The American Goldfinch: A Bird of a Different Feather

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 The male's bright yellow plumage has been replaced by a brownish-yellow one, while the female's yellowish-brown feathers are now olive-green.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.

Learn more: Cornell Lab of Ornithology

​Glimpse Under the Ice!

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.

Learn more about fish senses and adaptations: Young Naturalists

​Torpor vs. Hibernation

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!

Learn more: Eye on Nature

Other Amazing Adaptations

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.