Incredible Creatures
Prior to European settlement, the grizzly bear (Ursus arctos) called much of California home. Today, despite appearing on the California state flag, the grizzly is extinct throughout the state; the last known California grizzly was killed close to Sequoia National Park in 1922. The savvy Sierran black bear population (Ursus americanus), however, is still thriving.
Size
Size can vary dramatically between black bears. By adulthood, males usually range from 150 to 400 pounds (70 to 180 kg), and females from 90 to perhaps 300 pounds (40 to 135 kg). Males gain weight until they are ten years old or more, while after three years females grow only slowly and stop after seven. Differences in size are indistinct until puberty, at which point females redirect nutrition from growth to reproduction.
Male bears lose weight rapidly through the spring and then gain weight from July until denning in the fall. This seasonal weight change may be explained by mating behavior – male bears expend substantial energy visiting the home ranges of eligible females at a time when food resources are at their lowest. Conversely, female bears are at their lowest weight upon emergence from the den and gain steadily through the year. Females, however, do pay a substantial weight penalty for reproduction; sows with young are 15% lighter than cubless females and may gain only a fourth as much weight from May to September.
Color
Despite their name, black bears range in color from blond through various shades of brown to black. About 95% of bears in the Sierra are some shade of brown and only about 5% are truly black. Color changes through the year are common in bears. Guard hairs start bleaching immediately after the molt, which occurs sometime between May and September. Molting is signaled by the appearance of new guard hairs, which are shorter and darker. They first emerge around the eyes and lower limbs, and then extend up the limbs and down the face and flanks, finishing along the spine.
Lifespan
Longevity for bears in the Sierra varies, but the average lifespan is 18 years. The most common causes of death include accidents with vehicles, disease, enemies, old age, and starvation due to loss of functional teeth.
Communication
Black bears communicate through posturing, marking with odors or other sign, and vocalization. Unlike dogs that can display teeth or curl a lip, a bear’s ability to communicate with facial expressions is poor. The most significant and productive act of communicating for a bear is through its body posture. Bears are often seen in movies and television standing on their two hind legs, growling and looking quite ferocious. In real life however, black bears “stand up” when they are trying to get a better look or smell at something that has piqued their curiosity, and growling is rarely a sound that you will hear from a black bear. When bears assess other bears, staring, slapping the ground, and bluff charging are aggressive behaviors, while lowering the head is submissive. To mark a tree, bears will rub the trunk with their shoulder, neck, and rump. They claw and bite bark and roll on the ground at the base of trees as well.
Although bears are generally silent animals, they do have several vocalizations:
- Huffing: a single rapid, highly audible exhalation of air through the open lips, produced by both cubs and adults.
- In-Out Huffing: rapid inhalation and exhalation similar to single huffing repeated rapidly.
- Bawling: a long hoarse wailing sound produced by cubs.
- Grunting: a soft “clungk, clungk” made deep in the throat with the mouth closed. Produced by mothers in the presence of cubs.
- Jaw-Popping: a rapid snapping of the jaws and popping of the lips, produced by all bears.
- Tooth-Clicking: the jaws are snapped together two or three times, more softly than jaw-popping. This is another sound produced by mothers with cubs.
- Moaning: a falling note from deep in the throat, much like a human moans, and produced by all bears.
Grunting and tooth clicking seem to be the sounds with the most specific intentions and are almost exclusively used by mother bears with cubs. Grunting seems to mean, “come here” and tooth-clicking is usually followed by the cubs climbing trees. Bawling is done by cubs separated from their mothers, while huffing and jaw-popping often precede or follow bluff charges. This behavior is usually used by animals on the defensive and is used as an alternative to physical contact. In-out huffing is commonly used by bears climbing trees to escape a nearby threat and is a “last ditch” response while fleeing. Bears that are kept in trees for long periods often moan, perhaps implying resignation or defeat.
Reproduction
Female black bears in the Sierra Nevada are usually between three to five years of age when they have their first litter. Courtship and mating usually takes place in a two or three week period in June, July and sometimes as late as August. Bears are polygamous, and a single male may mate with several females. The gestation period for black bears is 235 days (about 8 months), but embryonic growth only takes about two months. This is because bears have a unique reproduction system called embryonic delay, or delayed implantation. Although mating takes place in the summer, the fertilized ovum does not implant for many months. Because of this, bears are only able to give birth when they are in good condition. If the sow has not gained enough weight to support herself and her cubs during the winter, she will abort, and the blastocyst is absorbed by her body.
If a sow is healthy enough, she will give birth during hibernation inside the den in late January or February. Average litter size is two cubs; however, three cubs are not uncommon in the Sierra Nevada. Cubs weigh about 8 ounces at birth and grow to approximately 10 to 12 pounds by the time they leave the den three months later. The cubs will stay with their mother for the rest of the year and will den with her the next winter. After emerging from the den the second year, they will stay as a family unit until the sow is ready to mate again in early summer.
Temperature Regulation:
Like humans, a black bear’s normal body temperature is around ninety-eight to ninety-nine degrees Fahrenheit (though it can vary during hibernation). A black bear’s thick fur serves as excellent insulation during the cold winter months, but it can be problematic in warm weather. Bears, like dogs, do not have sweat glands. Because of this, they must cool themselves through other means:
- Balancing energy expenditure and food intake
- Resting in shady day beds
- Lying with their bellies fully touching the cool ground
- Panting
- Submerging themselves in water