Growing Bears in New Mexico

Vocabulary: adaptation, cavity, camouflage, competitor, circumference, dormancy, digitigrade, embryo, habitat, hibernation, herbivore, omnivore, navigate, plantigrade, stationary, torpor

Background Information – Black Bear Biology:

Note: A more condensed summary is the Wildlife Note: Black Bear.

People who live in New Mexico are lucky to share their forests with black bears (Ursus americanus). Bears are generally very wild, secretive animals that will run away if they see you. If they become food-conditioned and associate people with food they can become a nuisances. This happens when people carelessly leave garbage, pet food, or bird feeders accessible to bears. If a bear loses its fear of humans in this situation, it often loses its life because it must be killed before it hurts someone.

New Mexico’s black bears are creatures of the forest. Camouflaged by its brown or black fur, a black bear easily fades into the shadows. It can move quietly on its soft, broad foot pads. Bears walk on their feet as humans do, with their soles flat on the ground-this is called plantigrade. Most other mammals, such as cats or dogs, walk on their toes-this is called digitigrade. Black bear tracks are about 8 inches long and have a curved line at the front of the front pad. Being able to navigate the forest quietly and unseen helps a bear avoid other bears as it searches for food. If a young bear accidentally runs into a large adult male, who could consider the youngster a competitor, the younger animal needs to retreat before it is discovered. Male black bears will occasionally kill and eat other males in their home range! If necessary, bears can run 30-40 miles an hour for short distances or paddle across a lake.

Bears become adults around 3-4 years of age and depending on their age and size they can mate in May and June.  Although bears mate in the spring, cubs are not born until the following winter.  Female bears that are expecting cubs use their stored body fat to grow the developing embryos.  She gives birth in the den to an average of two cubs every other year (at the most).  Cubs are born in late January or early February. The cubs are helpless when born, their eyes are closed, and their thin fur is not enough to keep them warm. On average they weigh 8 ounces.  For humans an 8-pound baby at birth is about 7 percent of the weight of a 120-pound mother.  A newborn bear cub is just a fraction of 1 percent of the mother bear’s weight!  When a cub greets the outside world in late April or early May, it weighs 4 to 10 pounds and is usually strong enough to climb trees. They eat some solid foods but they depend on mother’s milk throughout the summer to help it grow strong and ready for winter hibernation. At the end of their first year they weigh an average of 40-45 pounds. Cubs usually den with their mother the first year.

Bears in New Mexico begin to enter dens by October 15, and a few bears do not enter dens until after December 1st. In the spring, most bears are out between April 1 and May 1. In general, female bears enter dens earlier and emerge later than males.

Black bears either dig out their dens or use natural openings such as hollow logs, tree cavities, holes dug into hillsides or under rocks or boulders, or under the base of stumps, trees, or logs.  Bears will also use human-made structures such as drainage culverts, and basements or foundations of buildings.  Most dens, are surrounded by dense vegetation which helps hide the entrance. Females seem to prefer tree cavity dens when they are available.

Most bears build nests within their dens.  Nests are built out of nearby plant materials (vegetation) such as pine needles, twigs, leaves, and grass.  Most all bear dens are reused in following winters. Dens are most common in mixed conifer and spruce fir habitats in New Mexico but are also found in ponderosa pine forests and piñon -juniper woodlands.

(For more in depth information on black bears in New Mexico please see [wpfilebase tag=file id=1895 tpl=filebrowser /], by New Mexico Department of Game and Fish).