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Snow, Squirrels, Chickadees and Cubs - UPDATE February 7, 2017

It snowed hard today as is shown in the 1-minute video of a red squirrel on Manny’s bowl at the NABC. Red SquirrelRed Squirrel found a stash of seedsThe squirrel was using its tail to shield its back from the snow. I’d never thought of that use of a squirrel’s tail before. https://youtu.be/6CPlPjiL364

Chickadee waiting patientlyChickadee waiting patiently for its turnOut the window here at the Wildlife Research Institute, as the snow covered the scattered piles of sunflower seed hearts, a red squirrel burrowed to a good stash under the snow. The squirrel left. Black-capped chickadees took note, the only bird species to notice. The seeds were visible from outside. Chickadees streamed to the pile, taking turns. Only one chickadee could be in the hole at once. Some watched for their turn from a perch on a balsam fir branch about 4 feet from the stash. Others perched just outside, waiting for the chickadee in the hole to fly out. Elsewhere, red squirrels uncovered other piles that also became popular.

Chickadee Chickadee Chickadee
Chickadees taking advantage of the squirrel's hard work

 

Somebody asked why black bear cubs are born so small in mid-winter. The black bear schedule for mating and birthing seems to be arranged to maximize opportunities to eat when the eating is good. They mate in late spring and early summer before berries ripen. This is especially important where fall foods are lacking, as here in northeastern Minnesota. If females can’t find enough berries and hazelnuts (a summer nut), they can’t maintain their pregnancies. To avoid having cubs when they would interfere with feeding, they have delayed implantation. The fertilized egg develops only to the blastocyst stage and does not implant in the uterine wall and begin developing into an embryo until November or early December. By that time, the mothers are in dens and have reduced metabolic rates, which means less oxygen consumption. It also means there is no food intake to help nourish embryos in the uterus. Mothers are living off their fat and nourishing their embryos with glycogen from their muscles. Fatty acid molecules are too big to diffuse through the uterus to provide energy for the embryos. There is a limit how much glycogen they can burn up, so they give birth when the cubs weigh only ¾ pound and are smaller, relative to the mother’s size, than any other placental mammal. Outside the mother, the cubs breath on their own, and the mother can make milk for the cubs from fatty acids, conserving her glycogen. This all works out fine and doesn’t prevent the mother from traveling and eating because she is immobile in a den anyway, during the period of scarce food. It isn’t the cold weather that bears are escaping by denning, it is to conserve energy during the winter period when easily digestible foods are scarce to nil. For more, check https://www.bear.org/website/bear-pages/black-bear/reproduction.html.

Thank you for all you do.

Lynn Rogers, Biologist, Wildlife Research Institute and North American Bear Center


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