This familiar yellow finch looks almost unrecognizable in winter. In fact, the goldfinches now visiting our feeders look a bit like sparrows. The male’s bright yellow plumage has been replaced by a brownish-yellow one, while the female’s yellowish-brown feathers are now olive-green. Both male and female goldfinches will also change their bill color from orange to gray for the winter. As the mating season approaches in spring, the birds will regain their bright plumage within a few weeks.

Wisconsin goldfinches do not migrate and only travel short distances as they seek out food. They eat mainly grass or tree seeds along with the occasional berry or insect. Besides struggling to find food, these birds must also stay warm during frigid nights. To make this possible, the finch grows 1,000 new feathers for insulation. Goldfinches must also eat plenty of food during the day to fuel the shivering that heats them overnight. Humans shiver as well, but in birds, this action helps maintain a temperature of 106-109 degrees!

Did you know? The American goldfinch mates later in the year than most other birds. By breeding in late June and early July, the bird ensures that there are enough seeds for it to build a nest with as well as to feed its young.

Though Sunset and Minister Lake look pretty quiet at this time of year, there is quite a bit of activity going on beneath their icy covers. Fish are making the necessary adjustments to survive. Right now, they are quite literally chilling. As poikilotherms (cold-blooded organisms), they maintain body temperatures equivalent to that of the water surrounding them. They also alter their lifestyles. Because ice floats on the top of all but the tiniest ponds and lakes, resident fish species often school in the warmer pockets of water near the bottom. Their metabolisms slacken, and the fish become less frisky. They eat less and less as the water gets colder and colder. This is good because some of their macroinvertebrate prey are lying dormant and hidden in lake mud.

This slowdown is an advantage for ice fishers who camp out in groups to exploit the situation–unless the ice becomes so snow covered that it limits the amount of sunlight that can penetrate it. In that case, photosynthesis stops and underwater plants die and consume oxygen as they decompose. Eventually, the fish begin to die off from a lack of oxygen.

Did you know? As ice forms on top of lakes and rivers it acts as a blanket to keep the water below it from freezing. This protects the bluegill, rainbow trout, crappie, and largemouth bass in Sunset Lake from bitter winter temperatures. At the North Pole and the South Pole, where the oceans are frozen year-round, fish have evolved proteins in their blood that act as antifreeze so they don’t end up like their brethren in the frozen-seafood section.

Now that we are well into the winter months, many mammals are doing some serious sleeping. This kind of sleep has been split into two main types: hibernation and torpor. Hibernation occurs when an animal’s body temperature and heart rate drop drastically. Sometimes their body temperature is only slightly higher than the surrounding air temperatures. Hibernators such as brown bats, jumping mice, and groundhogs live off of their body fat while sleeping. However, these creatures occasionally need to wake to sip some water or go to the bathroom.

Most people think bears hibernate, but they actually go into something called torpor. This occurs when an animal’s body temperature and heart rate drop only slightly. Some other animals that enter the state of torpor are raccoons, badgers and skunks. Torpor typically lasts for a shorter period of time than hibernation. Animals in torpor also wake from their sleep more quickly than those in hibernation.

Did you know? During torpor, a black bear will lose 15%-30% of its body weight. For a 450 pound bear, that is a weight loss of about 90 pounds!

Hibernation and torpor aren’t the only survival skills that mammals have. There are many, many more…

Color change: The snowshoe hare and short-tailed weasel are brilliant examples of mammals that change fur color seasonally, but other local animals undergo similar (but more subtle) changes. The eastern cottontail, gray squirrel, and white-tailed deer all grow coats that are grayer in color. This helps them better blend in with the winter landscape. Deer also grow a coat with hollow hairs. These hairs trap more air, which serves as a fantastic insulator.

Safety in numbers: Some creatures, like deer mice, skunks, and raccoons, huddle together to conserve body heat.

Brown fat: During the fall, most of our overwintering mammals began to store energy in a special type of fat called brown fat. This energy rich fat helps generate body heat and counteract freezing temperatures. Humans have brown fat too, but only as infants.

