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Dens

Red Fox Vixens Preparing Dens

red fox dens4With their breeding season nearly at an end, red fox vixens are preparing for the arrival of a litter of pups in March or April. This involves locating and cleaning several dens, and then choosing one in which to give birth and raise young. An adult female red fox may use the same den year after year; eventually one of her daughters may take it over.

While specific den locations vary, most are on sandy hillsides, often in the woods but close to an open area, and usually there is water within 300 feet or so. A den typically has several entrances, with the main one measuring about ten inches in diameter. At this time of year (if there is snow on the ground) it is relatively easy to locate fox dens, due to soil that has been removed and scattered on the snow.

Vixens often renovate an abandoned woodchuck burrow, but occasionally den underneath an outbuilding, in a hollow log, rock pile or other sheltered area. Pictured are a typical hillside den as well as an abandoned beaver lodge that has been renovated by a fox.  Scat (located about 2 o’clock in the photo) deposited near the entrance of the lodge indicates that this may well be a den that will be used for raising young.

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Porcupines Staying Warm Inside & Outside of Dens

If you’ve ever set eyes on a porcupine den, be it in a hollow tree or rocky ledge, you know that protection from the elements, especially cold temperatures, appears limited. While there is slightly better thermal protection in a rock den as opposed to a hollow tree, neither has any insulation, other than the ever-accumulating bed of scat on the floor of the den, and the entrance is wide open. Even so, porcupines save an average of 16% of their metabolic energy by occupying their dens instead of open terrain, due primarily to the shelter from wind that it provides. In addition, porcupines have two layers of fur which insulate them so efficiently that the outside of their bodies are approximately the same temperature as their surroundings, minimizing heat loss.

Porcupines do venture out of their dens and spend between seven and twelve hours a day outside, without the protection of wooden or rock walls. How can they survive this environment? When outside the den (usually when feeding at night), they are often in conifer stands, and a coniferous habitat provides the same energy savings as a den. Eastern hemlock, which is a preferred winter food, has needles layered so thickly that porcupines don’t lose a great deal of heat to the open sky. The trunks and foliage of hemlocks also re-radiate at night some of the energy they absorb in the day.

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Black Bears In No Hurry to Den This Year

11-16-15 black bear apple scat 026Bountiful acorn and apple crops have enabled black bears to delay denning this fall, as this recently-discovered apple-filled bear scat attests to. Denning is triggered by a seasonal shortage of food, low temperatures, and snow cover on the ground. When these conditions cause bears to den, they typically stay within their summer range boundaries. On average black bears enter their dens in November and emerge in April, but this varies considerably with crop and temperature conditions.

Denning sequence usually begins with yearlings, followed by pregnant females, then solitary females, females with cubs, adult males, and last, subadults (not sexually mature) of both sexes. Most dens are excavated below ground, and on well-drained, upland sites. Rarely are they re-used in consecutive years. Adult males are the first to emerge in the spring, followed by subadult males and females, then females accompanied by yearlings, and finally, females with cubs of the year.

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Porcupines Marking Dens

3-25-15 porcupine den IMG_9681Often, at this time of year, porcupines stake out their den trees (if they’re not inhabiting rocky ledges) by eating patches of inner bark, or cambium, with the exposed fresh inner wood announcing their occupancy. Typically, if a tree den is used year after year, they gnaw off a portion of bark each year, sometimes eating the old, scarred portion which, due to previous chewing, lacks cambium cells, indicating that this behavior is not for the purpose of obtaining nutrients. (photo: porcupine chewing near hollow tree den entrance)

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Black Bear Dens

2-25-15 bear dens1Black bears den in a range of locations, including under logs and stumps, under the branches of a fallen tree, and inside caves and hollow trees. Most adult black bears are not completely protected from the elements while they are hibernating and/or raising cubs, as there is usually a fairly large opening and the bear is exposed to the cold air. The amount of exposure can vary tremendously, from a relatively protected hollow under a log to complete exposure within a dense thicket or stand of conifers. Pictured are two black bear dens where cubs were raised; one is under a fallen tree and the other is in the middle of a stand of spruces.

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Porcupines Entering Winter Dens

porcupine IMG_2597During the summer, porcupines are almost always found out in the open. At the end of October/beginning of November porcupines den up for the winter in the Northeast, with up to a dozen porcupines sharing the same den. While some adult males will spend days at a time in a conifer, most porcupines seek out rocky crevices in which to spend the day, with a smaller number finding shelter in hollow trees. Porcupines are hardy creatures – while dens do protect porcupines from heat loss, they contain no insulation, the entrances are open and the porcupines don’t huddle together for warmth. In addition, porcupines emerge from their dens to feed at night, when outside temperatures are lowest. (And yes, that is porcupine scat that is stuck in/on the porcupine’s quills.)

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Red Foxes Preparing Dens

2-25-14  red fox den 013Red Foxes will be begin giving birth in about a month, so the time for preparing their den has arrived. While it’s never very hard to see a fox den (due to the pile of dirt at its main entrance), they are most obvious now, when the dirt removed by the foxes is conspicuous against the white snow. Red Foxes seldom dig their own den. Rather, they take over a woodchuck’s abandoned burrow, or, in some cases, forcibly drive the woodchuck out (and sometimes devour it, as well). They den in woodlands as well as fields, usually on a sandy knoll where they can observe the surrounding territory, and where their den will be well drained. Most dens have one or two main entrances. The tunnel usually slants downward to about four feet beneath the surface and then extends laterally for 20 to 30 feet and resurfaces. An enlarged chamber along the main tunnel serves as a maternity den.

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