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Posts tagged “Ursus americanus

Black Bears Gorging

10-28-16-corn-203Black bears are omnivores as well as opportunists.  They will eat almost anything that they can find, but the majority of their diet consists of grasses, roots, berries, nuts and insects (particularly the larvae).  As the days cool, and the time for hibernation nears, black bears enter a stage called “hyperphagia,” which literally means “excessive eating.”  They forage practically non-stop — up to 20 hours a day, building up fat reserves for hibernation, increasing their body weight up to 100% in some extreme cases.  Their daily food intake goes from 8,000 to 15-20,000 calories. Occasionally their eyes are bigger than their stomachs, and all that they’ve eaten comes back up.  Pictured is the aftermath of a Black Bear’s orgy in a cornfield.

If you  share a bear’s territory, be forewarned that they have excellent memories, especially for food sources.  Be sure not to leave food scraps or pet food outside and either delay feeding birds until bears are hibernating (late December would be safe most years) or take your feeders in at night.

NOTE:  Orders for 2017 Naturally Curious calendars must be received by October 31.

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Black Bear Lactation

2-11-16  black bears IMG_0380Black Bear cubs are born in late January or February, weighing about eight ounces. The newborn cub(s) immediately crawl to their mother’s teats (she has six) closest to her pelvis to nurse. Later, as the cubs get older, they nurse from the top four and the mother often “switches off” production in the bottom two. At birth a Black Bear cub weighs half to three-quarters of a pound, and when it emerges from the den in April it averages about six pounds.

Most hibernating mammals are not pregnant. The fact that Black Bear cubs are born in late January or February, and the mother bear nurses them for two or three months while she is not eating or drinking is a phenomenon in and of itself – just ask any ravenous nursing human mother.

Milk production and intake increases four-fold after the cubs emerge from the den. At peak lactation (June and July) a black bear cub consumes about 30 ounces of milk a day. If a bear has two or three cubs, that means she must produce two or three quarts of milk a day. The milk of Black Bears is very rich: human (and cow) milk is about three to five percent fat while Black Bear milk is around 20 to 25 percent fat. In addition, the carbohydrate composition of the Black Bear mother’s milk while she is nursing in the den is relatively high compared to the carbohydrate composition found in milk after denning; the protein content after denning is double that of milk produced during hibernation.  At roughly six to eight months of age, Black Bear cubs are weaned. (Thanks to Ben Kilham for photo op.)

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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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Black Bears Seeking Protein

9-2 hornet nest torn by bear 083Although insects and animal matter make up less than 10% of the annual black bear diet, they are a crucial part of it. Black bears get most of their animal protein from ant brood, hornet larvae, tent caterpillars, march fly larvae, grubs (especially June beetle grubs), and snow fleas. Among the most preferred sources are bee and hornet larvae. Berries and other fruit don’t have a great amount of protein, but they do have some (blackberries = 2 grams of protein per cup). If the summer berry crops fail, insect brood is especially important, especially at this time of year, when bears are seeking protein, fats and carbohydrates, putting on as much as 30 pounds per week to sustain themselves through the coming months of hibernation.

When tearing apart a beehive, yellow jacket nest or bald-faced hornet nest (see photo), bears do get stung, particularly on their ears and faces (their fur is fairly impenetrable). Apparently the reward is worth the aggravation. After filling themselves with brood (and in some cases, honey) black bears shake vigorously in order to rid themselves of any insects that are caught in their fur.(Thanks to Alfred Balch for photo op.)

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Black Bears Marking Territory & Mating

6-30 black bear sign 032Black Bear (Ursus americanus) breeding season begins in May and lasts until early July, with mating occurring mainly during June. The female traverses her territory at three times her normal rate during this time, laying down a scent trail which the male follows. Both male and female periodically intentionally deposit their scent by straddling vegetation, breaking off small limbs and biting, scratching and rubbing on trees (and telephone poles if available). Tree species often used for marking include White Birch, Balsam Fir, Striped Maple and Red Pine. When contact between the bears is eventually made, they nuzzle and chew on each other’s head and neck and may even wrestle a little. Mating occurs repeatedly for several days. (Thanks to Alfred Balch for photo op.)

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Black Bear Yearlings Soon To Be On Their Own

5-19-15  black bears 067Female Black Bears become sexually mature at three-and-a-half years of age. They breed in June and give birth in January or February (delayed implantation). Black Bears have a 2-year reproduction cycle: the cubs remain in the custody of their mother for roughly a year and a half, during which time the mother doesn’t mate. In May or June of the year following their birth, when they are 16 or 17 months old, the yearlings become independent and go off on their own — – just prior to black bear mating season. (Thanks to Jill and Bryan Marquard for photo op.)

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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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