A Northwoods Almanac for 2/19 – 3/4/21
TDER/SCID/RECC – Three Acronyms For Factors Affecting Winter Survival
Winter is life played out on the anvil of ice and under the hammer of deprivation. – Bernd Heinrich.
After 12 straight days of sub-zero weather, it’s time to write again about extreme cold. Late winter can be a cruel time for wildlife. There are tipping points – the proverbial “straws that break the camel’s back” – that are the difference between life and death. In his book Winter: An Ecological Handbook, James Halfpenny talks of selective winter forces that determine survival. I’ve taken four of these that I consider most important and created the acronym “TDER” to help me remember them. I pronounce the acronym “teeder,” and find the term is most easily remembered by thinking of winter forces as a teeter-totter, a balancing act with life and death consequences. The “T” stands for timing, the “D” for duration, the “E” for extremes, the “R” for repeatability.
Let’s look at each one. The timing of the occurrence of intense cold or heavy snow is crucial. For instance, in early winter, the arrival of extreme cold before the snow has come to insulate the ground can kill many small mammals and plants. Conversely, in late winter, a heavy snowstorm can kill animals that have depleted their winter store of fat.
The duration of an event is also critical. Consider how the length of time the snowpack remains can impact survival. If the snow lasts into late April or early May, some animals and plants won’t make it. Or consider the duration of a storm or cold snap. A day or two of extreme cold is one thing, but a week or more of it, like we just had, is another beast altogether.
The extremes, whether in cold, ice, or snow, can be the final straws. An organism may be able to withstand –20°F, but –40°F may be too much. Getting around in two feet of snow may be difficult for deer, but three feet or more may utterly exhaust their energy reserves.
Finally, repeatability refers to the frequency of an event. One blizzard may be survivable, but two or three close on the heels of the first may cause death. Likewise, two or three periods of extreme cold may overwhelm energy reserves and lead to mortality, although one period was survivable.
It’s all about teetering on the brink, and every animal and plant has a winter story framing their personal resilience.
“SCID” refers to the cumulating effects of Snow, Cold, Ice, and Drought. Snow lasts in our area in general about 140 days, and averages 70 inches total. In the snow belt, the average annual depth is at least twice that, with annual records over 390 inches.
Cold temperatures in our area average 5 months with lows below freezing. Our lowest lows typically fall between -20F and -30F, which puts us in zone 3. We used to be zone 4, which means our lows used to reach -30 to -40°. On the night of 2/14-15, some local areas did hit a zone 4 temperature of -37°F.
Ice remains on our lakes on average now from 11/27 to 4/17, or 142 days, according to Woody Hagge’s 48 years of ice data on Foster Lake in Hazelhurst.
As for drought, the ground is frozen. This quote from New England writer Diana Kappel-Smith’s says it all: The last trees have traded their leaves against a winter thirst. Winter isn’t only too lightless and too cold for most plants’ chemical machinery; it is a drought of momentous proportions.
Finally, what about “RECC”, which stands for radiation, evaporation, conduction, and convection? Animals are at the mercy of these four physical forces that consort to drain them of every calorie of heat they possess. I’ve grouped these forces together into the acronym RECC, because of the “wreck” animals will find themselves in if they don’t pay attention to them.
For an example, consider deer on a sub-zero day during hunting season. Typically, they lose heat through all four forces (as do the hunters). First, they lose heat by simple radiation—warm bodies emit energy. Radiation occurs even in a vacuum, so just by standing around, animals (including humans) lose heat.
They also lose heat to evaporation, because heat is lost when water changes from a liquid to a vapor. Every breath pumps heat away, and since deer don’t sweat but instead lose heat by panting, they lose even more calories by simple breathing.
They also lose heat to convection – to the wind – a factor determined by the total area of exposure, the intensity of the wind, and by the difference in temperature between the temperature of one’s body surface and the outside air. At -20°, the difference is 121 degrees between a deer’s internal body temperature.
