I Saw a Mobbing in Canada

Last weekend, Jill, Sara, and I took a mini-road-trip up to Thunder Bay in Ontario to spend Easter weekend with Jill's boyfriend, Peter, and some of their awesome Canadian friends. The weather was unbelievably terrible, so most of the weekend was spent indoors watching Game of Thrones, or in various Canadian coffee shops, restaurants, or markets playing cards and hanging out.

This is what a Canadian Easter looks like (photo credit: Sara Sloan)

That's okay, though, because we got a huge dose of nature awesomeness during our drive north. Shortly after crossing the border (I successfully managed not to say anything stupid to the border agent), we noticed what is becoming a very familiar sight this year: a great gray owl perched on the road-side telephone wires. That trip marked my fifth and sixth individual great gray owl sightings of the year! Naturally, we pulled to the side of the road to get a better look ("classic facial discs" -Jill). All of the sudden, two ravens came flying out of nowhere, dive-bombing the formerly peaceful owl. The owl immediately flew to a different perch, but the ravens were persistent, flying at the owl no matter where it flew. Eventually, the owl ended up flying down to the ground under the cover of some trees, and the ravens settled down, but remained perched nearby, seemingly ready to pounce should the owl attempt to relocate again.

As surprising an event as this was to witness, I was even more surprised to discover the birds mobbing owls is a fairly common event. Given that owls regularly eat songbirds, the mobbing is a defense mechanism when an unwanted owl is hanging around. Some researchers have managed to incite mobbing behavior in songbirds by simply playing an owl call in their vicinity. Turns out that corvids (ravens and crows) are both the most common mobbing culprits and also the most vicious; the "guarding" behavior that we observed is normal. This is also why one of the names for these groups of birds is a "murder" of crows and an "unkindness" of ravens.

Mobbing potential owl predators offers three benefits for songbirds. First, it will hopefully result in the removal of a harmful predator. Second, it is a way for parent birds to teach offspring which birds are dangerous predators. Third, if young notice this behavior is happening, it will typically act as a warning sign for them that a predator is nearby and they should take appropriate caution.

When songbirds want to initiate a mob, they will give a distinctive call, which acts as a "call to arms," harkening to the other birds in the area to assist in the mobbing. Birds of all sizes have been observed to participate: an Anna's hummingbirds (4.3 grams) was once observed mobbing a spotted owl (1.3 lbs), a 142-fold difference in size (for a comparison, think of a very small child poking an elephant in the leg with a stick). If owls are being mobbed by "harmless" birds, they will often ignore the event, sometimes even sleepily closing their eyes until eventually the mobbers give up.

In a study by Frederick Gehlbach, 60% of mobbings on screech owls happened during the breeding season. This is the time of year when owls are feeding themselves AND fledglings, so the rate of preying is significantly higher. Also, resident and wintering birds were found to initiate a mobbing more frequently than migrants - an owl is a greater threat to a bird that lives near it permanently than one that is simply passing through.

A couple days ago, I hiked up to Caribou Falls, a short one-mile loop of the Superior Hiking Trail. The ice is finally starting to break up and flowing water is beginning to appear again. While watching the half-frozen water fall, I once again saw some ravens ganging up on a dangerous predator, this time an immature bald eagle. Demonstrating very similar behavior to what I saw in Canada, they continued to launch themselves at the eagle until it eventually flew away.

This is what April in Northern Minnesota looks like. 

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.