the prolific and versatile American Robin

American Robins rank third in numbers behind Red-winged Blackbirds and introduced Starlings as the most common bird in North America. To what do they owe their great success, compared to Cardinal and Bluejays, for example?

Note added after posting: Valerie Cunningham who writes a bird column for the Minneapolis Star Tribune uses a more reliable source for estimates of bird populations in the U.S. and Canada. According to the Partners in Flight Database, the American Robin is THE most numerous bird in North America, at an estimated 370,000,000 birds, far outpacing the Red-winged Blackbirds (160,000,000) and Starlings (86,000,000). So that makes what I have said below even more impressive!

An American Robin eyeing the few remaining fruits available at this late date during the winter.

One strategy for being prolific: breeding early and often — producing as many as three clutches of chicks during a breeding season lasting from April to July. Robins are one of the earliest to nest, and continue to raise broods until the flush of insects has diminished in late summer.

Robins consume a lot of invertebrate prey during the spring and summer. Earthworms are a favorite on the menu for their chicks, but they also hunt aquatic invertebrates by the pond’s edge as well as insects hopping through the grass.

Another strategy for being versatile is their flexibility in changing diets as the seasons progress. We think of Robins as being primarily fruit eaters, and they do consume a lot of fruit in fall and winter — indeed, as much as 60% of their diet over the course of a year may be fruit.

Fall is the time to pig out on crabapples.

The fall crop of juniper berries feeds a variety of fruit-loving birds: cedar waxwings, warblers, mockingbirds, robins, even cardinals dine on these nutritious little morsels.

Later in the winter, with most of the chokecherries, hawthorn, dogwood, crabapple, even sumac crops depleted, Robins resort to consuming less palatable buckthorn berries, many of which have dropped off the trees by then.

This dietary switch from eating mostly animal prey to consuming mostly fruit is not trivial. There are major changes in gut anatomy, changes in types of enzymes synthesized for digestion, and amount of food to be consumed and the rate it is moved along the digestive tract daily that must take place during a short transition time of about two weeks. Ask any vegetarian what happens when they try to eat meat and you get a sense of what Robins must deal with twice a year as they switch food sources. So, we must credit their dietary versatility for their ability to survive and become one of the most common birds in North America.

But here’s a new wrinkle in the Robin’s key to success in surviving the food desert of the late winter landscape in northern latitudes — fishing! Recently someone posted photos (on Facebook’s Minnesota Birding site) of Robins fishing for minnows near the edge of a pond free of snow. One or more Robins poked a hole in thin ice, big enough for minnows to find as a place to gulp some oxygen in their severely anoxic swampy pond, and the patient Robin simply pulled them up for a meal.

Now that’s a clever bird! And its success does not go unnoticed. (Photo by Laura Segala.)

Moments later, a bunch of Robins want to try fishing at the hole. (Photo by Laura Segala)

This is not one isolated instance of American Robins eating fish. There are reports in the scientific literature as early as 1954 of Robins feeding on dead shiners, as well as newspaper articles documenting Robins hanging around bait shops for the dead minnows being thrown out.

American Robins are truly versatile and adaptable — and as a result are very successful in populating North America.

Mornings along the creek

Today is two months after the winter solstice (Dec 21), and we now have two more hours of daylight each day (almost 11 hours). More importantly, the sun rises each day 13 degrees higher than it did on the winter solstice (35 vs 22 degrees above the horizon), and it is now more than half way to its maximum altitude in our summer sky on June 21 (68 degrees).

What does this mean for us winter-weary Minnesotans — spring is ever near! Cardinals and Chickadees are singing up a storm on sunny mornings when the radiant heat of the sun can actually be felt through the chilly (20 F) air. The polar vortex is history, and it’s time to get out and enjoy the end of winter, — like taking a morning walk along the Sucker Lake creek.

This creek connection between Vadnais and Sucker lakes is a popular spot for mallards and Trumpeter Swans because the water is open and flowing all year. Unfortunately, there is nothing at all for the waterfowl to eat here because it has been picked clean over the previous months.

A Trumpeter Swan swimming through the ice chandeliers on the creek…

A pair of mallards takes off right in front of me.

At the north end of Sucker Lake, over 100 Trumpeter Swans swim in a small pool of open water near the inlet.

A mixture of adults and juveniles (brown heads) have been congregating here throughout the winter, spending nights and mornings on the water before flying off to forage in agricultural fields. Toward the end of the winter, swans and other wildlife (e.g., deer) spend more time resting and less time actively foraging, since there is very little left to feed on and whatever is there is probably well-covered by snow. By resting more, they expend less energy and conserve their energy reserves.

