the long-winged mouse hunter

In the Minnesota boreal forest around Sax-Zim bog, we finally found and photographed the hawk counterpart of the Great Gray Owl (from the last post). Rough-legged Hawks are also mouse specialists, but use a completely different strategy to hunt their prey compared to the owls. Where the owls use auditory cues to localize mice under the snow, these particular hawks use visual ones, even honing in on urine trails of voles, which reflect UV light the hawks can detect. Then they perch, sit and wait, and pounce when movements in the snow indicate mouse (in this case, vole) activity.

We weren’t quite sure what we were seeing early in the morning along the roadside as we drove into the bog area. From a distance in the dim light, the hawk first resembled a juvenile Bald Eagle, then the black and white facial pattern resembled an Osprey, which would have been well out of its range for this time of year. Finally, up close we saw the typical mottled plumage of the Rough-legged Hawk.

Rough-legged Hawks are the most northerly breeding Buteo (broad-winged) hawks in North America, setting up breeding territories in the far northern Canadian and Alaskan tundra areas to prey almost exclusively on lemmings there. But they leave the tundra and migrate south to boreal areas of southern Canada and the northern U.S. that have lots of marsh and prairie expanse where they can hunt for voles and other mice where there is less snow cover.

Their name might imply that they have rough scales on their legs, but it is quite the opposite. They are one of three raptors with entirely feathered legs, like owls have — insulation that is invaluable for birds hunting in extreme cold climates like northern Minnesota. This bird, from the carolinabirds.org website (photographed by Dick Daniels) is a captive, tethered with falconry jesses, but its raised wings allow you to see the heavily feathered legs.

Rough-legged Hawks have very long wings for their body size (up to 60 inches in a large, 3.5 pound female) and they are adept at soaring effortlessly over long distances to hunt for mouse activity. Winter birds on a foraging territory in Idaho had home ranges of up to 200 square miles that they traversed over the course of several days of hunting. Researchers estimated that the bird could sustain itself in the winter on a diet of about 5 mice per day. On days when hunting success was limited, the hawks did much more perching than flying, conserving energy for the next day’s hunting attempts.

Long wings give the Rough-legged Hawk a great advantage in soaring, and just cruising over the landscape looking down for potential prey. Although their diet in the summer is largely small rodents, they might prey on rabbits or grouse when they find them in the winter. (Illustration from the Crossley ID Guide to Raptors, on Wikimedia Commons)

I won’t forget this bird — we’ve made four trips to Sax-Zim bog to see it, and finally found one right next to the road, rather than sitting a 1/2 mile away or flying hundreds of feet over our heads. Its striking plumage, feathered feet, and black and white wing patterns should make it easy to ID in the future.

Boreal birds

The Boreal Forest (also known as the taiga) is a harsh place, dominated by snowy landscapes, primarily coniferous trees, extremely cold and long winters and short-lasting, cool summers, but it is the largest land biome circling the high northern latitudes of the globe. In North America that includes most of inland Canada and Alaska.

Boreal forests are dominated by conifers, and usually have an understory of moss or lichen. The coniferous forests of northern Minnesota aren’t really part of the boreal biome, being warmer year round and having many fruit- and seed-bearing plants in the understory. This is an important difference for boreal-dwelling birds.

Over 300 species of birds breed in the boreal biome during its short summers with almost continuous daylight and abundant supply of insects, but only about 30 bird species stay for the rest of the year. In years when food resources are scarce during the winter, some boreal-dwelling bird species “irrupt” and make short migrations south to the northern coniferous forests in Minnesota and other parts of the U.S. These irruptions are irregular both in timing and location, but we can usually find a few boreal species in the spruce-tamarack forest of Sax-Zim bog.

Boreal Chickadees are one of the species that may desert their boreal habitat in search of food in coniferous forests further south. Some years they are never seen during the winter at Sax-Zim bog in northcentral MN, and some years they can be found in abundance. This year, there seemed to be just one Boreal Chickadee hanging out at this particular feeder.

