Wildlife adapts to winter’s chill

Winter is not yet upon us but the flora and fauna of the Okanagan have begun preparations for the months of cold that lie ahead. Like some of us, many of our birds
cope with winter by flying south and avoiding it altogether. This is no trivial feat, involving, as it does, the laying on of energy stores in the form of fat and deploying a complex map and navigation system. Depending on the species –the sun, the stars, the earth’s magnetic field, and learned landmarks may be involved in charting the southward course by our feathered friends. So think twice before attempting to insult someone by calling them “bird-brained”- there’s a pretty sophisticated GPS under those feathery caps.
In perhaps an even more impressive feat, monarch butterflies carry out a migratory achievement on par with most birds, equipped with a brain for which the epithet “pinhead” would be a compliment.

In a sense the complexity of migration is a testimony of sorts to the difficulty of enduring our winters. Our bears pass the winter in a somnolent state with a body temperature lowered from about 38 C to around 31 C. They’re considered “shallow hibernators”. The lower temperature is easier to maintain and saves precious calories. The truly remarkable thing about bears is that they are able to pass the entire winter in this state without ever needing to eat, drink, urinate or defecate. Besides this enviable achievement lady bears are able to give birth to and suckle their cubs. Smaller animals such as ground squirrels, marmots and jumping mice face a different situation - it’s cheap to warm up their small bodies but hard to keep from losing heat to their surroundings. As a result their core body temperature hovers just a few degrees above freezing-typically 6-to 4 C. Unlike bears they re-warm periodically to defecate, urinate and re-grow brain cell processes among other chores. Their brains stay a bit warmer than their extremities, and if the burrow temperature should drop below zero they are able to sense it, and elevate their metabolism to stay above the freezing threshold.

For some cold blooded vertebrates, and for countless insects and plants, zero degrees holds no terror. By judicious super-cooling, and liberal production of organic antifreezes, they are able to prevent water from freezing at temperatures well below zero. This is the same trick employed by our familiar orchard trees and it works, down to a limit of nearly -40 C, by excluding any substances that can “nucleate” or initiate ice formation.

Ice within the cells of living things is lethal. Its expansion disrupts and destroys their structure, resulting in death if vital organs are afflicted. The most impressive strategy of coping with extreme cold is not by avoiding freezing but by controlling it. This means directing freezing to spaces between the cells, which are simultaneously dehydrated without deactivating the proteins and other vital components within them. Our hardiest trees and shrubs, and most famously among animals - the wood frog - have mastered this near miraculous feat of natural nanotechnology. The body of this rather ordinary looking amphibian becomes about 65% solid ice when the weather turns chilly. Something to think about while snuggled up to the fire.

Dennis St John
Nature Wise