometimes there are TONS of them and other times there are NONE of them (scientists have not yet come up with a logical explanation for why these cycles happen). When there's lots of food, the owls can eat plenty and put more energy into making baby owls. The owl population increases, but sooner or later, their food source will enter the "bust" phase of its population cycle. When this happens, there isn't enough food for the entire owl population to stay north, so they have to start wandering south, sometimes in massive numbers, to find food for the winter. Luckily, most find a good food source; irruption years do not regularly find higher levels of mortality in the owl populations.
This year, we are experience a boreal owl irruption. A recent article in the Duluth New Tribune (http://www.duluthnewstribune.com/event/article/id/258144/) made me realize just how big of a deal this is. Boreal owls are rare species, one that many birders across the country long to add to their life list. Because of this, people have been flying from as far away as Virginia and California for the sole purpose of seeing a boreal owl and adding it to their life list. How lucky that I was able to see one without any effort right at my workplace!
And in this past week, four different great gray owl sightings have been reported in our area, many more than usual. Could the great gray owls be experiencing a minor irruption as well? Maybe they are relying on a food source similar to the irrupting boreal owls? All I know is that there are a lot of owls around and I'm so excited that I've been able to get out and see them.
Last night, Sara (yet another of the first year naturalists) and I went back to county road 11 to see if the great gray owl was still there. Sure enough, right where we left it the day before, it was perched right out in the open. This time, though, as we watched, we noticed it was pretty fixated on the ground. And right before our awe-struck eyes, the owl flew down from its perch and landed on a tasty treat. Through the binoculars, we saw a small mammal hanging out of its mouth and it quickly began to munch down its prize. Too cool.
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