An online resource based on the award-winning nature guide

Mammals

Black Bears Foraging

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This is the time of year when Black Bears are looking for every available source of food in order to bulk up before entering hibernation. During this period of gorging (hyperphagia) Black Bears consume large quantities of fruits, berries, nuts, grasses, roots and insects.

In particular, they favor the brood (larvae and pupae) of ants, due to their relatively high content of fat and protein. Black Bears find brood by detecting the pheromones and other chemicals such as formic acid that ants use for communication and defense. Research has confirmed that Black Bears will dig up as many as 200 ant colonies a day, flipping rocks, moss and leaf litter over and tearing apart logs, stumps and snags (such as the one pictured), using their canine teeth and claws to gain access to the ants. Once they have torn apart the stump or snag, they use their long, sticky tongues to gather brood. Anthills are avoided except for when Black Bears are extremely hungry, due to the fact that bears prefer not to get a lot of soil or sand mixed in with the brood they’re eating. (Thanks to Virginia Barlow for photo op.)

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The Varied Diet of Muskrats

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Muskrats are primarily herbivorous. The majority of their diet consists of the tubers, roots, stems, leaves and fruit of a variety of aquatic and terrestrial plants, particularly those of bulrush, cattail and arrowhead. A diet of high fiber is possible because of bacterial fermentation which takes place in their intestines. The digestion of many herbivores is aided by bacteria, but many plant-eaters are restricted in what they can eat because they are unable to change their diet without killing the bacteria. Muskrats, however, can and do consume large amounts of meat (frogs, fish, turtles, crayfish, etc.) and still maintain a healthy population of fiber-digesting bacteria. (Thanks to Jeannie Killam for photo op.)


Black Bears Communicating

6-21-17 black bear by Alfred 2017-05-24 15.35.19Black Bear males are not shy about making their availability and intentions known to the opposite sex. Their most prevalent means of communicating this information is to leave their scent on trees (as well as other structures, such as telephone poles– see photo) by scratching them with their claws, biting them and rubbing on them with their shoulders, back and neck. Often they will use the same marking tree year after year, with signs accumulating on the tree.

Both males and females mark trees year-round, but at this time of year, at the peak of their mating season, males are especially active markers, in order to convey their social identity, reproductive status and location to female passersby. One might consider such marking trees as ancient “scratch.com” mating sites. If you find one, be sure to look for stray hairs that have been inadvertently left behind. (photo by Alfred Balch)

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Muskrats Busy Feeding Young

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Birthing time for Muskrats is late April/early May, so this year’s young are roughly a month old. Weaning begins now and young Muskrats, who have been able to swim since they were two weeks old, begin foraging for themselves. Parents continue to supplement their offspring’s diet during this transition.  Although Muskrats are omnivores, the majority of their diet consists of the roots, stems, leaves and fruits of aquatic vegetation. However, when you’re feeding half a dozen offspring, you harvest whatever is available, including bedstraw (see photo).

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This Year’s Black Bear Cubs Growing Up Fast

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It’s hard to believe that four months ago when it was born this Black Bear cub weighed less than a pound and measured about eight inches in length! Most Black Bears mate in June, but because of delayed implantation their fertilized eggs don’t implant in the uterine wall and the embryos don’t begin developing until the fall (if the mother has had a sufficiently nutritional diet), just as the mother is entering hibernation.

The cubs are born in January, after only a few months inside their mother. They are just a fraction of one percent of the mother bear’s weight, compared to an average human baby that is about seven percent of its mother’s weight. The cubs nurse constantly for the next four months (during which time their mother is not eating or drinking).  The fat content of Black Bear milk can be as high as 20-25 percent. Human milk is comparable to cows’ milk, generally ranging between three and five percent fat. (A biologist who had the opportunity to sample Black Bear milk reported that it was similar in taste to sweetened condensed milk.)

In April, when the cubs emerge from their den, they weigh about six pounds.  Milk production and intake now increases four-fold. Peak lactation (45 ounces of milk per day per cub) occurs in June and July. As a result, the cubs have a huge growth spurt their first summer and will weigh between 40 and 60 pounds by the end of it.

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Red Foxes Giving Birth

3-22-17 red fox kit IMG_7433Red Fox vixens are giving birth to one to seven pups (usually three to five) in their underground dens at this time of year. The pictured pup is about four weeks old, and is starting to acquire its sand-colored coat. Red Fox pups are born with a temporary coat of dark grey-brown fur which we rarely see, as they stay in their den for the first month or so, where their mother provides warmth and milk.  At the age of four weeks or thereabouts, the pups begin to emerge from the den and sit, nap and play near its entrance. At that time they grow a second coat that is very close to the color of the sandy terrain in which their den is usually dug. Their red coat, for which they are named, develops later in the summer.

Although it’s too early to see Red Fox pups, keep an eye out for active dens which are easiest to find where there is still snow on the ground, as the dirt around the entrance is usually visible. Males can sometimes be seen going back and forth, delivering food to the vixen and her pups.

The next Naturally Curious post will be 3/24/17.

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Eastern Chipmunks Emerging & Mating

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All winter long, Eastern Chipmunks have been intermittently napping and running to their underground larder to snack every week or two. As spring approaches, the timing of their emergence above ground is affected by the weather, even though their tunnels are 18” – 36” below the surface. Within the last week chipmunks have been seen above ground.  One would think they must be in a state of confusion, given the erratic weather we’ve experienced this spring.

Chipmunks waste no time once they are active.  Most adult females are in breeding condition when they emerge (as opposed to males, which are in a state of constant readiness) and mate within a week. This involves 10-30 couplings within about a 6-7 hour receptive period.  In a month or so, the results of these efforts will be born.

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