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.

Stark! Cold! Lifeless (almost).

That was the North Shore of Lake Superior this weekend.  So much wind they closed the lifts at Lutsen mountain, and the outer doors of our motel blew right off their track.

Lake Superior, Tofte, MN

There are some interesting ice formations on the frozen part of the lake.

Wind and cold temperatures make for a stark landscape.  It’s more attractive with some people in it — cold hikers!

Lake Superior, Tofte, MN

Lake Superior, Tofte, MN

Lots of frozen waterfalls along the cliff walls of the lake.

Lake Superior, Tofte, MN

Glittering shards of ice litter the shoreline of the lake.

American crow

Crows and ravens always seem to be out hunting for food regardless of weather extremes.

crows feeding on roadkill

Most often the animals you might see are feasting on roadkilled deer.  Larger predators like wolves and coyotes arrive first, then eagles, ravens, and crows. We saw several of these feeding sites along the north shore highway.  Image from a Storyblocks Video. 

Just being out in this environment for a couple of hours at a time makes me marvel at the abilities of animals to survive in it.

Bird of the north

A bird synonymous with high elevations (except the Sierras of California) or high latittudes (Canadian coniferous forest) — Gray Jays.  These diminutive cousins of our familiar Blue Jay can be found in spruce forests, or where jack or lodgepole pine are present. We found them at the southern limit of their range at Sax-Zim bog in north-central Minnesota, but they can also be found in northern Wisconsin, Michigan, and parts of New England states in the U.S.

gray jay

With their small head, shortened beak, and dense body feathers, they are well adapted to the extreme cold of the northern coniferous forest.

gray jay

The beak is shaped more like a chisel, with a sharp pointed end that is handy for stuffing food items into crevices under bark.  This is a key strategy to their winter survival.

Gray Jays are food hoarders.  They stash excess food during the summer and fall into nooks and crevices of particular tree species, first lubricating it well with saliva and forming it into a ball and then stuffing it into place with their bill.  Either the saliva or substances in the tree bark must have anti-bacterial properties because these food caches do not deteriorate over time. That and the deep freeze of their winter habitat ensure that there is always food available all year, and especially during the winter when the usual nuts, berries, and other animal prey have disappeared.

gray jay

Gray Jays are attracted to feeders and other sources of free food in the winter, like this frozen deer carcass left there purposely to provide a source of fat and protein for local wildlife.

The birds here are probably happy to stock up on fat and protein, as they will start their breeding season in a month or two, well before winter temperatures and precipitation have moderated.  Gray Jays have been seen feeding their chicks at -20F!  That’a a tough bird — well-adapted anyway.

gray jay

Like other jays, Gray Jays are social breeders, utilizing the help of juveniles from the previous breeding season to help feed the current clutch of chicks.

Pileated times two

It’s a great day when I get to see our largest woodpecker, the Pileated, in the open and can get organized quickly enough to get some photos of the bird.  It’s an even greater experience to see a pair of them pose for me close enough to hardly even need the telephoto lens.

a pair of pileated woodpeckers

The pair played ring around the Buckeye tree for a few minutes, usually with just one of them in view at a time.  Notice how they have their red crests somewhat erected — more on that later. (Taken through the window, so somewhat blurry)

These birds are truly impressive, almost as large as a crow in body size, with a striking black and white pattern, a flaming red crest, and an impressive chisel at the end of their long beak.  I wouldn’t want to try to take one of these guys out of a bird net!

The pair stay together all year on their territory, though its size or shape may change in area seasonally, as they expand it in search of food in the winter.  Although I have heard them calling out in the wetland and occasionally seen one of them flying around, I’ve never seen them together, and here they both were at the suet feeders.

pileated woodpecker female

The female Pileated Woodpecker sports a black mustache, which makes her easy to tell from the red-mustachioed male. Note:  in comparison to this large-bodied bird, a Downy Woodpecker’s body length would stretch only from one suet plug to the next.

pileated woodpecker male

Such a handsome guy! Unlike the little Yellow-bellied Sapsucker who dines for minutes at a time, the Pileateds ate very little of the suet before moving on.

