November 2016

Preparing for Winter

Marla Mertz, Naturalist, Marion County Conservation

It’s that time of year again. A time to dig into the fall chores of planting bulbs, taking care of household repairs, furnace checks, and getting those layers of warm clothes out of storage. We aren't the only ones getting ready for winter, so are the feathered and furred, the scaly, and the smooth and slimy. Animals are now in a rush to lay eggs, grow a new coat, build a new home, gather food, migrate, prepare for sleep, slumber, or to bid farewell and perish.

The weather changes, leaves start to change color, sunset is earlier, cool mornings are followed by warm days, and animals are preparing for winter. Children need to experience the traditions of the fall season, so encourage them to be outside!

Read this story with your children and talk about the changes in the weather and animal activity: “How The Turtle Flew South For The Winter” Keepers of the Earth, Joseph Bruchac and Michael J. Caduto, (page 157). Go outside with your child and look for signs of the change in seasons. Talk with them about what the plants and animals are doing.


Soon we will notice the grand colors of trees and shrubs as their food supply begins to slow and get stored in the roots. During the growing season, the leaves have both chlorophyll (the green color that is necessary for the plant to use sunlight to manufacture sugars for their food) and carotenoids (which produce yellow, orange and brown colors). Anthocyanin is another pigment of color that gives us the reds. The vibrant colors of fall depend on the type of tree, the amount of rain, the daytime and nighttime temperatures, and where you live. The leaves are delicate and cannot withstand the cold, harshness of winter and as the sugars within the leaf cells are used up or stored in the roots, the green color fades and in time the leaf falls to the ground.

Have your children help collect dropped leaves and make leaf prints. Remember that flat leaves work better! Place a sheet of paper over the leaf and using a stamp pad and roller or the side of a crayon with the paper removed... rub across the paper to get the impression of the leaf. When done, return the leaves outside as they make food for the soil.

Sing this song with your children to the tune of 'The Wheels on the Bus!'

The Leaves On The Trees Are Falling Down

The leaves on the trees are falling down,

Falling down,

Falling down,

The leaves on the trees are falling down,

All around the town!

What about our conifer trees, those cone-bearing trees? Conifers are called evergreen trees as they stay green all year long. They will shed their needles over a period of time, but they do not lose them all at once. If you walk through a pine grove, you will find layers of their leaves (needles). Conifer trees have a special substance found in their sap that works like antifreeze by protecting the cells in the tree needles as the temps drop.


Animals have developed some interesting ways to solve the problem of how to survive the winter when temperatures are often below freezing and food is hard or impossible to find. The ground may freeze to a depth from several inches to four or five feet. The lowest point of freezing is called the frost line. In Iowa, the soil below the frost line normally maintains a constant temperature of approximately 50 degrees year round. Larger and deeper ponds and streams do not freeze solid. There may be many inches of a solid ice layer on the water, but could be possibly up to 39 degrees F at the deepest point.

Terms that may be useful in understanding some of the different ways animals cope and survive winter:

Hibernation: A special kind of 'sleep' which is deeper and lasts longer than ordinary sleep. During hibernation the heartbeat and rate of breathing are much slower than when active, and the body temperature drops close to that of the surroundings. The true hibernator awakens slowly.

Torpor: A state of physical or mental inactivity; lethargy.

Estivation: A prolonged torpor or dormancy of an animal during a hot or dry period.

Migration: Seasonal movement from one place to another.

Cold blooded: Require outside heat (like the sun to warm environment) to provide energy for movement and to sustain life.

Warm blooded: Animals (chiefly mammals and birds) that maintain a constant body temperature typically above that of the surroundings; also called homoeothermic.

Dormancy: Normal physical functions suspended or slowed down for a period of time as if in a deep sleep, e.g. mourning cloaks, red admiral, painted lady butterflies.

Hibernation: In Cold Blood

If you are a hibernator or stay active in the winter, food storage and fat building is extremely important for survival. As temperatures approach the freezing point, they need to have built up quite a fat layer, started the hibernation process, migrated, or be able to survive in an immature stage. However, cold-blooded animals need outside heat to warm their environment to provide enough energy for movement and gathering food. Fishes, frogs, snakes, and turtles really have no way to keep warm during winter.

Sometimes, we see painted turtles crossing the road, or in a pasture traveling to another watering hole. This travel is migration (traveling from one place to another). Maybe they are migrating to another area to lay eggs, or to another water area that holds more of their desired food, or if it is getting colder, they are returning to their desired area to begin their hibernation process. Turtles are quite sensitive to changes in the environment and bury themselves in the muddy bottoms of waterways as temps drop and remain cool. They do not have to breathe in air, because oxygen can be taken in through their skin. Their heart rate will drop to approximately one beat every five to ten minutes. (Now, that’s cool!) How many times does your heart beat in one minute?

Snakes also have to build a fat layer; it’s going to be a long time before the ground gets warm enough for them to have the energy to find food. Most reptiles can find a place to settle in for the winter in hollow logs, another animal’s burrow, rocky crevices, under woodpiles and stumps. Some species of snakes group together in one place. There may be hundreds of them together in a den or cavern. A group of snakes at one site is called a “hibernacula.” They must hibernate in an area that is below the frost line. In the spring, the sun again warms the soil and rocks and slow movement begins until their body reaches about 72 degrees.

