Winter Survival in Ipswich River Wildlife Sanctuary#
Some Useful and FASCINATING Facts About Winter Survival of Animals Which Inhabit Ipswich River Wildlife Sanctuary
Hibernation#
HIBERNATION is a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and/or lower metabolic rate. Hibernating animals conserve energy, especially during winter when food supplies are limited, tapping energy reserves and body fat, at a slow rate. Although often associated with cold temperatures, the root purpose of hibernation is to conserve energy during a period when sufficient food is scarce. It is the animal’s slowed metabolic rate which leads to a reduction in body temperature and not the other way around.4
Groundhogs and jumping mice#
Groundhogs (also called woodchucks) and jumping mice are the mammals at IRWS which predominantly hibernate for much of the winter. Little brown bats also hibernate, but not at IRWS. They can be found at IRWS beginning in late spring and continuing through early fall. (Reptiles and amphibians also hibernate during the winter, but in cold-blooded animals, this is called brumation.)
Gray Squirrels#
Gray Squirrels construct leaf nests (“dreys”) for protection from the elements, especially where there are fewer available tree cavities. Winter dreys are much more elaborately and solidly constructed than their outward appearance would indicate, with various materials and layers. The inner layer is lined with shredded bark, grass and leaves. It even includes an escape hatch.
Although adult squirrels are usually solitary, they may share nest with their mate for a short time during mating season in winter, or may double up for warmth with other squirrels.1
Red Squirrels#
Red Squirrels harvest cones before they open and bury them by the thousands in the organic soil where the moisture keeps the cone scales tightly closed, preventing loss of seeds. They will locate these stores weeks or months later via a network of tunnels beneath the snowpack.
“During the fall, a red squirrel can often be seen scampering up a tree with a mushroom in its mouth. It seems to understand that it will not last if buried in the soil so it wedges the morsel into the crotch of a high branch (or deposits it in a vacant bird nest!) where the mushroom will air dry and last until it is retrieved.”[quote from 2], 5
Beavers#
Beavers harvest several hundred branches and prop them up in the pond bottom. Some research has shown that the branches are primarily eaten by the kits with the adults living mainly off the stored body fat in their tails.2 They also pack the outside of their lodge to better insulate it. They may need to live under the ice for the entire winter if the pond freezes solid. A hole in the top of the lodge provides fresh air. They remain minimally active during winter and take advantage of the relative warmth of their lodge and huddling lodge mates.2
Muskrats#
Muskrats being much smaller than beavers cannot rely on stored body fat; they need to forage in winter. They feed on plants on the pond bottom. Since their main lodge can be frozen in, they will make feeding shelters they can reach underwater which rise slightly above the water surface so they can get oxygen, like breathing holes made by arctic seals.3,5
Muskrats increase the oxygen stored in their muscles and in their red blood cells by over 42% in winter over the level in summer.
Meadow Voles#
Meadow Voles will stockpile just about any type of plant matter, “usually waiting until snow hides their activity, … then gathering it into larders … more accessible to their communal nests beneath the snowpack.“2
The lowest layer of a snow pack can become a latticework of ice pillars and extensive air spaces, like a continuous snow cave. This subnivian (below the snow) zone is a good insulator, providing living space in addition to the space beneath leaf mold and decaying logs. It also provides some protection from predators.3
Weasels & Mink#
Weasels & Mink are not able to put on much body fat for the winter. As a result, they have to eat more food per day than any other winter-adapted animal.3 They tend to stash excess prey items (primarily meadow vole, white-footed mouse & short-tailed shrew) singly throughout their territories (termed “scatter-hoarding”). Because of the variable snow cover in northeastern Mass. the fur of some short-tailed & long-tailed weasels in this area turn white in winter and some stay brown, an inherited trait of the individual. Mink’s fur remains brown.
Even for those weasels with white fur in winter, the tip of their tail remains conspicuously black. An experiment showed that “… hawks … were confused by the black tip, either momentarily hesitating or attacking the tail as if it were the head end.
Painted & Snapping turtles#
Painted & Snapping turtles hibernate (“brumate”) under the mud in the shallow part of ponds.
The mud is nearly devoid of oxygen so they cannot even use their capacity to take in oxygen through their skin.
In order to survive, they build up oxygen supplies before going into hibernation, and reduce their metabolism to a bare minimum during hibernation. Adaptations of its blood chemistry, brain, heart, and particularly its shell allow the turtle to survive extreme lactic acid buildup while oxygen-deprived.1
Wood frogs & Spring peepers#
Wood frogs & Spring peepers burrow under the leaf litter, and wait for the ice to form.
In one day they undergo a series of chemical changes that make it possible for their bodies to freeze. An antifreeze chemical protects the membranes from freezing, and water is withdrawn from cells by osmosis to restrict ice formation to outside of the cells. 3
Birds#
Birds show an extraordinary ability to quickly add fat during the day in order to keep warm through the night. A few, including jays, chickadees and nuthatches, actively cache food.
“Great-horned owls have been known to cache prey in winter and thaw it by ‘incubating’ it later as they would eggs.” 1
Small overwintering birds in particular use a wide mix of strategies to survive winter, especially at night. They can conserve body heat by fluffing out their feathers to trap air, which has excellent insulating qualities. They also tuck their heads into their feathers to reduce exposed skin surface areas, and blood flow in their feet is reduced to conserve body heat. Some, such as golden-crowned kinglets & goldfinches, tend to huddle together for warmth, particularly at night. They may enter into a state of torpor, or reduced body temperature, when they are inactive at night, but it cannot be too deep, for they must be able to shiver if the external temperature dips too low.3
References#
- (1) What’s That Clump of Leaves?, Art Shomo; W.Va. Wildlife Magazine, winter 2004.
- (2) Nature Guide to the Northern Forest, Peter Marchand, 2010.
- (3) Winter World, Bernd Heinrich, 2003.
- (4) Hibernation, article in Wikipedia.
- (5) A Guide to Nature in Winter, Donald Stokes, 1976.