Thursday, December 5, 2013

Snowy Owl Irruptions

My Snowy Owl this Thanksgiving. (Delaware Beach State Park)
This past week has been a whirlwind introduction for me on birding the east coast. Having just moved to Delaware, I wasn't sure the places to bird, much less what I could see. Imagine my surprise when I happen to arrive in the middle of a Snowy Owl irruption. This year alone there have already been 6 different snowy owls reported in Delaware! Every state on the East Coast is reporting them and bird watchers and children alike are reveling in this experience.

But what exactly is going on and what can we expect for the future?

First things first, what is an irruption?

An irruption refers to an erratic movement of a particular species/group outside of it's normal range. In the bird world these are generally focused on finches and owls in winter. What causes an irruption can vary based on the species. Finches irrupt as they move south in search of food, this usually happens when fall seed production from coniferous trees turns out lower than expected. This can be due to bad weather in the spring and drought.

Finch irruptions are regularly forecasted by Ontario Field Ornithologist Ron Pittaway. He publishes an excellent report every year on conifer seed production and the expected irruption for finches. Common irruptive finch species include Red Crossbills, Evening Grosbeaks, Pine Grosbeaks, and Purple Finches

Owls will irrupt following a good productivity year in spring. When food abundance is high, owls will hatch higher amounts of owlets. Some pairs will forgo breeding all together! Conversely, a lack of food on the breeding grounds can force an irruption in winter. As temperatures begin to fall starving owls are forced southward to find food.

Snowy Owl's are the main owl prone to irruptions. This species boreal lifestyle depends primarily on the population of lemmings in the arctic. As a result, they irrupt depending mainly on the timing and population of lemmings.

Our last major Snowy Owl irruption occurred in the winter of 2011-2012. Snowy owls were seen all the way from Georgia, Texas, and even Hawaii! While this turned into the biggest irruption in many years, it pales in comparison to some reports from the last 100 years.
(You can read more about the 2011-12 irruption as well as the historical reports here)
What about this year? How does it compare and what can we look forward to?

We have just begun in this current years irruption. One week ago (Nov 23-24), a few Snowy Owls had been reported from New Jersey, Massachusetts, and Maryland, but quickly disappeared the following days. This weekend (Nov 29-Dec 1) birders out on their annual Thanksgiving weekend birding trips witnessed the bloom as dozens of reports came in from Ohio, to Delaware, and all the way down in North Carolina. Currently as I sit here writing this (December 1st) there are even reports all the way in southern Illinois and Bermuda! Clearly they're moving south.

Lets look at how this irruption compares to the one in 2011-2012:
Ebird Snowy Owl reports from the early winter months in 2011 (Oct-Nov)
In 2011 Snowy Owls began appearing along the east coast, but the main population exploded down the great plains. Every plains state had reported a Snowy Owl before the end of November.

This year looks a little different:
Ebird Snowy Owl reports for this current winter (Oct-Dec 5)
We see much less movement down the central United States this year, with a higher concentration along the east coast. We notice the southern expansion along the eastern United States is already more mature than two years ago.

As we're just beginning this great year for Snowy Owl's we can look ahead at whats to come:
Ebird Snowy Owl reports from 2011-2012 during the entire winter (Oct-Feb)
In 2011-2012, the Plains states received almost unheard of numbers of owls. Kansas and Missouri shattered their previous records with total counts as high as 101 and 54 respectively. South Dakota, the center for that years irruption, had one report of 20 snowy owls over a 40 mile stretch!

As far as this year is concerned it seems the irruption is centered around the eastern United States, with the Great Lakes regions reporting the highest numbers in the US. If this irruption continues through the winter, I'd expect birds to follow the east coast and Mississippi river southward, hopefully overshooting the Ozarks into the great plains.

We'll see how it turns out, but regardless it's already been a lot of fun.
So we know they could be showing up anywhere this year, but where should we look?

Two Snowy's perching on the sand dunes in Delaware
Snowy Owls live on the flat arctic tundra, because of this they prefer flat areas that are generally raised and light in color.  I would search any areas where the ground is lighter and open such as fields, prairies, and of course sand dunes. Their bright color can be unmistakeable, so feel free to drive around back roads looking for them.

That's all for now! Bird safe and don't harass the owls!

And if you see one don't forget to report it on Ebird and your local bird forum. Scientists and birders alike will thank you!


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