Banff's grizzly bear population may be declining
The reason grizzly bears rub up and down against trees still divides and mystifies many researchers – but a new study in Banff National Park is said to be the first ever to directly use rub trees to estimate a bear population.
The good news is the study indicates rub trees are an effective and low-cost way to monitor grizzlies in the central Canadian Rockies – the bad news is that the same study suggests Banff’s grizzly bear population may be in decline.
The study, led by wildlife biologist Mike Sawaya, put grizzly bear abundance in the Bow Valley and surrounding areas at 73 in 2006 and 50 in 2008.
But because the study area was so small and the time frame so limited, officials say it’s hard to distinguish between emigration, mortality and low recruitment of grizzly bears as the cause of the decline.
“We provided empirical evidence that the grizzly bear population may have declined in the Bow Valley between 2006 and 2008,” said Sawaya, who worked in the ecology department at Montana State University at the time of the study.
“It’s definitely concerning, but has it continued to decline? Is this a long-term trend? I don’t know and that’s why I’m reluctant to promote it as a main part of the paper.”
Sawaya recently had the research published in the on-line journal, PLoS ONE.
His work evaluated the potential of hair traps and bear rub tree surveys to estimate population abundance and trends of both grizzly bears and black bear populations in Banff National Park.
During the two years that hair trap and bear rub sampling was conducted simultaneously, most of the individual grizzly bears were identified with rub trees and the majority of black bear individuals were detected with hair traps.
Sawaya said the study revealed hair traps had high detection rates for female grizzlies as well as male and female black bears, but extremely low detection rates for male grizzlies.
On the other hand, he said, rub trees were highly successful in detecting both male and female grizzly bears, but not nearly as successful at picking up black bears.
“Our results suggest that bear rub surveys would provide an efficient and powerful means to inventory and monitor grizzly bear populations in the central Canadian Rockies,” Sawaya said.
Bill Hunt, resource conservation manager for Banff National Park, said the decline in grizzly bear numbers is “cause for concern”, though he said the study area was small and not representative of the national park as a whole.
And, he said, the research may not necessarily mean bears have died; rather it could be related to grizzly bears moving in and out of the area over the time period.
“The reason they may or may not be there could be some have died, but it could also be that some left or came into the area – immigration and emigration,” said Hunt.
“We’re hopeful that immigration and emigration is part of what we’re seeing because it would be very shocking if we lost that many bears in that time period.”
Between 1994 and 2002, a study of radio-collared grizzly bears in Banff National Park determined the population was slightly increasing, while also being one of the slowest reproducing populations ever studied.
But that same high-profile study also concluded Banff’s grizzly population would have declined if adult female mortality increased during the study timeframe.
Then, between 2002 and 2008, adult female grizzly mortality rates exceeded Banff’s established threshold. In fact, human-caused independent female mortality more than doubled after the earlier study.
Sawaya said the bear estimates from his study could be driven by annual fluctuations in food availability, such as buffalo berries, or patterns of reproduction, or it could reflect the dynamics of a population returning to a more stable size for the Bow Valley after a spike in reproduction.
He said adult female bears, along with the accompanied reductions in births, could explain the decline detected in the study area, even if emigration, mortality and immigration were constant.
“Whatever the drivers may be, our estimates show concordance with previous research suggesting that the Bow Valley may act as an attractive sink for grizzly bears in the central Canadian Rockies Mountains,” Sawaya said. “But these findings should be confirmed with long-term monitoring across a much larger geographic area.”
Mike Gibeau, a renowned grizzly bear expert and retired Parks Canada carnivore specialist, said the results of this non-invasive study mirror other studies that have been indicating a decline.
“This is a major red flag. If we can pick up change in that short of a time frame, the red flag should go up,” said Gibeau, also a co-author on Sawaya’s paper.
“We’ve been aware of a declining population from annual monitoring reports published for a number of years now. There’s been increasing mortality, especially in the female component of the population.”
But Gibeau said the answer lies not in more study of grizzly bears, but on fixing the problem that is leading to grizzly bear mortality, noting the train tracks are the single biggest killer of grizzlies in Banff.
Eleven grizzly bears have died on the train tracks in Banff since 2000, including nine since 2005.
“The fundamental problem is they are selectively determining what the problem is – all the current efforts are focused on doing something with the bears, yet the problem is with those spilling grain,” Gibeau said.
“They need to fix the reason bears are dying – that’s ultimately what they need to do. With each additional female we lose, we’re digging ourselves a deeper hole.”
Gibeau said there is action that can be taken, such as fencing off problem areas, modifying steep banks to allow bears to escape and slowing down trains through the parks.
“There’s a whole bunch of options that they could have spent money on to actually improve the situation on the ground, but they chose an option to study the problem more, by and large,” he said.
“By studying it more, they don’t solve the problem, they kick the ultimate problem further down the road and hope that in studying it more something miraculous will happen.”
Meanwhile, Hunt said the good news is Sawaya’s study gives Parks Canada confidence to look at using non-invasive rub trees over a larger area for a longer period of time to “get a better understanding of what’s going on.’
“We’ve got our collaring program going on right now and we’re looking at what we can get in place for rub trees as well,” Hunt said. “But we’re still waiting to find out what our budgets are.”
The 2,246-kilometre Bow Valley Study area was mostly contained in Banff National Park, but it did extend slightly into Kootenay National Park and Alberta provincial lands.
The initial study area included a 14-km buffer around a 45-km stretch of the mitigated Trans-Canada Highway in order to assess the wildlife crossing structures for grizzly and black bears in the Bow Valley.
Hair traps consisted of a 25m length of barbed wire nailed to a series of trees to form an enclosure. Bears were lured into the enclosure with a liquid scent of cattle blood and decomposed fish oil on rotten wood.
As part of the study, 321 bear rub trees were identified based on characteristics such as smoothed bark, claw marks and bear paths. They nailed short pieces of barbed wire to the tree to collect bear hair in 2006-08.
Sawaya said population monitoring is particularly important in national parks, such as Banff National Park, because protected areas often serve as source populations for much larger geographic areas.
He pointed to the fact that in 2010, the Alberta government listed the grizzly bear as threatened based on over a decade on radio-telemetry research and five years of DNA-based population surveys.
“This designation increased the prominence of Banff National Park for grizzly bears in Alberta and added an urgency to wildlife managers’ need for cost-effective techniques to inventory and monitor bear populations,” he said.
“There’s a population listed in Alberta as threatened and, given our results, it’s time to start acting and it’s time to start getting a better handle on why this is going on and how widespread this might be.”
The rubbing of trees by grizzlies has been documented throughout the northern hemisphere, but researchers have many theories on why the bears rub, bite and claw at trees.
Some speculate bears are scratching an itch, while other studies suggest the bruins rub trees as a form of chemical communication. Yet another theory is bears are covering themselves in sap as an insect repellent.
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