A Minnesota birder recounts the recent, unexpected abundance of three nocturnal birds of prey.

by Sharon Stiteler

About the author Sharon Stiteler, aka BirdChick, manages a wildbird specialty store in Wayzata, Minn.; maintains a website at www.birdchick.com; and serves as the local birding expert for television station KARE11 and radio station 107.1 FM.

Traditionally, Minnesota is known as a great spot for seeing northern owl species during winter. Birders come from all over the country to Sax Zim Bog in St. Louis County to see Great Gray Owls, Northern Hawk Owls and, in really good years, a Boreal Owl. In the winter of 2004-2005, something went weird.

Birders in the North Star State participate in two online listservs, mou-net and MnBirdnet, and reports of owls on the listservs started in August. No one paid too close attention; the state has a few resident pairs, and reports in late summer and early fall are usually those birds. Birders enjoyed the fall hawk migration and a wayward Clark's Nutcracker through September. Then, as an afterthought to a previous post, Earl Orf reported, "I forgot to add this to my North Shore Birding post from yesterday. On the way home from Duluth, Shawn Conrad and I went through Sax Zim and saw two Great Gray Owls."

Momentum in October

Not long after that, Northern Hawk Owls were reported in the bog. Local bird guide Mike Hendrickson had given directions to a birder to find Great Grays at Sax Zim, and they found hawk owls instead. Before long, others were reporting different hawk owls in different locations around the bog. Early reports from owl banders predicted an owl irruption and the possibility of a good Boreal Owl year.

By the end of October, at least seven Northern Hawk Owls were seen in Sax Zim Bog, and an eighth was observed at Stoney Pointe in Duluth. A few Great Gray Owls were observed but were outnumbered by the hawk owls.

In early November, birders began seeing three Great Gray Owls in a day at Sax Zim Bog. As the month went on, reports of Great Grays came from Grand Marais, Duluth and Aitkin County. It was official: An irruption year was underway.

Because irruptions—the periodic movements of numbers of birds into unusual ranges for a season—can be unpredictable and many birds die off, birders began heading north to see how many owls they could find in a day. In early November, that number was three to four Great Gray Owls. By the end of November, the tally ranged from 22 to 27 Great Grays, and it didn't stop there. Mark Martell of Minnesota Audubon exclaimed, "My gosh, I just realized that I have seen more Great Gray Owls in one day than I have in my whole life!"

As if the volume of owls wasn't incredible enough, unusual color variations of Great Gray Owls also appeared. In November and December, birders documented albinistic Great Grays in St. Louis County. In late November, Minnesota Ornithologist Union president Mark Alt filmed a melanistic Great Gray near the town of Cotton in St. Louis Co. This was particularly exciting because there is no previous documentation in any literature suggesting that Great Grays occur in a dark color morph. Images of both birds can be found at the MOU website.

In Search of Food

The influx of owls last winter likely stems from a food shortage. Dr. James Duncan of Winnipeg, Manitoba, and author of Owls of the World (Firefly Books Ltd., 2003) has studied vole populations since 1986. He noted that the vole populations he studied in 2004 were the lowest since 1992, when Minnesota had its last major irruption. Dr. Duncan speculates that cold, wet weather affected the voles' food sources and subsequent breeding cycle, in turn affecting the northern owls' food source.

In an irruption year, the owls that come down typically are stressed and starving. Many brought into raptor rehabilitation centers are starving to the point that they need to be fed a slurry or have to be euthanized. Almost all of the injured Great Gray and Northern Hawk Owls brought into the University of Minnesota's Raptor Center were injured by collisions with vehicles.

Of the more than 500 Great Gray Owl carcasses collected, some went to the raptor center, and most went to the Chicago Field Museum of Natural History to become study skins for future ornithologists. Great Grays seem particularly susceptible to collision injuries, because they hunt close to roads and even major highways. The owls tend to sit on top of tamarack or spruce trees; when they hear something edible, they drop from their perches and fly low over the ground to the unsuspecting prey. Unfortunately, many owls pay no attention to oncoming traffic, and even the most careful of motorists couldn't help hitting an owl with their vehicle. Most of the Great Gray and Northern Hawk Owls that were found dead or trapped for banding purposes were fat and well-fed.

On the other hand, most of the Boreal Owl carcasses showed that this species was dying off more from starvation than from collision injuries. The deep snow cover that makes for an ideal breeding ground for micotrine moles is no problem for Great Gray or Northern Hawk Owls to penetrate, but it is incredibly difficult for Boreal Owls to hunt through deep snow, which could account for the species' starvation.

Great Numbers

People who live in the area of Sax Zim Bog were just as surprised by the irruption as the birders. Wilbert's Cafe on the northwest corner of the intersection of highways 50 and 52 had a booming winter business. The owner kept a notebook for guests to sign; page after page was filled with names of people from around the country and the world, including Hong Kong.

Information, like birders, keeps flooding in. Peder Svinger of the Minnesota Ornithologists' Union Records Committee, along with researchers Jim Lind and Steve Wilson, have each spent hundreds of hours compiling owl reports. As of late March, reports indicated locations for more than 400 Northern Hawk Owls and 3,750 Great Gray Owls. The reports were behind on Boreal Owls, but a very conservative estimate is more than 450 individuals in the state.

Svengin speculated that many would stay in Minnesota for the breeding season. Nesting records have been few and far between. Svengin revealed that nesting platforms had been placed in undisclosed locations to encourage the owls to nest.

April brought warm temperatures, longer days and, indeed, evidence of breeding northern owls. Birders still could see Great Gray Owls in Aitkin and Pine counties during the spring, but time of day became a consideration because the birds returned to hunting at dawn and dusk. Also, if the owls are nesting, one of the pair would incubate eggs, reducing the number of owls that birders are likely to see.

As of press time, many Great Gray Owls were documented hooting in pairs, but no nests were officially documented. Each year, Minnesota has a couple of Great Gray pairs that nest in Aitkin and St. Louis counties, so there likely will be more this year.

In the past, very few Northern Hawk Owls were proven to nest in the state. The best record was in 2002 when two pairs nested along the Gunflint Trail. This spring, at least six pairs have been documented calling on territory. In March, Mike Danzenbaker found a pair in the Sax Zim Bog area, and in April, Mike Hendrickson took photos of the nest site.

Details about the irruption and its effects on local birding continue to generate excitement and chances to study the birds and their behavior. Stay tuned for more from the North Star State.

This article was first published in the July/August 2005 issue of WildBird.
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