Then every time something cold is touched, like snow, more heat is lost through conduction. The rate of conduction is heavily influenced by the thermal conductivity of the material that skin is in contact with. Dry snow conducts less heat away than wet snow since the conductivity of heat skyrockets with greater water content. Animals know well the commandment “Thou shall stay dry.”
For birds, the story is even more dire, because they have fewer physical adaptations to severe cold than most mammals. Consider the chickadees at your feeders. You do your neighborhood birds a great favor by planting conifers near the feeders that cut down the wind, and by placing your feeders on the east or south side of the house, away from the prevailing coldest winter winds.
So, a deer, or any other animal including humans, has to pick its poison relative to losing heat. Conserving energy isn’t optional for animals in the wild. These factors influence decisions they have to make every winter day, and it’s often the bottom line on whether an individual will see the spring.
Sightings – Owls, Bobcats, Gray Fox, Blue Jays, Coyote
Marge Gibson at The Raptor Education Group in Antigo, an exemplary wildlife rehab center, reports that they’re “experiencing an owl cycle.” Last week they received barred and great-horned owls from Marshfield, Plover, Merrill, Irma, Tomahawk and Wausau. The recent admissions, she noted, “are not seriously injured, which is great news, however due to severe emaciation/starvation, their condition is critical.”
Marge went on to explain why owls are having a hard time accessing rodents under the snow and ice layers: “Whereas most owls, using three-dimensional hearing, can indeed ‘hear mice’ and therefore locate them under even deep snow, ice layers prevent them from capturing their prey. Owls have specialized feathers. It is a great hunting tool, offering them silent flight. They rely on that method for effective hunting. With current conditions, [however], even if they locate their prey under the snow and by some chance manage to break through the ice, the sound of breaking ice alerts the mice to scamper.”
On a more positive note, Ryan Brady from the DNR in Ashland reports that Wisconsin is now up to 12 photo-documented great gray owls since November 5. He notes that “not surprisingly, two recent observations come from the northwest part of the state; however, two late January records [came] from southern Wisconsin, including one in La Crosse and another in Dane.”
Jerry Skierka sent me an excellent photo of a large healthy adult bobcat feeding on a deer carcass.
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| Bobcat photo by Jerry Skierka |
Conversely, Bruce Bacon sent me a photo of a small bobcat kitten trying to make it through the winter near his home in Mercer. The kitten is apparently utilizing one of Bruce’s out-buildings as its winter home. Bruce has seen no sign of the kitten’s mother, so he’s providing a little venison for the kitten now and again to help it survive. A retired wildlife manager, Bruce will trap the kitten and relocate it when the winter wanes.
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| Bobcat kitten photo by Bruce Bacon |
Mark and Mary Pflieger in Hazelhurst have a barred owl still feeding on a deer carcass they put out near their home. They also put out egg shells for the birds, and blue jays “get them as fast as they hit the ground.” We’ve never heard of this, so we’re going to have to try it! Mark also noted that they have a coyote that comes and eats fat that they spread on a tree – “it looked like it either escaped a trap or got in a fight as it was limping badly.”
And Bob Van Holdt sent me a photo of a gray fox eating sunflower seeds under one of his feeders in Custer, WI.
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| Gray fox photo by Bob Van Holdt |
Bottom line: It’s getting to be late winter, and there’s lots of hunger out there.
Celestial Events
February 20 marks the 59th anniversary of John Glenn’s first American orbit of the Earth in 1962.
The full moon (the Snow or Hunger Moon) occurs on 2/27. That same day marks our reaching of 11 hours of daylight – only three weeks to spring equinox!
And March 3 to 5 are the days when Minocqua’s average high temperatures reach 32°F, the first time since 11/27. Minocqua averages 265 days with high temperatures above freezing.
Thought for the Week
“Each species experiences the world differently, and many species have capacities that are far different from ours. They can show us the unimaginable. Thus, the greater our empathy with a variety of animals, the more we can learn.” – Bernd Heinrich, from his book Winter World.
Please share your outdoor sightings and thoughts: e-mail me at manitowish@centurytel.net, call 715-476-2828, snail-mail at 4245N State Highway 47, Mercer, WI, or see my blog at www.manitowishriver.blogspot.com.
