Listening for Owls

My latest owl sighting, another great gray owl on Highway 6 on March 10; although, all credit for spotting this relatively small guy goes to my sister, Katy, who was up visiting with my mom for the weekend. 

On Thursday, I drove out to Isabella and met up with a birder named Steve, a retired forest service and DNR employee. For the past 20+ years, he has been conducting owl surveys in Isabella and I wanted to join him for a night to see what the process was like and maybe begin similar survey work at Wolf Ridge. The survey is conducted by listening for owls.

Owls are the most vocally-inclined family of raptors, some species producing more than a dozen different types of calls. The most prominent of these calls is the male's advertisement, used to proclaim ownership of a given territory. In addition to territoriality, various owl calls are used when owls are indicating fright, threatening an enemy, summoning a partner, begging for food, preening a mate, copulating, or transferring prey. The calls are unique to each species; in fact, it was the difference in calls that caused ornithologists to recognize the Eastern and Western screech owls as two separate species in 1983.



In addition to the varying calls of the different species, each individual owl has a uniquely recognizable voice. Researchers have recently started to use sonogram technology to identify different owl individuals, which opens up tons of research possibilities; for example, some researchers are now studying lifespan and length of territory occupancy in barred owl individuals.

Captive male barred owl at the Raptor Center in St. Paul, November 2012

Most owls sing at night, beginning around dusk. It had just gotten dark when Steve and I reached the beginning of the route we were planning to survey. We got out of the car and silently listened for three minutes for the sounds of any owl calls. Hearing none, we got back into the car, drove about 3/4 of a mile, got out and listened for three more minutes. This distance is determined by the fact that the quietest owl calls, those of the Northern saw-whet owls, can only carry 3/4 of a mile in good conditions; conversely, great-horned owl calls can be heard up to three miles away. This was the basic process, and this is what we did for the next four hours. It was certainly tough at times, mind-numbingly repetitive. Also cold. But at least it was a beautifully clear night and I was able to do some star-gazing to compensate for the complete silence of the owls.

Steve was surprised that we didn't hear any owls. The owl calling usually begins around the middle of March and will persist through May. Some owls will continue to sing even as they are incubating eggs, and occasionally even after the chicks have been born. On the other end of the spectrum, boreal owls will cease singing as soon as they find a mate. Steve was particularly hoping to hear some boreal owls during our survey (theoretically, there should be more around than usual because of the irruption); if we had heard one, we would have strapped on some snowshoes and gone searching for its nest, as it might be the only time that owl advertises its location vocally. In fact, Steve was so excited about hearing a boreal owl that we ended up driving more than ten miles down an unplowed road to a location where a resident pair has nested for many years. At one point, we had to shovel his truck out of a snowbank, and still heard nothing to reward our efforts.

Boreal owl seen at the Kohlstedt family bird feeder, early February 2013 (photo: John Kohlstedt)

Despite our coming up empty, I know we'll start hearing owls eventually. Owls are famous for being noisy and persistent. One Swedish great gray owl was recorded for four hours every night, repeating his hooting sequence no less than 310 times. A Western screech owl in Washington was recorded calling for two hours straight every night (at 8 calls a minute, that's 960 calls a night!) Boreal owls in the Western U.S. typically call for 2-3 hours straight, rarely pausing in between. Owl calls are also infectious: it isn't uncommon to hear multiple species calling in the same area. There are even five species in which the male and female are known to sing duets together.

Since Thursday night, I've done a little bit of listening at Wolf Ridge (and also amplifying different calls  from my iPod to see if that triggers a response). Still nothing, but I'm hopeful that as the weather warms and spring quickly approaches, it won't be long before I'm listening to the calls of the owls every night.

Owls Everywhere!

On Tuesday, I joined my favorite engaged naturalist couple Anne and Tom for a brief birding excursion. We'd heard that at this time of year, great gray owls are frequently seen on Forest Road 11. There had been multiple reports of great gray owls being spotted in this area in the past week, so we thought it was worth a try. We drove slowly, just before sunset, looking in all the trees for that distinctive owl shape. Sure enough, after about four miles, perched right out in the open, we found what we were looking for - an AMAZING bird. We observed and photographed this owl for probably 20 minutes, hardly able to contain our excitement.

