Winter in the Woods

Listen Up! 

With so many studies touting the cognitive benefits of learning a 2nd language, it got us thinking we should be helping kids to learn the language of birds. Birding by sound is the way most birders first identify birds in the field, being outside is relaxing, and a walk in the woods is a great way to spend time with your kids.  Wintertime is the perfect time for kids and adults to learn the common birds of Eberwhite Woods. There are only a few species present in the woods in the winter, they all have distinct sounds, and with the leaf cover gone, they are easy to spot - it helps learning to see and hear the bird at the same time. Come spring, the woods will be filled with the sounds of migrants and summer birds, so head out now on a hike to learn these few winter birds in the woods. (we feel the iPhone Chirp! app is the best tool for helping kids learn their bird songs, otherwise the Cornell AllAboutBirds site has many bird song and call sound clips)

Red-bellied woodpecker

Black-capped chickadee

Northern cardinal

Great horned owl

Red-tailed hawk

Tufted titmouse

Blue jay
Mourning Dove

Getting Kids out in the Woods!

A number of classes headed out in the woods last week to explore the signs of winter. There was great snow cover for viewing tracks and lots of evidence left by the resident great-horned owls. 

Rabbit tracks leading to a burrow, and the kids checking it out!

Some amazing finds left behind from the resident great horned owls. Left: A large owl pellet one of them coughed up right before the kids headed out in the woods with the front teeth of a rabbit (center of pellet) and the lower jaw (left part of pellet). Right: Kids getting a close-up view of the owl pellet.

A rabbit intestine left behind in the woods presumably from an owl kill - how great to say, "Who wants to see a rabbit intestine?" and have the whole class run over yelling "me!"

Fun in the snow!

The Subnivean Zone, life under the snow

Some animals are more active than it appears during long, snowy winters.

Reprinted from: https://www.canr.msu.edu/news/the_subnivean_zone_life_under_the_snow_part_1
February 3, 2014 - Author: Julie Crick, Michigan State University Extension

Each year as the snow begins to accumulate across our Michigan landscapes, many of us assume that the animals have bedded down for the winter, sleeping away the cold winter days and nights awaiting the spring thaw. In reality, the snow actually creates a sheltered environment for some small animals, allowing them to stay fairly active during the winter months.

Next time you take a winter walk through your woods, Michigan State University Extension recommends that you pay attention to the tiny tracks in the snow. Look closely, these tracks may actually be the tracks made my mice and other small animals as they travel back and forth across the snow. Follow the tracks a little further, and you will likely see that the tracks disappear into a small hole in the snow. You have just found an entrance into the “Subnivean Zone”, a place under the snow where mice, voles and other animals make their cozy winter homes.

The Subnivean Zone

The word “subnivean” comes from the Latin words for under (“sub”) and snow (“nives”) and refers to the open, shallow layer that usually forms under deep, layered snow. The layer can form two ways. The first is when vegetation, leaf debris or trunks and branches physically hold the snow up, which creates an open space that can be used by the small mammals. The subnivean layer can also be created as the snow is warmed by the ground, and sublimates into water vapor that moves up through the snow pack. This sublimation, or the transformation of solid snow particles into the moist gas, changes the lowest snow layer into small ice particles that then act as an insulating roof. The sublimation also occurs when the snow is physically help up, providing further insulation. The result is a humid winter habitat with relatively stable temperatures around 32 degrees.

What types of animals live there?

There are a variety of animals that live in and depend on the subnivean zone for winter survival. The most common are small mammals including mice and voles. These animals spend most of their winter in the subnivean zone, eating plants, seeds, bark from bushes and shrubs. Both mice and voles will sometimes cache, or store up small amounts of food, to ensure a steady supply. While these animals are active throughout the winter, they do spend small amounts of time huddled together in a deep sleep, waking occasionally to feed.

The mice and voles develop a series of tunnels under the snow to make travel easer. The tunnels lead from entrances to sleeping areas and to known sources of food. The entrance holes double as ventilation shafts, allowing the carbon dioxide created from animal respiration as well as carbon dioxide released from the ground to escape. This helps to keep the concentration of the suffocating gas to non-lethal levels.

In the spring or during a thaw, the tunnels become visible. This allows us to ponder the winter movement of the creatures living in the subnivean zone. The evidence of the tunnels can either be hardened snow in winding patterns that lingers after a thaw or trails of beaten down or chewed grass. Whatever the evidence you find, it is awesome to imagine life under the snow.

