Bug o’the Week – And now for Something a Little Different IV – Life in the Pukak

Howdy, BugFans,

The BugLady is entertaining deadlines for two different newsletters plus BOTW, so please enjoy this article, borrowed from the winter issue of the BogHaunter, the newsletter of the Friends of the Cedarburg Bog, whose current winter issue is one of the BugLady’s deadlines.

Snow – or the lack of it – plays a significant role in the lives of animals in the Bog. An inch of snow makes it hard for ground-feeding birds like turkeys to find food, but that same inch allows mice and shrews to tunnel, hiding them from hawks, owls, and foxes. Three or four inches throw a blanket over plants and small animals but still let in sunlight. A fox can move easily in six inches of the white stuff; any deeper and it must bound, using more energy. Just as hunting success becomes more critical, hunting gets harder. A foot of snow blocks almost all of the available light from above. The drifts that immobilize deer, restricting them to the cedar thickets, act as step ladders that let cottontails feed on twigs that are normally out of reach.

shrew tunnel

Weather reports are based on data collected in a louvered box about five feet above the ground, but the vast majority of animals never get five feet off the ground – they live a scant few inches above and below the soil’s surface, and what matters to them is the air at ground level.

The microclimate that forms between the snow and the ground is called the subnivean layer, but the Inuit call that zone the pukak. Snow is an effective insulator because of the air that is trapped between the small snow particles; and like a bird’s down feathers, these air spaces are warmed by heat from beneath (from the soil, in the case of snow). These snow-lined air-spaces are constantly changing – solidifying as water vapor diffuses through the snow; compacting; melting and enlarging. The result is an insulating layer that keeps the temperature below the snow at about 32 degrees, while the air above the snow bank may be 30 or more degrees colder. It literally is a blanket of snow.

red squirrel tunnel

A subnivean layer needs an uneven landscape with some plants at ground level to keep the snow from settling flat on the earth. There is no pukak zone on the ice-covered lakes in the Bog – their surfaces are too smooth – but the hummocky sedge habitat that makes up much of the Bog is ideal. In mountainous areas, the subnivean layer keeps the snow from being “glued” to the landscape and is a factor in avalanches. By the time the snow is a foot deep (some sources say 6”), the air temperature of the pukak is stable – chill but not frigid; warm enough even for some plants to stay marginally green.

But the pukak isn’t just an exercise in physics, it’s the winter home of animals like mice, voles, moles, and, yes, red squirrels (the largest pukak-dweller), plus hardy insects and other invertebrates. These animals modify the “warm” air spaces further, creating mazes of trails that allow them to live and feed under the snow. Spring snow-melt reveals hidden pathways and seed caches, the grassy residential domes of voles (Microtus), and the trunks of small trees that the voles have girdled. .

vole house

The down-sides of pukak-living are several: it can be restrictive – no new food is introduced into the system, air quality can suffer, and it’s pretty dark. And even under the snow, the inhabitants of the pukak are not safe. Predators like shrews and weasels follow their prey into their tunnels; foxes and coyotes cock their heads and listen first, then pounce on the snow to break through to the ground. Oxygen and carbon dioxide filter readily through the snow, and the tunnels made by shrews, mice and voles provide additional avenues for gas exchange. According to folklore, voles deliberately cut “windows” in the snow’s crust to vent carbon dioxide that’s given off by respiration and by decomposing plants, but researchers conducted a series of experiments that suggest that while the concentration of CO2 may be high in some areas of the pukak, the voles don’t seem to care.

Northern plants are adapted to take advantage of snow cover, too, and they may suffer when snowfall is light. A textbook example occurred in the Bog during the winter of 2003-2004. After a dry fall, January, 2004 was bitter cold and snow-less, and by February, the frost extended deep into the ground. Although the tamaracks did leaf out in spring, their roots had been frozen and their needles soon turned brown. Twenty percent of the Bog’s tamaracks died.

Skimpy snow accumulation is hard, too, on the small, pukak-dwelling animals that depend on the climate that develops in the subnivean zone.

To discover the pukak for yourself, pick a spot with undisturbed vegetation (lawns are too uniform) and make a person-sized clearing in the snow, all the way to the ground. Lie down in it and use a flashlight to get a vole’s-eye-view of the tunnels and caverns in the airspace below the snow. To experience conditions within the pukak, make a quinzee/Quinzhee (from an Athabascan word meaning “a small snow mound shelter”). Gather enough snow to make a head-high mound about ten feet across, pack it down well, and let it settle for an hour or so. Then hollow out a living space in the middle, leaving the walls and ceiling one foot thick. It’s not an igloo – igloos are made by piling blocks of snow in a circle.

For great information about the ecology of winter, try Winter World, by Bernd Heinrich.

The first day of winter is upon us, but remember – even though we get cranky about short winter days and lengthening nights, the Winter Solstice was/is celebrated because it marks the turn-around point when days start (very slowly) getting longer.

Kate Redmond, The BugLady

Bug of the Week archives:
http://uwm.edu/field-station/category/bug-of-the-week/