Boreal Chickadees look very similar to our familiar Black-capped Chickadees, but they have a brown cap, gray cheeks, and rustier sides, and their calls are distinctly different. Besides being geographically separated by occurring further north than the Black-caps, Boreal Chickadees prefer to spend their time at foraging at the top of spruce trees, while chickadees forage much lower and in a variety of conifer or deciduous trees. However, their ranges do overlap in the boreal forest, and there is at least one report of a hybrid produced by interbreeding of the two species.

Pine Grosbeaks breed in the farthest northern reaches of the boreal biome across northern Canada, but may retreat to the southern parts of the biome and northern coniferous forests in MN for the winter where they dine on a variety of seeds from feeders and from the understory vegetation of the forest.

These large-bodied, colorful finches are entirely vegetarian: they crush large seeds and fruits in their bills or may nip the tips of the needles off pines or firs. The birds vary in color and even in size throughout their range, which extends around the globe in the boreal biome. Males are pink to rosy red in color and the females have variable amounts of copper color on the head and breast.

Evening Grosbeaks are another large-bodied finch that breeds in the boreal region, and like Pine Grosbeaks, they retreat south during the winter, often in large flocks. Their irruptive movements during the winter are unpredictable and irregular, and they might be found as far south as Texas.

Evening Grosbeaks consume seed in the winter, but are ferocious consumers of insects in the summer, especially spruce budworm. Males in their bright black and yellow plumage really stand out in the gray winter landscape. Females sort of resemble the smaller Goldfinch females with their black and white wing feathers.

Canada Jays (well named because they are found almost entirely in just Canada, unlike the Canada Goose!) stay in their boreal homes year-round, tolerating whatever the climate throws at them. They are well-adapted to the cold, with dense plumage, short beaks, and even feathers that insulate their nostrils!

The best way for Canada Jays to survive the boreal climate is to eat whatever they can find: berries, insects, small mammals, nestlings of and sometimes adult small birds like chickadees, carrion, even fungi. Like some other coniferous forest residents, they store food year-round securing it under bark and in crevices with their sticky saliva. Canada Jays adapt to human presence easily, making use of their food stores (like a hanging deer carcass) and inspiring colloquial names like “camp-robber” and “whiskey-jack”. Do they really sample the alcohol?

Other notable “irruptive” species one might find in the northern coniferous forests of MN like the White-winged or Red Crossbills, Bohemian Waxwings, Red-breasted Nuthatches, Purple Finches, Common or Hoary Redpolls, Pine Siskins, as well as Snowy Owls and Great Gray Owls, all make winter excursions “up north” an exciting adventure in bird watching.

northern bogs and forests

What a great diversity of habitats we encountered on our extended field trip to the northern reaches of Minnesota this past weekend.  One of the first stops just north of Virginia, MN, was the Laurentian Divide, which I had never heard of.  This modest rise of granite divides two watersheds:  north of the divide rivers empty into Hudson Bay and the Arctic Ocean, while south of the divide, rivers drain into the Atlantic, either via the Mississippi River or the Great Lakes and St. Lawrence River.

I am standing on the Laurentian Divide that runs through the middle of North Dakota, northeastern MN, and most of southeastern Canada.  This exposed granite was scoured clean of vegetation by past glaciation, and today is covered by thin soil and sparse vegetation. 

The granite of the Laurentian Divide is part of a huge formation called the Canadian Shield that comprises the ancient core of the North American plate and today underlies most of Canada and part of the northeastern U.S.  The exposed rock was formed approximately 2.7 billion years ago! during a series of volcanic events that resulted in upheaval of a vast area of rock that may have reached 39,000 feet elevation (12,000 m), but is largely eroded to modest hills today.

This boreal forest area of Minnesota is a composite of granite knobs, forested slopes, and boggy lowlands, each with their unique fauna and flora.  In places where the land flattens out over river flood plains, there are expansive grassland hayfields, suitable only for grazing it seems.

Pale Corydalis colonized the barest, rockiest, driest areas of the granite knobs.

The flower reminds me a little of bleeding heart, but it is not in the same family.

A mixed deciduous-coniferous forest typical of northeastern Minnesota. Birch, apen, maple, and basswood are interspersed with red and white pines, and a dense fern understory.