Small mammals also find cover from predators under the snow. This is important because they typically lack winter camouflage and may be seen from long distances when travelling across the stark white snow. Despite being out of sight, these animals are not exempt from predation.

Everyone has to eat – especially in the winter

Predation in the subnivean zone can occur two ways. The first is by predators using the established tunnels to find the small animals; the second is from predators above the snow.

The most common predator under the snow is the “ermine,” or a weasel whose coat becomes white in the winter, usually with a black tip at the end of the tail. Ermine are long and slender, allowing them to burrow into the snow using entrances or ventilation holes to begin the hunt. The ermine follow the tunnels until their meal is found. Ermine may also take over the tunnel and make it their own.

Winter with snow pack can create slim pickings for other predators that do not have the ability to squeeze into the tunnels. Predators such as the fox, coyote, wolf and owls often prey upon the small animals when they travel out of the protected tunnels. The tunnels do not offer unequivocal protection, however, as these predators may also hunt the small animals from on top of the snow.

Fox, coyote, wolves and owls have a keen sense of hearing and can actually hear the activities of the animals moving around in the subnivean zone. The sounds allow them to pinpoint the location of the animals, causing them to jump head long into the snow with the hopes of coming up with a meal. Owls listen from their perches and use their talons to dig into the snow for a meal. And the cycle of life in the forest continues….

Next time you are walking or skiing on the winter snowpack, Michigan State University Extension reminds you to remember to look for clues that animals are actively moving around just below your tracks, in the subnivean zone. 

Here is evidence of the subnivean zone in Eberwhite Woods - tunnels visible after the snow above had melted:

Have you seen the new entrance signage at the Eberwhite School parking lot? 

We moved a boulder from the Zion Church meadow to the entrance - it has a neat story!

This glacial erratic is a granitic gneiss (pronounced: nice), a type of metamorphic rock. Metamorphic rocks are formed when an original (parent) rock is changed by high temperatures and pressures and a new rock forms. The parent rock for this glacial erratic was granite, a type of igneous rock.

Glacial erratics are rocks that were transported by a glacier and left behind when the glacier melted. They can range in size from pebbles to large boulders and may have been carried hundreds of miles by the glacier. The name erratic comes from the Latin word errare, “to wander”.

Where did this large glacial erratic come from?

This rock was most likely deposited (dropped) in the meadow next to Eberwhite Woods ~20,000 years ago – that is pretty recent geologically – but it is actually a very old rock that was carried here by a glacier that used to cover Ann Arbor.

Without age measurements, it is impossible to know for sure, but there are two possible source rocks for Eberwhite Woods’ granite gneiss. – one guess is based on appearance and one guess based on ice-flow directions.

The rock looks the same as rocks from the Carney Lake dome in the western Upper Peninsula. These rocks have an age of about 3.5 to 3.6 billion years. Even though the Eberwhite Woods’ Erratic looks like the rocks at Carney Lake, rocks from that region are not known to have been transported to the Ann Arbor area by glaciers.

In terms of ice transport, a more likely source is the ~2.7 billion-year-old Wawa-Abitibi belt in Ontario, just north of Sault Ste. Marie. Rocks from this area are common in southern Michigan.

We can’t be certain which of these two areas our rock came from, but we can say the rock is one of the oldest in the world and formed the core of the North American continent. It is almost certainly Archean in age, at least 2.7 billion years old, and possibly 3.5 to 3.8 billion years old. It is part of the terranes (fragments of the Earth’s crust) that were joined to make the North American continent.”

Left: A map of the Great Lakes region of the United States and Canada overlain by a geologic map showing the location of the two possible source rocks for Eberwhite Woods’ Glacial Erratic – either Carney Lake Gneiss or Wawa-Abitibi terrane. The approximate distance from the Carney Lake Gneiss to Ann Arbor is 520 km (320 miles) and from the southern portion of the Wawa-Abitibi Terrane to Ann Arbor is 450 km (280 miles).

Right: Reconstructed extent of the Laurentide Ice Sheet approximately 21,400 years ago – this is a continental glacier – over 2 miles thick in places, that covered most of Canada and parts of the northern United States with, reconstructed ice-flow pattern of the Laurentide Ice Sheet in the Great Lakes Region 21,400 years ago. Note: The glacier covered all of Michigan (dark blue outline), the flow pattern is the solid blue.