The outdoor thermometer has not budged from its 0 degree F reading in the past two days. The gray squirrels are absent, but the red squirrels poke their head out every now and then. The one constant feature in the backyard, regardless of the weather, is the Black-capped Chickadees. A family group of seven chickadees makes the rounds of the feeders once or twice a day, pausing only briefly in the lilac bush a few feet from the feeder to drill out the core of a sunflower seed before swooping back to the feeder for another.
I can usually tell what sort of weather conditions are coming using my “bird barometer”, which consists primarily of monitoring the intensity with which birds are feeding at the various feeders scattered around the backyard. About 24 hours before a big thunderstorm or a dreary day with steady rainfall, those feeders are humming with activities of multiple individuals of a variety of species. For example, yesterday was cloudy but mild, but dozens of finches, sparrows, and chickadees crowded in or around the feeders for several hours in the morning.
These ground-feeding birds were reaping the benefits of all the spilled seed from the multiple gangs of finches, chickadees and nuthatches vigorously attacking the feeder above them.
Today (just 24 hours after the feeding frenzy) is rainy and cold, and the feeders are quiet. An occasional Blue Jay visits, but even the Chickadees are absent. How do birds predict such changes in the weather? Do they really have an internal barometer?
In fact, they do. A group of hair cells in the Vitali Organ, or Paratympanic Organ (named for Giovanni Vitali who discovered them about 100 years ago) in the middle ears of birds is thought to be responsible for detecting changes in atmospheric pressure of just 10-20 mm of water (about 0.75-1.5 mm of mercury). Such exquisite sensitivity allows birds to maintain their elevation while flying long distances within 10-20 feet of desired altitude — essential for navigation, but it also allows birds to sense changes in barometric pressure at ground level, especially the declining barometric pressures that signal approaching storm fronts. Input from these specialized cells due to barometric pressure changes then causes abrupt and marked changes in bird behavior, as they prepare for and protect themselves from changes in the weather.
Are birds the only animals with this unique ability? Hardly. Most animals can sense impending changes in the weather, using a variety of other cues (infrasound, daylight, smell (ozone?), static electricity, etc.). But only one group of mammals may possess the type of middle ear barometric pressure detectors present in birds. Can you guess what group that might be?
An interesting reference on this subject can be found here: Von Bertheld and Gianessi, 2011. The Paratympanic Organ: A barometer and altimeter in the middle ear of birds? Journal of Experimental Zoology 316 (6): 402-408.
Even though I’ve just read that 2015 was the hottest year in historical weather record-keeping (2 degrees F above average world annual temperature), the backyard here is buried in the deep freeze. Several of my fellow bloggers have been posting queries about how animals survive conditions like this in the wild — or how humans who live and work outdoors all winter survive these extremes. So, being somewhat of an expert on this topic once upon a time, I’m going to try to explain how they do it.
First — the challenges of winter at far northern latitudes:
- low temperatures mean warm-blooded animals need to turn their heat producing furnaces to high to offset heat lost to the environment
- wind, sleet, and any precipitation carry body heat away even faster than just being surrounded by cold air
- the sun is low in the sky and it’s often cloudy and overcast, so radiant heat input is hard to come by
- where’s the food? Summer production is long past, food is buried under snow, other animals got to it first — so how does a warm-blooded animal get enough energy daily to fuel the heat-producing furnace?
1. Prepare for it: Those chilly fall mornings and waning daylength are signals that challenging days are ahead. Animals prepare for the challenges of winter by hoarding or stashing food in places where they can find it later. Usually, there is a flurry of activity at bird feeders as birds and squirrels take seeds to their winter roosting sites.
And — a new set of freshly molted feathers in the fall not only disguises once brightly colored birds, but provides a nice, new downy coat of insulation. An under coat of dense fur beneath longer guard hairs helps keep mammals warm in the winter.
2. Eat like crazy — in order to put on a nice layer of fat reserves. This strategy works better if you’re a fleet-footed mammal, because when birds put on too much fat, they can’t fly. In addition to the insulative value of a layer of fat, it does provide an energy reserve for overnight energy expenses and the days when foraging for food was inadequate.
And — since there aren’t many insects active in the winter, avian insectivores like chickadees switch their diet to take advantage of the high-energy content in seeds.
3. Hide from the worst extremes: Chickadees, nuthatches, and woodpeckers find a refuge from extreme temperature and wind in a roost hole. Some sparrows and larger birds like Robins and Blue Jays huddle in the thickest part of evergreen vegetation which protects them from the effects of wind and precipitation. Many mammals retreat to underground burrows, tree cavities, or leafy nests to hide from extremes.
To be continued tomorrow with more solutions….
