Bear update: voracious appetite and delayed pregnancies By Michael Allen Black Bear Researcher Black bears enter the fall season with a voracious appetite. The urge to feed now will help ensure a successful hibernation. Bears have adapted to surviving the food shortage through winter by remaining inactive in a den for four to six months. To do this, bears will have to spend the rest of their late summer and fall days feeding on berries. It is not uncommon for a 200 lb. adult male to almost double his weight by the time he enters his den in November. This stage in the annual cycle of the bear is called hyperphagia. Calories consumed per day are doubled or even tripled, from 5,000-8,000 to 15,000-20,000. Bears will accomplish this surge in caloric intake by spending up to 22 hours a day feeding on berries. The sugars from these berries will store in the bear’s adipose tissues and will be drawn upon during the winter as fat products. The late valley huckleberry crop this year (about a month behind schedule) has induced an even greater urge for bears to catch up on their foraging. This urgency to feed is reflected in the lower levels of bear-people conflicts in the valley during late July and August. However, depending on the productivity of fall berry crops, traditional complaints of bear activity could return in September and October. For pregnant bears, another change occurs in August. Females, which usually become sexually mature at between four and five years of age, remain in estrus for the entire breeding season of late May to early August or, failing contact with a male, until degeneration of their ovaries. Following mating there is a gestation period of about 220 days. Embryo development stops or is slowed considerably at the blastocyst stage in early to mid-August until the beginning of December, when implantation and development occur for six to eight weeks. Parturition, or birth of the cubs, occurs in late January or early February. Delayed implantation in black bears has improved and adapted the birthing time of cubs. Cubs are born and nursed while the mother is in a state of hibernation for four to five months, between January and May. If delayed implantation did not occur cubs would be born up to three months earlier, increasing the mother’s requirement to draw on her food reserves for a longer period. This year’s survival of the 26 cubs I have identified will depend largely on their consumption of berries from now until denning in October or November. This year’s late berry crop is increasing in productivity and abundance at higher elevations. Currently, eight bear families throughout the valley and on both mountains are foraging heavily on berry-producing shrubs. The table provided lists the shrubs which produce the major berry foods for black bears in the Whistler ecosystem. Dates of ripening are from bear food plots below 800 metres elevation in the Whistler Interpretive Forest, Whistler Valley and Blackcomb Mountain. Berries traditionally ripen first along the valley floor and progress up the mountains through summer. Peak bear use of a berry is often later than at the date of first ripening because bears know it requires less time and energy required to feed when the majority of berry shrubs in an area are ripe. Michael Allen can be heard on Mountain FM’s Mountain Monitor program the fourth Tuesday of each month.