Morning nap time…

Last year’s offspring (swans with gray-brown heads and necks) remain with their parents through the winter, and perhaps pick up a few good tips on where to find food during this period.

Mom or Dad Swan tried a new place to look for submergent vegetation, and the youngster follows.

Long necks are definitely good for reaching into tight spaces, and this adult must have been finding something because it kept at it for several minutes.

Taking a break from all the morning’s activities…

Just passing by

Every now and then, a red fox runs through the far back of the backyard, usually too quickly to get a photo. But today a red fox trotted right in front of my porch window where I was sitting admiring the snowfall in the backyard…and my camera was close by.

The fox never stopped, just trotted by the window and hopped the fence into the neighbor’s yard. Too much telephoto to get the whole fox in the photo.

A beautiful animal, moving effortlessly through the snow. I have noticed fewer gray squirrels under the bird feeders this winter, so maybe this animal’s presence is the reason.

What’s up with this weather?

We have been in the grip of a prolonged vortex of cold air from our northern neighbors since February 4 with daytime highs in the negative digits (F) and nighttime lows dipping well below -10 F (e.g. last night was -21 F). Just for something to inspire me mentally (?), I added up the last 10 nights of low temperatures and came up with a grand total sum of -95 degrees. Now that’s arctic! Needless to say it’s difficult for my fingers to work camera buttons at these temperatures, let alone get outdoors for a walk in the backyard.

But, in the spirit of Valentine’s Day and to commemorate a time when I was braver about venturing out in -15F weather, here are a few photos of the Trumpeter Swans on the Mississippi River at Monticello, MN, engaging in courtship displays to cement their pair bond — love is in the air for these swans, most of which mate for life.

Even in the warmth of a beautiful sunrise, this landscape looks unforgivingly cold. And it was about -12F on February 9, 2014,

Trumpeter Swans pair up about the age of 3 or 4 years. Each year, there is a lot of “conversation” between members of the pair as they go about their ritual of preparing for the next breeding season.

Head bowing is an important part of the ritual — always done in synchrony.

The iconic heart-shape formed by the arches of their necks as they face each other during a part of the courtship ritual. This shot is always a popular Valentine’s Day image.

The swan pair stay together all year long. In the winter they spend the night on the water, then fly off together in the morning to forage in fields where there might be some left over grain. They will remain together, rearing a clutch of 2-5 or even 6 goslings each year, until one or both of them die — some as long as 25 years.

Some males that have lost their mates never find another female to form a new pair bond with and remain bachelors the rest of their lives. Hiking along a creek on a cold February day in 2016, I found one lone swan accompanied only by Mallards.

Thinking of warmer days ahead, I wish you a Happy Valentine’s Day, 2021.

Baby, it’s really cold out there…

It wouldn’t be winter in Minnesota without a week or two of sub-zero (in F degrees) weather (-2F this morning and that’s -19 degrees C). And the little birds have been hitting the feeders pretty hard lately, especially the peanuts.

Chickadees never seem to slow down, regardless of the weather. But they were slow to get up this morning and didn’t make an appearance in the backyard until the sun was well up.

Now here’s the problem with being a small bird trying to survive in this winter climate. Heat will be lost from a body surface when the body is warmer than the environment, and in the case of the chickadee, whose body temperature is normally about 107 F, that is a 109 degree difference between its internal core and the air temperature hitting its feathers this morning.

In addition to this huge thermal gradient for heat loss, small birds like Chickadees have a very high ratio of surface area to their heat-producing body volume — thus accelerating the rate of heat loss. [If you’re interested in why this is, we can talk about the mathematical basis of surface to volume ratios in the comments…]

The chickadee looks like a sphere at rest, because that’s the shape that conserves heat the best. Maximal fluffing and tucking exposed parts in is essential in these subzero temperatures.

Chickadees are metabolic marvels, being able to harvest enough energy from their foraging efforts all day to last them overnight and part way into the next morning, before they can visit their stash of seeds or a bird feeder. BUT…they are economical with their overnight energy expenditures (because you never know what the next morning’s weather will be like), and they make their fat reserves last by lowering their body temperature as much as 20 degrees F (from daytime highs of 107 F to night-time lows of 86 F).*

Hypothermia makes it possible for Black-capped Chickadees and most other titmice members of the Paridae family to survive winter cold in northern latitudes. Not all birds can or do utilize this strategy. Some species, like Common Redpolls, eat a more fat-rich diet to have a larger overnight energy reserve. Some species, like the Common Bushtits that weigh half as much as a Chickadee, share body heat with each other by roosting together communally, packed tightly side by side on a branch. And some species, like Eastern Bluebirds do a little of both the Chickadee and the Bushtit strategy to make ends meet energetically.

