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Animal Architecture

A Variety of Beaver Lodge Designs

10-20-14 beaver bank den 080Beavers are hard at work refurbishing their mud and stick lodges in preparation for the coming winter, when their movements will be restricted and they will spend both days and nights inside their lodge. When we think of a beaver lodge, we picture it in the middle of a beaver pond. This was not always the case, however, and still isn’t today. The earliest and most primitive beaver lodges consisted of a burrow in the side of a high bank with the entrance under water (see exposed bank lodge entrance in photo insert). The next advance was the addition of sticks and mud piled over the top of the bank as added protection from predators (see photo). Eventually beavers started building a complete lodge on top of the bank which had an underwater entrance. The most advanced design is the lodge we most commonly associate with beavers — one that is built up from the bottom of the pond and is completely surrounded by water. It requires the greatest amount of work but offers the greatest amount of protection to the beaver.

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Signs Of An Active Beaver Pond

4-7-14  floating beaver logs IMG_0159Beaver ponds have finally started to melt, making it easy to determine whether or not there have been beavers living in any existing lodges over the winter. The tell-tale sign is floating de-barked sticks and branches. During the winter, beavers leave their lodge and swim out to their underwater food supply pile and haul branches back into the lodge where they chew them into foot-long pieces for easy handling. The bark is removed and eaten as the beaver holds the stick and turns it, much as we consume corn on the cob. When little or no bark remains, the stick is discarded out in the open water. These sticks remain hidden underneath the ice on the surface of the water until warm weather arrives and the ice begins to melt. At this point the sticks and branches become visible, and often extend several feet out from the lodge. These sticks will not go to waste, but will be used for dam and lodge repairs. (Photo taken standing on lodge.)

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A New Book for Budding Naturalists

COVER-BeaversBusyIs there a youngster in your life who might love his or her own book about beavers? My third children’s nature book, The Beavers’ Busy Year, has just been released. Having been an ardent admirer of this rodent for many, many years, it is gratifying to have had a chance to instill a love for beavers in youngsters age 3-8 with this non-fiction book. The adaptations of beavers’ noses, eyes, ears, fur, feet and tails are highlighted in the text and photographs take the reader through the seasons of the year from a beaver’s perspective. Activities at the end of the book engage children in matching photographs of various beaver signs such as tracks, scent mounds and incisor marks with written descriptions. There are also activity/informational sections on beaver tails, beavers as engineers and creators of habitat for other wildlife, and dam building. It should be available at your local bookstore, but if not, I’d greatly appreciate your letting them know about it. Thank you!


Winter Mouse House

2-5-14 mouse nest with insulation roof IMG_4629White-footed Mice and Deer Mice are known for their keen ability to recognize a potential winter home when they see it. Abandoned bird nests provide firm foundations, and more often than not, mice will create an insulated roof made out of thistle down or milkweed fluff when renovating a nest. There are exceptions to this rule, however. If you look closely you’ll see that the roof of this nest has a slightly greenish tint, the reason being that the roofing material selected was none other than green insulation “borrowed” from a nearby human dwelling. (Thanks to Heidi Marcotte and Tom Wetmore for photo op.)

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Beaver Breath

12-2-13 beaver breath  074It’s very subtle, but in winter, especially when it is very cold outside, there is a way to tell if a beaver lodge is occupied. The temperature inside the lodge remains relatively stable at around 34 degrees Fahrenheit. When snow falls, it provides added insulation, raising the interior temperature of the lodge slightly. A layer of fat and thick fur keep beavers warmer than the air inside the lodge, plus they raise their body temperature even more by sleeping piled on top of one another. All the moist, warm air that beavers give off through breathing and evaporation escapes through the (mudless) vent that goes up through the center of the roof of the lodge to its apex. The vent’s purpose is the exchange of air; when the warm air inside the lodge rises and hits the cold air outside the lodge, it condenses and forms water vapor that is visible, indicating that there is life inside.

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Cecropia Moths Pupating

11-11-13 cecropia cocoon dissected  056Our largest North American native moth, the Cecropia Moth, Hyalophora cecropia, spends the winter as a pupa inside a cleverly-crafted 3” – 4”-long shelter, or cocoon, which it creates and attaches lengthwise to a branch while still in its larval stage. The Cecropia caterpillar, with the silk glands located near its mouthparts, spins not one, but two silk cases, one inside the other. In between the two cases, it spins many loose strands of very soft silk, presumably to enhance the insulating properties of the cocoon. Inside the inner case, the caterpillar splits its skin and transforms into a pupa. Come spring, an adult moth will emerge from the pupal case and exit the cocoon through one end which was intentionally spun more loosely, allowing the moth to crawl out the somewhat flexible tip. (Note: dissected cocoon was not viable.)

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Ribbed Pine Borer’s Winter Pupal Chamber

11-6-13  ribbed pine borer winter shelter 132The larva of the Ribbed Pine Borer, Rhagium inquisitor, (a beetle) lives just under the inside of a pine tree’s bark. It is a long-horned beetle, and in the fall, when it’s ready to pupate, it creates an oval cell by chewing a relatively flat chamber approximately 1 ¼” long. The Ribbed Pine Borer uses the woody fibers it chewed to form a raised “wall” surrounding the chamber. It then pupates inside the wall, and overwinters in the chamber as an adult beetle, emerging to mate in the spring. (Thanks to Kitty Stanley for photo op.)

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