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Black Bears

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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Dung Beetle Feeding on Bear Scat

10-16 dung beetle 127Wherever there is scat, or dung, there are dung beetles. This is a photograph of a dung beetle in heaven as it has located a black bear’s gigantic (apple-filled) scat, which will provide it with food for a long, long time. Some species of dung beetles (rollers) shape pieces into balls and roll them away and bury them to eat later or lay their eggs on. Some species (tunnelers) bury their dung by tunneling underneath the pile of scat. And a third group (dwellers) actually lives inside dung piles.

Most dung beetles prefer the scat of herbivores. There are always bits of food that do not get digested, and these bits are what a dung beetle feeds on. Dung beetle larvae eat the solids, while adult beetles drink the liquids contained in the scat. A given species of dung beetle typically prefers the dung of a certain species or group of animals, and does not touch the dung of any other species.

Dung beetles have a brain that is the size of a grain of rice, yet they are very sophisticated insects. They use celestial clues (the Milky Way) in order to roll balls of dung in a straight line. Dung beetles are known for “dancing,” which helps them orient themselves after their path has been disrupted. They use their dung balls to regulate their temperature, and cool off. (In very warm climates, around noon, when the sun is at its peak, dung beetles will routinely climb atop their dung balls to give their feet a break from the hot ground. Thermal imaging has shown that dung balls are measurably cooler than the surrounding environment, probably because of their moisture content.) And dung beetles keep track of the number of steps they take and the direction from which they came (instead of landmarks) in order to return to their nest with a ball of dung.

Even though they are remarkably clever, dung beetles can be duped! A flowering plant native to South Africa (Ceratocaryum argenteum) produces large, round nuts that are strikingly similar in appearance, smell, and chemical composition to antelope droppings, which the dung beetles accordingly roll away and bury, effectively sowing a new generation of C. argenteum.

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Yellow Jackets Rebuilding Nest

yellow jacket nest2From the size of the chunks of sod that were ripped out of the ground in order to access this subterranean yellow jacket (Vespula sp.) nest, one can deduce that a black bear, not a striped skunk or raccoon, was the nocturnal visitor. Usually there is little intact nest left after a bear tears it apart in an effort to find yellow jacket larvae, but in this case, a portion of the paper nest remained. Apparently undaunted, even with frost in the air (signaling the demise of all the yellow jackets except young, fertilized overwintering queens), the workers lost no time in rebuilding their nest. Twenty-four hours after their nest was torn apart, the colony of yellow jackets had diligently chewed enough wood fiber to have replaced much of it.

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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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Accommodating Both Birds & Bears

3-20 - birds and bears comment IMG_8628In response to my “bears & bird feeders” blog yesterday, a highly respected New England naturalist responded with the following comment, suggesting several ways to have your cake and eat it too. I so endorse his ideas, and especially the reasons behind them, that I am sharing them with my blog readers today.

April to mid- May is perhaps the most food-limited time for birds too. Furthermore, it is my belief that the biggest share of future curious naturalists (and conservationists) are those that grow up in households that feed birds. We NEED those bird feeders out there too! We naturalist types should be thinking about how to bear up and still keep the feeders going. Most of the time, I find that bringing the feeders inside for the night in late afternoon “works”. (I say, like bringing in the cat or the chickens.) We have a “bear resistant” rig here at the Harris Center-a feeding station that is raised and lowered like a flag on a two story flag pole. I know others have found electronic ways of keeping bears away (like motion activated lights), and my friends and neighbors Don and Lilian Stokes are very successful by electrifying their feeding station-just like an apiary. They wish many more people would do so.
Meade Cadot, Naturalist Emeritus, Harris Center for Conservation Education


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