I was intrigued the other day when I found Eastern Bluebirds going in and out of the bluebird boxes at Como Park golf course. I knew they weren’t setting up nest sites at this time of year, so they must be taking refuge from the cold in the boxes. It’s unusual for these Bluebirds to stay this far north in the winter, and I wondered how they were managing it.

Multiple birds in the same box together would be ideal for conserving some body heat on a cold day, in the same way we use the shelters at the bus stop and (used to) stand close to friends and family to retain heat.

Groups of six to eight Eastern Bluebirds in Indiana were observed to roost together in a nest box overnight, forming a circle with their heads toward the center of the box and pointed downward below their bodies so the heat from their exhaled breaths was directed toward the other birds.** It’s possible they might be using this heat conservation strategy during the daytime as well here in Minnesota, when multiple birds enter the same box.

In addition, Eastern Bluebirds forage in small flocks during the winter, using the strategy of more eyes to find food. And when they take a break from foraging intensively, they often huddle tightly together on a branch close to the trunk of a large tree that provides some protection from heat loss from the wind.

Scott Mohn found just such a collection of male Eastern Bluebirds huddling together on a tree limb at Como Park golf course on this cold morning and graciously allowed me to use his image. (Click on the image to see it full screen). Notice these are all male bluebirds, which would not tolerate each other’s presence during the breeding season. But for the purpose of winter survival, they are bosom buddies.

It must be tough to be an Eastern Bluebird that depends on a fruit and insect diet to find enough to sustain itself overnight in Minnesota’s subzero climate. What do they do if they can’t find sufficient food to last them overnight? Bluebirds in Indiana were lethargic and immobile when researchers opened the nest box after a cold night; it’s possible they might also be lowering their body temperatures overnight to conserve energy like the Chickadees do. But there are no published data on this — at least that I can find.

*The data on hypothermia in Chickadees overnight was part of my Ph.D. thesis at Cornell University in 1973.
**The data on communal roosts of Eastern Bluebirds in Indiana was published by Frazier and Nolan in 1959 in Bird Banding.

Winter Blues

As in blue sky (for a change) and Bluebirds (that shouldn’t be here at this time of year) on a sunny day with an unseasonably high temperature hovering near freezing (30 F). For a change of pace I went walking on the local golf course, curious to see whether I could find the reputed Mountain Bluebird that has taken up residence here along with aforementioned Eastern Bluebirds.

But I found only the eastern cousins, near two Bluebird boxes, which the birds were sitting on and inside of during the middle of the day.

A small flock of about 6 male Eastern Bluebirds flitted between the nest boxes and the shrubby woods on one side of a cross-country ski trail. Periodically, they dipped into the boxes or peered into the hole. I suppose they might take communal refuge from really cold weather in these boxes, but I was surprised to find them doing this on such an unseasonably warm(?) day.

Although Eastern Bluebirds breed here in the summer, they usually retreat south in the winter to places that have less snow cover and milder temperatures where they feed on a wide variety of shrub and tree berries and mealworms provided by friendly birdwatchers. What a treat to see their cheerful bright blue and rusty brown colors on a landscape that is mostly white, gray, and brown this time of year.

The landscape at the Como Park golf course is mostly white on white, with only an occasional tree to break up the monotony. But cross-country skiers love the rolling hills and groomed trails here. And bubblers keep one pond unfrozen so birds can find fresh water when they need it.

Two males, perhaps different in age or fitness, as the amount of blue on the head and back indicates maturity and signals health and vitality of the individual.

Good luck, little Bluebird. You are about to face a week of single digit and subzero temperatures — I hope you’re prepared for that.

Squirrels on notice!

There are not one, but two mammalian predators looking for the squirrels in my backyard. One of the red foxes stopped by the other day, furtively sneaking along the fence line between backyards, pausing under some evergreens for a look at the bird feeders, and then hiding next to a shed in my neighbor’s yard.

The squirrels were smart enough to avoid this red fox, an infrequent visitor to my backyard this winter.

But the next day, a coyote lingered in the backyard, hunting along the edge between the grass and the forest for unsuspecting squirrels.

