Black Bear tracks - Ursus americanus
This week there were Black Bear tracks in the snow! Most people think that bears aren't active at all in the winter. They believe that hibernating bears go to sleep in the fall and don't wake up until spring. That's probably true in areas where winter is harsh, temperatures are below freezing, and the snow is deep. Where we live, winter isn't that long or severe, and bears can be active during periods of "warm" weather, and then go back to sleep if snow and cold temperatures return.
Hibernation
Hibernation is a complicated process in mammals. The level of hibernation varies between species. Yellow-bellied Marmots do truly hibernate, whereas Black Bears don't. I found the following summary of Black Bear hibernation at www.denali.org/denalis-natural-history/black-bear-hibernation/.
"Hibernation is the mechanism that black bears use to conserve energy and reduce their internal fires of metabolism. For a long time people thought that the bears slept through the winter in cozy dens and emerged in the spring fully charged.
However, far from being a long, uninterrupted sleep, hibernation consists of periods of sleep punctuated by periods of arousal. Sleep time is long during the dead of winter but is shorter at the beginning and end of the season. To prepare for this long season black bears feed ravenously from midsummer through the end of autumn, gleaning up to 20 thousand calories in a day. Bears are omnivores and will eat meat too, including ground squirrels, carrion and whatever they can find. By the end of autumn, a black bear will have added about 4 or 5 inches of body fat and more than doubled the insulation provided by its pelt.
As the bear enters hibernation, its metabolic processes such as body temperature, heart rate, and respiratory rate are reduced. But bears do not lower the body temperature as much as once thought. Their hibernation temperature is around 88 degrees and waking temperature is 100 degrees F. This relatively high sleeping temperature allows black bears to become fully alert if aroused, perhaps to enable the bear to protect itself from predators and other dangers without unnecessarily taxing their energy reserves. Over the course of a hibernating season it is thought that black bears use approximately 4,000 calories a day, which results in a weight loss of about 20 percent of it body weight by spring."
Ladybird Beetles - Hippodamia convergens
Diapause
The cold temperatures have put a stop to insect movement for now. They cannot regulate their body temperature, like birds and mammals. Once temperatures drop into the 30's, insects become immobile. To keep from freezing, most adult insects reduce the amount of water in their body fluids by 30%, and replace it with glycerol, sorbitol, or other types of anti-freeze. As temperatures begin to drop they enter a state of diapause, similar to hibernation in mammals, in which they become inactive and their metabolic and respiratory rates slow down.
Another way insects deal with winter, is that the adults will die off and leave their eggs or larvae to overwinter in water, underground, or under cover of leaves, bark or protected crevices.
Ladybird Beetles - Hippodamia convergens
In the fall, Ladybird Beetles converge in large numbers in our neighborhood. They don't converge because of "safety in numbers", but rather to mate before winter sets in. They are very visible, but aren't eaten by birds as apparently they are unpalatable to the birds!
Ladybird Beetles - Hippodamia convergens
If you find a group of Ladybird Beetles on the trunk of a tree, look in the leaf litter at the base of the tree and you'll probably find lots more of them!
Dormancy
Once again icicles are hanging from some of the mosses in our neighborhood! The reason why the moss itself doesn't freeze, is that during winter moss, like insects, has a natural anti-freeze (glycerol, sucrose etc.) in its cells! This lowers the temperature at which water freezes, so the plant cells aren't frozen and damaged.
Lots of plants use this anti-freeze technique to survive the winter, including most evergreen shrubs and trees, some ferns, succulents, and liverworts! Additionally, many plants go dormant in the winter, and enter into a state of temporary metabolic inactivity or minimal activity.
Fir Cap - 1/19/23
Local Weather
This week the heavy rains stopped and we had one last storm that left two inches of snow on the ground in our neighborhood. The total precipitation for the week was 4.06". The forecast for the coming week is sunny with cold nights. I'm grateful for a break in all that rainy weather!
Higher up there is a lot more snow! The latest news I've heard is that there is 8' of snow at Yuba Pass, and about 4' of snow up in the Lakes Basin! I'll have to get up there this week and check it out!
Hairy Woodpecker - Dryobates villosus
Are there any woodpeckers around?
What's happening in the foothills?
Check back next week for the answers to these questions and more!
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