by Hunter Hebenstreit

Every few years or so, the Lower 48 experiences an invasion of arctic visitors. After spending the summers breeding on the Arctic Tundra, Snowy Owls have two options: spend the winter in the perpetual darkness of the north, or head south. Every several winters, Snowy Owls head further south than usual, and in much greater numbers. This is known as an irruption. There are many misconceptions as to why this happens, as well as many theories.

The biggest misconception about irruptions is that they are caused by a lack of food; that the owls are driven south in search of food. According to Project Snowstorm, an organization that bands and tracks Snowy Owls, they are caused by the exact opposite. During summers in which prey is incredibly abundant on the breeding grounds, owls produce larger clutches (8-9 instead of 3-4) and chicks fledge with more success. Then come winter, thousands of those young owls head further south than usual. According to researchers, owls in irruption years are often heavier and healthier than those in non-irruption years.

Last fall, researchers were already able to predict that this past winter would be an irruption. There were several signs on the breeding grounds, including a boom in lemming populations as well as more young owls than usual sighted by caribou researchers on the tundra. It turns out they were right. The lower 48 saw much higher Snowy Owl numbers than usual. The following map from eBird shows all of the reported Snowy Owl sightings from November to March of 2017-18. Owls have been seen all the way to Texas, with hundreds of sightings throughout the northeast and midwest.

While it is true that Snowy Owls in the south may not be starving, they still face dangers of many kinds. They are more likely to come in contact with cars, airplanes, rat poisons, or other human-caused dangers. These owls are not used to human contact, and will often let humans get very close. We as birders have the responsibility to not make these creatures’ lives any more difficult than they already are by giving them their space and practicing ethical birding methods.

Irruptions cause much excitement among birders, many of whom will have a chance to see a beautiful species they normal would never encounter. Understanding how these irruptions work brings us one step closer to understanding the minds of one of the most majestic arctic predators.