This particular coyote had a foxy-looking face, and some reddish fur on its head and ears, so I was confused at first glance. But it was noticeably bigger than a fox.

The head doesn’t look quite right for a coyote, but the body fur is definitely not fox. This animal was also smaller and less husky than the coyote that visited several years ago.

Coyote in the backyard, December 15, 2013. Usually coyotes will displace red foxes from an area, either by intimidation or by attacking and killing them. So I’ll have to see which one sticks around for the rest of the winter.

White on white

They are hard to see against a backdrop of fresh snow, except for the large, dark black eyes, and the black tip at the end of their tail.

Meet Herman, the ermine, who is in the winter fur phase. Herman had just been feeding on part of a carcass left out for the overwintering birds at Sax-Zim bog, and the tip of his nose is bright red from the bloody meat. This little Short-tailed Weasel has been hanging out at the Visitor Center for several days, and shows up regularly every morning (and evening) for a snack.

It’s a cold day to be running around on the snow, and these ferocious little predators have huge appetites to keep their metabolic furnaces going. They need to consume about 30% of their body weight daily. Deer carcasses are for weasels what bird feeders are to our feathered friends — a ready source of rich nutrients in times of need.

The long, thin bodies of weasels are a great adaptation for hunting rodents in their burrows, but they are a disadvantage in the winter climate because thin cylindrical bodies lose heat much faster than more spherical-shaped ones do.

Weasels are excellent climbers, so this part of the carcass hung in a tree is no problem for Herman to get to. Time for a little fat to add to the meaty part of the meal consumed earlier.

Weasels usually retreat to a burrow, perhaps of some animal they have recently eaten, when they are not active, and they will often cache extra food there to tide them over on days when prey are scarce.

This is what Herman looked like last summer — but molting the summer hair to all white coat in the winter serves two purposes: being less conspicuous to prey they are stalking, and being less visible to predators that focus on the black tip of the tail instead of the head of the animal that is white on white against the snow.

What determines when weasels molt into their white fur? It’s thought that declining hours of daylight in the fall are the primary cue, just as it is for migratory birds to begin their preparation to fly south. Molting from brown to white fur coat takes about three weeks, but a drop in temperature can hasten the molt, and unseasonably warm fall weather can slow it. Usually the molt to the all-white ermine phase is completed just about the time of the first snowfall, so the animal is perfectly camouflaged.

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.

the Great Gray

A trip to the land of gray skies, little light, dense spruce and tamarack bogs, and chilly temperatures in north central Minnesota gave us an opportunity to see one of the most iconic animals of the northern Boreal forest, the Great Gray Owl, in action, doing what it does best — hunting mice under the snow.

[Note added after posting: if you’re interested, read the comments below the post for more information about the Great Gray Owl hunt]

A brief glimpse of the sun at sunrise was the only time we saw it during the entire time we were in this gray landscape, where the intensity of light in the dense overcast was about 1/50th of what it would be on a sunny day.

You have to look really carefully at every snag as you drive down the snowy roads of the black spruce forest where Great Grays like to hunt. The owls blend in so well with the conifer bark, they often go unnoticed.

Great Grays are the largest (by total body length, not weight) owl in North America. Their over-sized heads with huge facial disks are essential for hearing what is going on under the snow cover.

Great Gray Owls are mouse specialists, adept at crashing through crusty or powdery snow to depths of 18 inches to snare a vole in their talons.

The arrangement of facial feathers in two parabolas collects infra-sounds of mice running through their burrows under the snow cover and reflects it to their asymmetrically placed and shaped ears. The intensity and time difference of sound arriving at their two ears allows the owls to “focus” on the direction of the sound.

They scan the landscape under their perch by moving their head back and forth to hone in on the sounds of mice under the snow from up to 100 feet away, then quickly descend to the ground to trap their prey, completely silently. The mouse never knows the owl is coming.

Despite weighing only 2.5 pounds, these owls can break through snow crust strong enough to hold a human’s weight to get at the prey hiding below. Sharp talons snare the mouse, and the owl can quickly bring it up to its head and swallow it, head first.

Their hearing is so acute, they are able to successfully capture their prey about 60% of the time. In fact, they are more successful catching voles through snow than they are at catching gophers through loose dirt in the summer.

Great Gray Owls can hunt visually as well, and can cover hundreds of feet distance with a burst of wing flaps to grab a vole or mouse off the surface of the snow, and carry it off.