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.

Wolf Ridge's Mystery Owl

A small owl of boreal and montane forests, the Boreal Owl is found throughout Alaska and Canada, and across northern Eurasia, as well. It is found in the lower 48 states only in the mountains of the West, in extreme northern Minnesota, and as an occasional winter visitor to the northern states.

I was doing a bird banding presentation for a class yesterday morning. I started it as I always do, by asking the kids what birds they'd seen today. One girl started listing the usual cast of characters: "black-capped chickadees, red-breasted nuthatches, common redpolls, a hawk owl, downy woodpeckers..."

"Hang on just a second there," I cut her off. "Did you say hawk owl?" Their naturalist, Robyn, nodded and smiled. I thought that maybe the kids had thought they'd seen a Northern hawk owl and Robyn was letting them enjoy that rather than correcting them. But they all insisted, and when Joe (a significantly experienced naturalist evaluating the class at the time) also confirmed the sighting, I found myself stumbling for words, until I finally sputtered something like, "you saw an owl and didn't come and get me?!"

Small owl; no ear tufts; white face outlined in black; fine spots on top of head; underparts dirty white, streaked with brown; bill yellow.

After teaching her class about bird banding, I booked it back to my office to grab a camera and took off for Chickadee Landing, the location of the owl sighting. With five or six other naturalists in tow, we started scanning the trees for the little ball of fluff allegedly perched above us. We scanned the area for about fifteen minutes, and I even tried playing some hawk owl calls on my iphone, but to no avail.

Lives in boreal forests with spruce, aspen, poplar, birch, and balsam fir. In mountains of West, found in subalpine forests of fir and spruce.

At lunch, I learned from Robyn that our owl was not perched out in the open, as I had originally thought, but rather, tucked back into the branches of a spruce tree. She offered to take Tessa, Dan (more WR nats) and me back out to look for the little guy one more time. And thank goodness we returned, because as soon as we arrived, "oh sure, he's right where I left him," Robyn declared.

Diet: small mammals, birds, and insects.

Sure enough, tucked into the branches of a spruce tree sat a very passive owl. Clearly content with just hanging out, it would occasionally look our way, especially as we got closer, but otherwise, seemed entirely unperturbed by our presence. In fact, we were probably the least of its concerns, given the many black-capped chickadees noisily flitting about in its tree. We really hoped this owl might take an opportunity to make a meal out of one of them, but instead, it continued to sit. This is normal behavior for owls during the day - quietly hanging out and minding their own business.

Boreal owls usually are considered monogamous, with one male mating with one female. Several studies in Europe found that one male may mate with up to three females, and a female occasionally mates with two different males. They found that such multiple mating occurs most frequently when mice numbers are at their highest. (Finding easy prey to feed the young means that less help is needed in raising young owls.) When mice numbers are low, all the owls were monogamous.

When we first saw the owl, we instinctively found ourselves questioning its original identification as a hawk owl. I suggested that maybe it was a boreal, but we immediately brushed off that suggestion given the size; this owl looked much bigger than the boreal owls we'd seen in captivity or taxidermied. Plus, the other naturalists had already identified it as a Northern hawk owl - why question that? However, last night when I posted a picture and blog entry about the owl sighting labeled as a Northern hawk owl, I almost immediately got a phone call from my raptor banding mentor at Hawk Ridge, Frank, informing me that the image was definitely a boreal owl. And that makes sense. The tail is short and rounded, there is no horizontal barring on the front, and this is an irruption year for boreal owls, meaning that they are being spotted all over the place in northern Minnesota (I'll write more about this in a future blog entry). This particular boreal owl just so happened to be quite large. Or maybe it was just a female.

The female boreal owl is much larger than the male. The species shows the most extreme reversed sexual dimorphism (the phenomenon in the raptor world where the female is larger than the male) of any American owl.

"It makes you wonder how often we miss these kinds of things," Tessa mused, as we watched the owl peacefully perched in its tree. We would not have noticed this owl if Robyn hadn't taken us back out and pointed its exact location. How many other awesome plants and animals are we missing every single time we go outside because of their passive, reclusive nature and our inability to catch every detail?

(Field guide notes from:  http://www.allaboutbirds.org/guide/Boreal_Owl/id)