Ground Pine (not a miniature pine but a Lycopodium species) was common in some places. The spores of the brown spikes at the top of the plant are harvested for a variety of uses, one of which is the flash powder used by magicians.

In the low areas at the base of the hills, black spruce and tamarack are the dominant species found in the bogs.  Oxeye Daisys were one of the most common colonists of bare areas on granitic slopes.

Gray Jays replace Blue Jays in the mixed forest.  They are smaller and much quieter than their jay cousins, but just as curious.  They are resident year-round here, managing to eke out an existence and even raise their chicks during mid-winter when temperatures are coldest.  They store food in the summer in sticky balls plastered to the vegetation for later consumption, and may eat anything from fruits and insects to small animals.

Lots of Showy Lady’s Slipper orchids were blooming in the understory, along roadsides, and even in open, wetter areas.

A hummingbird clearwing moth sipped nectar at the honeysuckle flowers.  Swallowtail and Pearl Crescent butterflies also visited this plant along with the moth.  I saw many more butterflies in the northern mixed forest than I have seen in my own garden.

Water percolates through this boggy landscape in channels. You would get really wet feet trying to walk through this area, which is why fur trappers moved their cargo primarily during the winter across the snow instead.

There is much to see in this northern boreal forest, but hikes are not really a pleasant experience right now with all the mosquitoes and flies that attack bare skin.  Maybe that’s why the warblers like it here — lots of flies to eat.

Duck bonanza – round 2

It seems you don’t get lucky being in the right place at the right time twice (on successive days, anyway).  The shoreline was quiet on Vadnais lake yesterday because all the ducks were out in the middle of the lake, even though I was the only hiker around (I think).  Waiting behind shrubbery next to the shore didn’t fool them either; none approached any closer than 500 feet away. Mixed in among the Ring-necked Ducks was an assortment of Common Goldeneye, Hooded Mergansers, and Mallards.

The Mergansers seemed to be floating around in pairs or couples of pairs, while the Ring-necked Ducks were a large floating mob of males (see previous post, Nov. 16).

Hooded Merganser males really are striking birds, with that white crest on the back of their heads, and the black and white stripes on their shoulders and wings.  I wish I could have photographed them closer to me, and with the light coming from the other side, so I’ll substitute the photo from Wikipedia.

The female can erect her head feathers in a similar crest, but it is a brownish one instead.  The photo of the two females below illustrates how different the head shape can look depending on what feathers are flat or erect.  One female looks like she lost the top of her head.

These small diving ducks are very short-distant migrants, moving south from their breeding areas in southern Canada and the U.S. to any open water where they forage for aquatic insects, crayfish, and small fish.  Like Wood Ducks, they prefer to nest in tree cavities, and may even use old Wood Duck nests.  Chicks then have to launch themselves out of the nest, which might be 70 feet above the ground, to follow their mom to the nearest pond.

A recent “Duckumentary” on PBS Nature has wonderful video footage of this behavior in Wood Ducks.

Small, tightly-grouped flocks of Common Goldeneye on Vadnais lake kept far away from shore in the middle of the lake, and also separated themselves from the multitudes of Ring-necked Ducks and Mergansers.

The video below provides a better look at the differences in plumage between males and females and the courtship behavior of the male — a maneuver that looks like he is trying to relieve a neck cramp!  (Scroll ahead to at least to 0:54 where there is a better close-up image of the ducks.)

Like Mergansers, Goldeneyes dive to find aquatic insects, crustaceans and molluscs to feed upon.  They are also a tree-nesting species, but will use the cavities created by broken limbs, and that makes them vulnerable to both nest predation and parasitism (eggs laid in their nest by other species).  Birders in Scotland have put up nest boxes to attract Goldeneyes, which has helped expand the population of these ducks in Europe.

These ducks breed in northern boreal forest (taiga), primarily swampy coniferous areas, all across Canada, Scandinavia and Russia, but, in North America, migrate south to open lakes and ocean shore throughout the U.S. during the winter.  They were a common bird I saw along the California coast in the winter.