Even though this is a mated pair, their harmony seems to depend on an established social hierarchy — i.e., whoever gets to the food first owns it, no sharing.  It could be that males are a little more possessive about this, but I didn’t observe whether the female would defend her own feeder from him in a similar manner.

pileated woodpeckers

While the male was feeding at this suet feeder, the female came over and perched nearby.  She might have thought this one had better suet than the one she had just left?  But in response he raised his crest feathers, and then so did she.

pileated woodpeckers

Then she tried to land on the other side of the feeder log, and that didn’t go over well with him at all. Notice those red crest feathers standing out from the back of his head.

pileated woodpeckers

Threat over, he goes back to feeding, and she pretends to hide behind a branch, crest feathers relaxed.

So, if you have to compete with your mate for food, then what’s the advantage of staying together during a time when food is so limited in the winter?  To protect the area from other Pileated Woodpeckers that might want to establish a breeding territory there?  To get a jump start on the breeding season, without having to spend time and energy looking around for prospective nest holes?  Perhaps these advantages outweigh the disadvantage of competition for food, or perhaps there really is no competition because the male and female forage in different ways that nets success for both.

Coping with cold

Continuing on the theme of what animals do to survive winter cold, it can be just as much of a problem being large as being small in intensely cold weather.

deer-in-the-winter woods

When you are big-bodied, there are few places to take refuge from cold temperatures and wind chill, which increases the rate of heat lost to the cold environment.  In addition, large-bodied animals would need a large amount of food per day to maintain a warm temperature, and winter is typically the most difficult season in which to find it.

The twins munched their way across the backyard on a cold morning recently, in search of some nutrition from twigs and stems.

The twins munched their way across the backyard on a cold morning recently, in search of some nutrition from twigs and stems.

Their heavy winter coats insulate their core, but lots of surface area of exposed extremities could be vulnerable to high heat loss.  At sub-zero F air temperatures, even large-bodied deer will have to expend energy to stay warm. Daily food consumption is too meager to support that expense, so deer have to dip into the fat reserves they built up in the fall eating energy-rich foods like acorns.

From Outdoor Life:  What deer eat.  Aug 31, 2012

From Outdoor Life: What deer eat. Aug 31, 2012

The White-tailed Deer strategy for surviving winter cold is a conservative one — reduce energy expenditures to conserve body fat.  They let their extremities chill to the same temperature as their environment, so little heat is lost there.  They eat snow (for moisture), which lowers their core temperature and heart rate, and thus their whole-body metabolism.  They reduce their daily activity, spending less time foraging, which also saves some energy.  In short, deer coast through the winter relying on their fat reserves, hoping for an early spring (don’t we all!).


Surviving the long, cold winter

You don’t appreciate the impact that a long winter and a cold spring has on wildlife until you see a couple of survivors like this.

This buck has catabolized a lot of what was probably a massive frame of muscle, as he slowly starved during our long, cold winter and delayed greening-up this spring.

This buck has catabolized a lot of what was probably a massive frame of muscle last fall, as he slowly starved during our long, cold winter and delayed greening-up this spring.

This animal doesn't look quite as emaciated, but has something strange going on with its fur which has turned splotchy white in big patches.

This animal doesn’t look quite as emaciated, but has something strange going on with its fur which has turned splotchy white in big patches.

I was out looking for warblers at one of the local parks when I saw a small herd of four deer working their way through the shrubs coming toward me.  They were so intent on grabbing every green leaf they could, they just ignored me, even as I walked closer to them.  Leaves have only just emerged from buds the last couple of days, and so it has been more than six months since these deer had anything resembling nutritious food.  No wonder they are in such bad shape.

Now, he needs to grow a new set of antlers for the coming rutting season, an added energetic expense for an already energy-taxed animal.

Now, this buck needs to grow a new set of antlers for the coming rutting season, an added energetic expense for an already energy-taxed animal.