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Bears beefing up

"Younger bears have now evolved non-natural food-seeking behaviours further by breaking into buildings."



Michael Allen

Naturalist and Bear Guide

Whistler black bears experience two major shifts in their annual biology during mid-summer in early August – the end of the breeding period and the start of hyperphagia or hyper-feeding.

The breeding season typically runs from late May through late July when adult males (> 3 years) search for single (barren) adult females (> 2 years) for courtship and subsequent copulation. The earliest a courting pair of mature adults was observed was on May 23 (earliest since 1994 was May 17). For the first time, I never observed breeding activity during July. The peak of mating seems to be the last week of May and the first three weeks of June.

Because females with cubs-of-this-year (2006) skip their first spring's breeding period, some males may attempt to kill cubs to force the mother back into estrous. Three mothers lost four cubs to aggressive males during June. One mother lost her entire litter of two cubs over a three-week period and each of the second and third mothers lost one cub but continued to raise the remaining cub.

The cooler spring seemed to give most bears good forage throughout ski trails, golf courses, and valley greenbelt. Bears grazed on easily digested, new green vegetation from late April through late July. In early July, bears expand their diet to include high sources of protein. Carpenter ants (and larva) are consumed from rotten logs and tree stumps. Honeycomb and larva from bee nests and hives are also consumed.

Garbage continues to be a problem in Whistler Valley as bears gain access to non-natural foods each week since May 1. The trend during the last seven years in garbage-seeking behaviours by younger bears ( < 7 years) is evident; the bears have been rewarded and bears have now evolved non-natural food-seeking behaviours further by breaking into buildings. It almost seems as if bears are utilizing residential areas as if they were campgrounds, each house representing a campsite. It's ironic that we bear proof campgrounds in parks but we do not provide bear proof containment in residential areas. What's the difference?

The cooler spring did push berry ripening back 1-3 weeks. Valley berries began ripening in early July but berry abundance was scattered. And due to the subsequent hot weather in July berries remain small and began shrivelling earlier. Currently, bears are foraging a moderately abundant berry crop below 1,000 metres elevation.

The breeding period is officially over (by August) and bears begin experiencing the next hormonal shift, which triggers hyperphagia or hyper-feeding. From August to October bears will increase daily activity to over 15 hours a day as they forage huckleberries and blueberries and mountain ash berries. Bears have three months to fatten up for six months of winter hibernation when natural foods are unavailable.

As of early August the high elevation berry crop (> 1,200-metres) looks good with large, green berries. The next two weeks should see continued ripening of berries pulling bears from lower elevations. Balanced weather (precipitation and sunshine) during August will help maintain a consistent berry crop through September.

Despite a good forecast, however, all bears do not gain access to berries equally. Younger bears will be pushed out of prime feeding areas until most berries are depleted and will typically rely on late berries in the valley and continued access to available human foods.

Shortly after hyperphagia begins, at least seven (observed breeding) adult females will be suspending two (range 1-5 eggs) fertilized eggs from implanting in their uterine walls until late November. This process, called delayed implantation, prevents the birth of unhealthy cubs (and unnecessary physiological strain on the hibernating female) by allowing adult females to add the necessary weight during three months of berry feeding so that their "bodies" can make the decision to implant the free-floating eggs during early December. If sufficient weight is gained, eggs implant and about 45 days of fetal development will allow the birth of cubs between mid-January and early February.

If sufficient weight is not gained, eggs are reabsorbed. If marginal weight is gained, then litter size is limited to one cub. Dominant bears usually gain the most weight (70-170 lbs.) during the three-month berry season.

If you want to learn about more female bear biology from my observations over the last 13 years, come to MY Place on Aug. 26 for The Biology of Female Bears, a presentation sponsored by the Whistler Museum and Archives Society.

Thanks to Pique Newsmagazine for continued support of this column.