The Friends of the Wild Flower Garden

P. O. Box 3793
Minneapolis MN 55403


Winter Survival of Warm-Blooded Critters

by Tammy Mercer


The rich diverse habitat of the Eloise Butler Wildflower Garden and surrounding Wirth Park creates an important place for many birds and mammals to survive harsh Minnesota winters.

Black-capped chickadees
Chickadee
Black-capped Chickadee. Photo by Tammy Mercer.

Black-capped chickadees are remarkable birds with several strategies for surviving northern winters. They form organized flocks that might include such other wintering species as Downy Woodpeckers or White-breasted Nuthatches. Flocking brings more eyes to watch for danger and find food throughout the winter range. At night the birds may shelter in small cavities or dense evergreen trees.

Chickadees glean insect eggs, caterpillars, pupae and adults overwintering in tree bark and other plants. With strong legs, they can hang upside down to find food that other birds might miss. They also search for seeds with a high fat content. Prairie plants are a good source, because their sturdy stems remain standing while other plants are blown over and buried by the snow. Chickadees hide extra food in tiny nooks and crannies to save energy later.

Chickadees fluff up their especially dense feathers for extra insulation and keep their body temperature high by spending every moment of daylight foraging for food. Their high metabolism can turn food into an insulating layer of fat by nightfall when they need it most. Their most remarkable adaptation is the ability to lower their body temperature at night just enough to conserve energy and make the fat last until morning on all but the most extreme winter nights. They need to survive the night with just enough energy to shiver enough in the morning to raise their body temperature so they can fly off and feed again.

When weather conditions are at their most extreme, some birds will not survive. Bird feeders help them find more food while expending less energy searching, which ultimately may help them get through the night.

Dark-eyed Juncos, Pileated Woodpeckers, Great Horned Owls
Junco
Dark-eyed Junco. Photo G D Bebeau.

Dark-eyed Juncos breed far north of the Twin Cities and migrate south to winter in the Garden. Like chickadees, they stay in organized flocks through the winter. By day they follow a regular route foraging for seeds. At night they roost together, usually in a dense conifer offering protection from the wind.

Pileated Woodpeckers need large tracts of mature forest. The Wildflower Garden alone is too small, but the Garden combined with Wirth Park makes a great territory for them. Mated pairs stay in their breeding territory year round, foraging together and probing tree bark for wood-boring insects. They use nesting cavities for roosting separately at night, and their large size helps them maintain their body temperature.

Pileated Woodpecker
Pileated Woodpecker.

Great Horned Owls are active all winter in and around the Wildflower Garden, using their excellent sense of hearing to find small rodents under the snow. They also catch such larger mammals as rabbits and squirrels. Because of their larger size, owls lose less heat through their skin and have lots of feathers to keep them warm.

Many species of mammals are also able to survive a Minnesota winter in the Wildflower Garden. The Mink is a long, slim animal that stays active all winter. Mink have a high metabolism and thick fur to help keep them warm, but they store little fat and must keep hunting and eating all winter. They are good hunters on land and in water and eat anything they can find, including the well-fattened rabbits, mice and voles that are plentiful in the Garden throughout the winter.

Chipmunks
Chipmunk
Chipmunk (or Seven-striped Ground Squirrel). Photo G D Bebeau.

Anyone who has watched chipmunks at the shelter feeding area may have noticed them stuffing their cheek pouches full of seeds. When their cheeks appear ready to explode, they scamper off to their hiding place to unload and then go back for more. Their hidden store of food, or cache, is usually located in an underground burrow and might include such seeds and nuts as acorns, pine cones, sunflower seeds and whatever they found at the bird feeders. They usually collect far more food than they will need.

When temperatures drop and the snow falls, chipmunks will close up the burrow entrance and go to sleep.

Their body temperature drops several degrees and breathing slows to 20 breaths per minute. This is a semi-dormant state, not true hibernation. Chipmunks awaken frequently during the winter to munch on their cache, eliminate and maybe even have a quick peek at the outside world on warmer days. Then they go back to sleep.

Woodchuck
Woodchuck
Woodchuck (or Grounhog). Photo G D Bebeau.

The Woodchuck, also known as a marmot or groundhog, is a large rodent and great digger that spends most of its life in burrows. In fall woodchucks fatten up on acorns, black walnuts, hickory nuts, chestnuts and other nuts. In October, woodchucks move to solitary winter burrows and block the entrance with soil. They gradually lower their body temperature to just above freezing and slow their heart rate to one beat every six minutes! This allows them to survive the winter on just their stored fat. Woodchucks are considered true hibernators because of their extremely low temperature and heart rate.

Minnesota woodchucks/groundhogs are not likely to wake up as early as February 2 for Groundhog Day, although this may change if springs come earlier and are warmer.

When we return to the Garden in April, some of our feathery and furry friends will not have survived, but thanks to the habitat provided, many will survive and reproduce. The great-horned owls already will be nesting!



Tammy Mercer
Tammy Mercer. Photo Friends of the Wild Flower Garden. Tammy Mercer is a naturalist working part-time for the Eloise Butler Wildflower Garden.

References:
Dunne, Pete. 2006. Pete Dunne’s Essential Field Guide Companion. Houghton Rifling company. New York, NY.

Gill, Frank B. 1999. Ornithology. W. H. Freeman and Company. New York, NY.

Hazard, Evan B. 1982. The Mammals of Minnesota. University of Minnesota Press. Minneapolis, MN.

Heinrich, Bernd. 2003. Winter World: the Ingenuity of Animal Survival. Harper-Collins Publishers, Inc. New York, NY.

Jones, J. Knox Jr. and Elmer C. Birney. 1988. Handbook of Mammals of the North-Central States. University of Minnesota Press. Minneapolis, MN.

Marchland, Peter J. 1987. Life in the Cold: an Introduction to Winter Ecology. University Press of New England. Hanover, NH.

Smith, Susan. 1997. Wild Bird Guides: Black-capped Chickadee. Stackpole Books. Mechanicsburg, PA.

Stokes, Donald and Lillian. 1979, 1983. Guide to Bird Behavior, Volumes One, Two, and Three. Little, Brown and Company. Boston, MA.

Stokes, Donald and Lillian. 1986. A Guide to Animal Tracking and Behavior. Little, Brown and Company. Boston, MA.


Note: This article was published in the Fringed Gentian™, Winter, 2009, Vol. 57 #1. Vol. 57, #1.


Other articles related to birds by Tammy Mercer:

A Great Place for Birding – why the Garden is great for birding, including in May after the Spring migration.

Early Birders Catch the Wonders – what wonders are seen during the year on the Saturday Morning Birding walks.

EBWG as a Migration Rest Stop – an article addressed to the birds about the benefits of Eloise Butler Wildflower Garden as a migration rest stop.

Many Colors of Feathers (The) – about the color of bird feathers and why we see the colors the way we do.

Native Plants - for the Birds – about interactions of plants, insects and bird life. Illustrated.

Rewards of Summer Birding – summer birding and distinguishing fledglings from adults.

Warblers - Spring Warblers and the little time there is to see them. (This is a 1.0mb pdf file)