Stored food: Red and gray squirrels have both buried nuts and seeds for the long winter. In between searching for their hidden goodies, both species may sleep in their nests for several days during especially cold weather. The eastern chipmunk has also cached food, but it stores it in underground burrows. Chipmunks will sleep in these chambers for weeks at a time, waking to nibble on their collected food.

While exploring the winter woods at CWES, you are bound to encounter several woodpeckers. The most common are hairy and downy woodpeckers, but how do you tell them apart?

Beaks: A downy woodpecker has a beak that is shorter than the width of its head. A hairy woodpecker has a beak that is about as long as the width of its head.

Size: The hairy woodpecker is about 1/3 longer than the downy and weighs almost 3 times as much!

Location: Downy woodpeckers usually stick to smaller branches, and hairy woodpeckers to the trunk.

Telling male and female woodpeckers apart is even easier. Male hairy and downy woodpeckers have a red patch at the back of their heads and females do not. As with other woodpeckers, the male is larger than the female. This allows the males to chisel deep into wood with their longer, stronger bill, where females pry under the bark with their shorter bills. These differences help a pair share food resources without competing with one another. Woodpeckers feed on all sorts of insects and spiders, and occasionally eat seeds and nuts. They are able to listen for their prey crawling beneath bark.

Did you know? The bristly feathers around a woodpecker’s nostrils keep them from breathing in sawdust.

CWES is sometimes home to a den of red foxes. This month these typically monogamous creatures are getting ready to breed. A little less than two months from now, a litter of about five kits will be born in a dirt den. Raising the kits is a family process, with mom, dad, and sometimes older siblings all chipping in. The kits will stay with their mother at least until the fall when most of them will head off on their own.

The young foxes may only live for about three years in the wild; however, they can live up to twelve in captivity. These nocturnal hunters love to eat rabbits and rodents, but will also snack on berries and insects.

Did you know? Sometimes, non-breeding female red foxes will serve as nannies and help to raise another female’s young. Also, the den in which the young are raised will be re-used for several generations.

Beneath the frozen surface of Wisconsin’s lakes and in the snow-covered forests and swamps, sleeps a very cool community of amphibians and reptiles. The disappearance of these creatures is hardly noticed during the winter months, but they are biding their time in a myriad of unique ways. While not every Wisconsin amphibian or reptile species over-winters the same way, there are some general patterns.

Many frogs (green, leopard, pickerel, and bullfrogs) swim to the bottoms of ponds and lakes. There they rest and may burrow into the mud. Their specialized body allows them to take oxygen in through their skin to breathe. In the cool water, their metabolic rates are so low that they do not feed and very slowly use a reserve of stored energy.

Painted and snapping turtles also spend their winters under deep water. They too require oxygen, but their skins are not as capable of exchanging gases as amphibians. A turtle survives this dilemma by taking water into its mouth and cloacae where the skin can exchange oxygen and carbon dioxide.

Most snakes hibernate below the frost line for as long as six or seven months. Some species, such as the common garter snake, gather in huge masses to hibernate in favorite locations called hibernacula.

Did you know? A few native frogs have the amazing ability to withstand freezing. The spring peeper, wood frog, and tree frogs can hide in leaf litter or under a piece of tree bark with up to 65% of their bodies frozen! During this time the frog does not breathe nor does its heart beat. Brain activity is un-measurable. The frog appears to be dead and rock-solid. Despite this apparently terminal condition, as temperatures warm, the frog awakens to spring.

At this point in the season we’ve already seen quite a bit of snow, but the next time the flakes fly take a moment to get a closer look. The tiny crystals you’ll see once began their lives in a cloud. There, a tiny droplet froze into a particle of ice. Water vapor began to condense and freeze on its surface, and soon a six-sided prism began to form. Eventually, tiny side arms were added to the prism and it fell down to earth. The shape and pattern of that snowflake depended on many factors: the altitude it formed at, the temperature, the humidity, and the number of other crystals it bumped into as it fell to the ground. Because of all these factors, the chances of finding two identical snowflakes are very slim.

Did you know? The average snowflake falls at a speed of 3 miles per hour. The largest snowflakes ever recorded fell in Montana. The snowflakes were 15 inches in diameter!