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Mammals

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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Striped Skunks Seeking Mates

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Striped Skunks are on the prowl, as your nose may have told you recently – males are eagerly seeking out the company of females at this time of year and are often hit by cars traveling at night. The peak of the Striped Skunk breeding season — the third week of March — will soon be upon us. Males will mate with several females in succession and then they often protect their harem against other males by hitting them (other males) with their shoulders or biting their legs. Once a female has been successfully bred, she will not allow further mating activity and will viciously fight any male that attempts it.

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Black Bears Emerging From Hibernation

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Time to take in bird feeders, at least at night. Black Bear sightings are being reported throughout northern New England, a bit earlier than usual probably due to the erratic weather we’ve been having. Adult males emerge from their dens first, females with cubs  last – the opposite order in which they entered in the fall.

Having survived the winter by living off the fat they accumulated last fall, Black Bears weigh considerably less upon waking. Males will typically drop between 15 and 30 percent of their body weight, while lactating mothers can lose up to 40 percent. Even so, for the first two or three weeks following hibernation, bears eat and drink less than they normally do, while their metabolism adjusts to the changes. This is referred to as “walking hibernation” by some biologists. Once normal activity resumes, and until herbaceous green shoots appear in wetlands, bird feeders  are a main attraction.

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An Opossum’s Opposable Thumbs

11-22-16-opossum-hind-foot3-untitled-1Virginia opossums have expanded their range into northern New England, but are still not commonly seen, except, perhaps, lying on roads where they met their demise. There is much to admire about opossums: they are the only North American marsupial, they have more teeth than any other North American land mammal (50) and they possess a prehensile tail and opposable thumbs (both of which are rarities among non-primates).

The recent discovery of a road-killed opossum provided me with an opportunity to examine its feet at close range. An opossum’s front feet have five toes, each bearing a nail. Their hind feet also have five toes, but only four of them have nails. The fifth toe, or “thumb,” lacks a nail and is opposable, allowing opossums to grasp branches and to climb. If you see their tracks, the hind foot is easily discernable from the front due to the fact that the thumb is at a 90-degree angle to the other toes.

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White-tailed Deer Diet In Transition

10-25-16-deer-scat-20161017_5319Even if you didn’t know that a white-tailed deer’s diet changes in the fall, their scat would be a dead giveaway. Its texture and formation are excellent indicators of what a deer has been eating. During the summer, individual pellets are often lumped together due to the moisture content of their summer diet (grasses, clover, alfalfa, apples and other herbaceous food). As winter approaches, deer transition to a diet of twigs, leaves and acorns which results in the formation of individual, dry pellets. At this time of year, it is possible to find both forms of deer scat.

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