Resident black bears experienced a wave of relief as recent sunny days and warmer nights (since Sept. 3) have released the stalled ripening of critical September berries from the cold/wet grip of late August.
The trouble started back in spring when record low temperatures killed scattered blooming in blueberry flowers in the valley (for July ripening) and extended the mid-mountain snowpack, delaying flowering and fruit set of the higher (> 1000-m) elevation fall berries.
Bears forage the valley berry crop from late June through October and the high elevation crop from August through October. The most important (highest abundance and sugar content) berries are blueberries and huckleberries (Vaccinium spp.), followed by the abundantly clustered Sitka-mountain ash berries. Berries are the only natural food in Whistler that allows bears to gain weight for successful winter denning from November to April and cub production in January.
Bears are the main force behind the rate of berry patch growth. As heavy concentrations of scat (bear droppings) are deposited throughout berry patches (as bears walk from patch to patch), seeds are dispersed and gaps between shrubs are slowly filled. Young berry shrubs half the size/area of established mature plants (established in new openings) can produce up to 400 berries because of maximum exposure to sunlight and little competition with overstory/regenerating conifers.
Why bears suffer then from shortages in berries, is not (currently) due to habitat loss, rather, to extreme scales in local weather. Too much rain delays and/or rots berries and too much sun limits berry size, leading to shriveled berries. A cold/wet spring can also prevent bees from navigating to flowers, reducing pollination and subsequent berry availability. As soon as a berry shrub becomes stressed (from extreme weather), the berries are the first to suffer as the plant directs all energy in coping.
The late success in this year’s berry crop could yield 15-30 cubs in 2009, because of 17 adult females resident to the ski area, 15 are considered pregnant (all observed in breeding in June-July 2008). Only two bears produced a total of three cubs this year (five of seven pregnant females failed to produce cubs last winter and the other 10 females were separating from 18 yearlings).
Breeding in spring does not guarantee cubs in January. Pregnant females can delay fertilized eggs from early August through November. Implantation and fetal development only occurs if females gain enough weight from the berry season. If they fall short, the eggs are reabsorbed and that female bumps to the next year’s cycle, which happened to five of seven ski area female’s in 2008.
If these 15 females are successful in cub production, that would leave at least two adult females for breeding next spring, resulting in heightened aggression by males attempting to kill spring cubs and forcing mothers back into potential breeding within the same season.
Since 1994, there has always been relative balance between female cycles (mothers with cubs vs. mothers with separating yearlings). This spring has seen the highest number of breeding females in the ski area, which represent about 75 per cent of adult females in Whistler Resort.
Another compounding variable is that two mothers in 2007 and one mother in 2008 have chosen to rear yearlings an additional year. The future of climate change and its influence on the bears' critical fall berry crop may be causing females to develop strategies that allow for longer investment of cubs, resulting in less cub production in a life time.
As of late August, the berry crop in the ski area was 25 per cent ripe, 25 per cent failed, and 50 per cent unripened. After nine days of sunshine and temperatures reaching 24 degrees Celcius (with milder overnight temperatures), berry ripening has reached nearly 75 per cent between 1,000-1,600-metres elevation, which is considered high and is supporting higher numbers of bears each day.
The forecast is ideal for continued ripening and berry support through late September.
Remember keep garbage and recycling away from bears and do not use containers that are ¾ full.