The thermometer read -13F (that’s -25C) in the backyard this morning — birds, squirrels, and deer were sleeping in until the sun rose high enough to hit the trunks of the trees and the bird feeders (around 10 a.m.). And then the rush was on to grab peanuts, eat suet, and grab a few sunflower seeds before disappearing back into some warmer niche.
These little birds look like balls of fluff, with their feather insulation expanded out for maximal warmth. But a stiff wind today makes heat conservation pretty difficult with wind chill temps hovering around -35 F!
I really dislike going out in weather like this, but animals have no choice. Foraging hours are shorter on extremely cold days, and the birds prefer the high caloric fuel to make energy ends meet overnight. Of course, retreating to a nicely insulated nest hole helps too.
The other day when I was out walking in the far backyard (marshy swamp area) just before dusk, I stopped to look at a snag (dead stump) with a variety of different sized holes in it, when suddenly a Hairy Woodpecker flew out from one of the holes. A moment later another woodpecker flew out from the same hole. They might have been a breeding pair that decided to share their heat in an old nest hole — which is a great way to survive this frigid weather.
It’s nesting season for some of the resident birds. Having staked out a territory and driven off the competition, it’s time to find that perfect little home in which to raise the kids this year. For some species, the safest place is a cavity in a tree or nest box, where the offspring will hopefully be safe from predators. The other day while I was down by the pond in the far backyard looking at turtles, a pair of Black-capped Chickadees were flitting in and out of a notch in a dead branch just a few feet away.
This cavity may have been used by a previous owner (e.g., a woodpecker) because the entrance is quite a bit larger than the chickadee is. Nevertheless, this pair is modifying the cavity to suit their needs this year — for example, the typical cavity for a chickadee nest is about 8 inches deep. After excavation, they will add a layer of moss and small sticks, and then another layer of soft fur to line the nest cup. It’s quite a production.
But the number of suitable cavities of just the right size are limited, and there are lots of chickadees, House Wrens, Tree Swallows, and Bluebirds that require one about this size to start building their nest. While I was watching the courtship activities of the osprey pair at the marsh the other day, I saw some of this interspecific competition between chickadees and Tree Swallows, each of whom seemed to be claiming a cavity in a tall, dead snag.
I didn’t stay to see who got control of this cavity. Tree Swallows are a little larger than chickadees and weigh about 50% more, so it’s possible they might have ousted the chickadees and claimed this cavity for their own home. I’ll have to check back later to see who “won”.
Earlier this year than last, but probably average for this northern climate, winter began with a flurry of flakes this morning.
The warblers are back. They must have flown in with the last storm front this week and are just as busy as they were last spring flitting about the trees and shrubs in search of food. Since they don’t sing or chirp very much on their way south, I discovered the best way to find them was to listen for Chickadees making the “dee-dee” call. Every time I found/heard a flock of chickadees, I saw a variety of warblers with them.
It seems the warblers like to hang out with the local insectivores, forming mixed flocks of several species all cruising through the shrubbery and leaves together. Chickadee calls impart a wealth of information about the environment, especially the presence of potential threats, so perhaps migrating warblers rely on the local chickadee experts for information. In addition, more eyes to watch for predators equals greater safety.
Warblers are notoriously difficult to identify in the fall, mostly because they are not singing and the typical bright and distinctive male plumage may be dulled, looking more like the less distinctive female of that species. Adding juvenile birds into the mix further confuses us. So here’s a bird ID quiz.
Below are two photos of what I thought was two individuals of the same species.
What do you think? One species or two? List your reasons in the comments, and I’ll give you the answer tomorrow.
Almost every walk in the backyard these days reveals another bird working on its nest. This time it was a pair of Black-capped Chickadees excavating a nest in a rotting stump about 2 feet tall and right next to the trail. The birds had no hesitation in flying in and out of the nest with me standing only about 10 feet away. While one bird chipped away at the interior of the stump, its mate oversaw the process from a nearby shrub, but was silent (I guess I must not have been too threatening).
Once she has finished with nest construction and laid her clutch of eggs, the female incubates them continuously for about two weeks. During this time, the male brings food to her, instead of her leaving to find her own food and allowing her eggs to cool. Embryos develop rapidly with this constant attention and chicks hatch within two weeks. Both parents then feed the chicks which grow rather rapidly and are lured out of the nest to be fed by their parents after as little as 10-12 days. This rapid development from egg to fledgling (about a month) minimizes the risk of predators finding the nest and devouring eggs or chicks.
I asked my grandkids this morning: what do you think of when you imagine intense cold like we have today (-22 F at 7 a.m. this morning) ? They said — white, blue, partially transparent — sort of like this.
But weather forecasters reserve the color purple for the really intense cold.
Not the humans who flee the frozen north, but the little birds that tough out our sometimes harsh climate. The snowfall went on and on, but it wasn’t cold and there was a fair amount of activity at the feeders. A few stoic poses from the fantastic four (survivors).