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Bear Update: Spring abundance and reproductive synchrony



During the first two months (April, May) of the pre-berry season, I identified a minimum 72 individual black bears including cubs (35M, 37F) in the Whistler-Blackcomb ski area and adjacent Whistler valley (Function Junction to Lost Lake).

An additional 14 (10M, 4 F) different bears were identified along a recreational corridor from Highway 99 to the Callaghan Nordic site and 11 (8M, 3F) different bears from Brandywine to Alice Lake Provincial Park along Highway 99.

Two significant events in bear population ecology unfolded this spring: record low temperatures and potential reproductive synchrony.

The extension of winter into early spring by record low temperatures reduced spring forage for bears and crowded them into the narrow elevation band of 675 to 800 metres for nearly two months. Slightly warmer temperatures through late May and into early June are allowing bears to disperse from high concentrations near valley bottom to available green-up at 1,200 metres elevation (mid-mountain). Large snow cover (but with normal winter snow pack) remains above mid-mountain. The question now is: how much longer will colder temperatures persist to delay berry phenology (ripening) in July (valley) and August (mid-above mountain)?

The second event to impact population ecology this year began last fall when a cooler, wetter summer reduced berry feeding for bears. Of 15 adult females in the ski area, nine emerged this spring with yearlings (two have two-year olds) and six were due to produce cubs this past winter.

Only one of six females produced cubs.

I’m assuming that the remaining five females failed to implant fertilized eggs in early December 2007 as they emerged from their dens with no litters or evidence there of this spring.

The power of longevity in field studies (1994-2008) is supporting the correlation between the biology of known female bears and the impacts of localized climate change on berry supply. The availability of berries regulates weight gain in bears.

Breeding begins before the berry season in late May and ends in late July. Female bears have the ability to delay fertilized eggs from implanting during mid-August to late November so that the female’s body has time to ensure healthy weight gain from berries. If weight gain is high, two-to-three eggs are implanted in early December. If weight gain is border line, one egg will implant. If weight gain is poor, resulting only in supporting the female through six months of winter denning, then eggs are dissolved and reabsorbed, bumping the female’s cycle form one year to the next.

The result of this climate-induced shifting in cycles is reproductive synchrony — when all female cycles fall on the same year. I have never observed synchronized reproduction in Whistler bears during the last 15 years. With 14 of 15 females potentially breeding this spring in the ski area population, it could yield high cub production in 2009 if we have a good berry crop this year.

However, some mothers may not separate from yearlings this spring due to the small size of yearlings (from poor weight gain last fall) and the likelihood of another poor berry crop because of colder temperatures this year. Also, the status of maturing daughters and their contribution to cub production needs to be investigated.

A question that erupts constantly with me is: Can mother bears sense a shortage in food supply as early as the breeding period (June-July)? And if so, can they make choices to keep the family unit together and avoid breeding (as Zoe and three yearlings did in 2007) and/or allow offspring to return (after the mother breeds) re-uniting the family group (as Katie and two yearlings did in 2007)?

If 14 females do breed this spring, followed by a good berry crop this fall, 2009 cub production would be high and the availability of single adult females would be low, resulting in increased aggression from dominant males.

Males may sometimes kill cubs during the breeding period to force mothers back into estrus before their next cycle (if not enough single females exist).

High cub production also yields a potential increase in sub-adult bears into the population two years later that are more likely to become lured to non-natural foods near people when avoiding larger bears and their mothers’ breeding range.

With the population of resident females nearing reproductive synchrony and the cooler temperatures delaying berry ripening, us humans are in for another “close relationship” with bears this year.

Next column I will describe the status of resident bears and predict berry ripening dates.

If anyone does observe a mother and cub please let me know at 604-698-6709 or e-mail Many thanks to all that support this important work.

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