Bear By William M. Williams A FEMALE black bear stirs just long enough to give birth to her cubs in the darkness of an excavated den. Weighing no more than a can of soda and covered in fine black fur, one cub cries out as a storm rages outside. The newborn bear, only 9 inches long, has rudimentary ear buds and will not open its eyes for another six weeks. An innate ability to seek out heat stimulates it to crawl clumsily toward the sow's breast where it begins to nurse. Two littermates follow and join in the feeding. Scenes such as this play out unseen under the frozen landscape of Pennsylvania throughout much of January. Nature's Way Nature sees that bear cubs are given an optimal chance of survival. Female black bears breed every two years, with the peak 28 NORTHEAST REGION Information & Education Supervisor of mating season taking place from midJune through mid-July when dominant males search for receptive sows. Males fight one another for the opportunity to breed and many will mate with multiple females. While eggs are fertilized immediately, only tiny balls of cells called "blastocysts" will develop initially. These bear embryos are about the size of pinheads and will float freely in the sow's uterus for the next several months without any further development. Changes in the amount of daylight during late October and early November trigger hormonal changes in the sow, causing the blastocysts to finally attach to the uterine wall and embryonic growth to resume. Scientists call the process delayed implantation, and it is a reproductive strategy used by only a few species, most