Hibernation: In Warm Blood

Remember, warm-blood animals maintain a constant body temperature. Humans are warm-blooded and have a constant temperature at or about 98.6 degrees. The range varies in other animals, but each has their own consistent range. In Iowa, there are very few “true hibernators.” Most of them usually go into a torpor stage. Torpor can be described as a suspended animation.

True hibernation in Iowa is normally found in groundhogs (woodchuck), ground squirrels, jumping mice, a few other rodents, and bats. Hibernators actually are known to curl into a tight ball and reduce their normal levels of heart and breathing rates. They also reduce their body temperature and metabolism. The groundhog is probably the largest of Iowa’s hibernators.

Torpor v Hibernation

It can be confusing as to what the difference is between hibernation and torpor. Torpor is a short-term reduction of body temperature and normally occurs in their normal daytime home. Hibernation is actually torpor but for of an extended period of time.

Bats may both migrate and hibernate. It is important for them to store fat and that can occur during migration and/or when they reach their hibernation destination. Many bats move to caves or cavernous structures. The big brown bat is known to overwinter in Iowa buildings. Their metabolism is extremely slow and the utilization of their fat reserve is also reduced. If hibernating bats are disturbed or aroused, their reserves may deplete rapidly and diminish their chances of surviving winter. Learn more about bats here.

Most large mammals continue to be active during our cold winters and do not migrate or hibernate, but have special features to help them survive. Beaver and Muskrat grow an extremely dense undercoat that lies beneath their long guard hairs (see photo left of beaver guard hairs) for protection under icy waters and cold conditions. Whitetail deer have hollow guard hairs that help insulate their body.

Migration: Winged Ones

We enjoy birds year round. They are easy to talk about because they are available. As the fall season approaches, the skies become alive with ducks, geese, white pelicans, egrets, herons, kettles of turkey vultures, osprey and more. We noticed many birds in the area throughout the summer because of their breeding and fledging activities. Many birds can survive the long, cold winter months by changing their food habits and moving into protected habitats, such as woodlands and dense areas of grasslands.

Other birds may begin to fly a little further south to locate open water, or warmer climates where food is still available. Some birds will stay within the United States, while others continue south across the Gulf of Mexico to South and Central America. These long-distance fliers beyond the Gulf are called Neotropical migrants, living half of the year in the tropics and returning to breed in the United States.

Iowa has numerous reservoirs where areas of major rivers are open in the winter allowing for northern birds to winter in Iowa, like bald eagles. Ducks can get through winters in cold, open water, due to the fact they have very warm feathers that trap air and have very special veins in their featherless feet and legs to keep them warm. They just need to be able to find food in open water.

Monarch butterflies do not overwinter in Iowa. They migrate and spend their winters in the highlands of Michoacan in Central Mexico. According to Iowa State University Extension entomologists, the monarch must be re-introduced into the state every spring by north-bound dispersal of last year’s butterflies and their offspring. Have you ever seen a tagged Monarch or a large group of monarch butterflies huddling on tree branches and feeding on the flowers of prairies and grasslands? Check out the Monarch Watch program to learn more about monitoring monarch populations.


Some insects go through a period of time that improves their chances of survival. They cannot eat, reproduce or even move around. Their physical functions are slowed down as if they are in a deep sleep. Overwintering insects may be hiding in leaf litter, under the bark of a tree, or deep into the soil. Many insects perish before winter arrives and rely on eggs laid in protected areas to begin new life in the spring.

As temperatures drop, male bumblebees and worker bees die. The Queen is the only one to prepare for hibernation in a hole in the soil, in leaf litter, or rotting stumps and logs. She can stay in hibernation for six months or more. In late spring, she emerges, builds a nest and creates a new team of bees.

Another fascinating insect that creates one of the most elaborate nests is the bald-faced hornet. When leaves drop, the nests they build become visible to us within tree limbs as along woodland edges. These unique nests are only used for one season. Animals and birds tear them apart when they become visible and eat any larvae or hornets that remain. By the end of the summer, males and new queens produced in late summer leave the nest to mate. All of the queens will go into a dormant state filled with eggs, as the old queen and males will perish. As the new queens emerge in late spring, they choose a place that will be sheltered from weather, lay many eggs (all sterile daughters) and those young of the year create the more sizable nest and gather food while the queen rests and lay more eggs.

A few butterflies also survive through dormancy in an adult stage i.e. the mourning cloak, red admiral, and painted lady. The adult butterflies are usually tucked into crevices in logs or underneath loose bark on trees. There may be sightings of these butterflies flying during the winter on a warm day. Some species will lay eggs on twigs and leaves and await the coming of spring. Hibernating caterpillars survive by burrowing into the leaf litter at the base of their host plants as fall approaches. Feel free to look up the more scientific facts of the amazing insects that overwinter in Iowa and the natural antifreeze they produce that keep them from freezing.

View Preparing for Winter photo album in Google Photos!