With strong advances in DNA technology, researchers in Banff National Park are trying to get a better handle on the number of bears living in the Bow Valley and surrounding wilderness.
Researchers have been able to use hair to identify and monitor individual grizzlies and black bears by using a method that didn’t require the stressful capture, drugging or handling of bears.
The non-invasive genetic sampling research project has detected a total of 80 individual grizzly bears and 85 individual black bears in the study area over a three-year period.
But, researchers are quick to say these are raw numbers only and a truer reflection of the resident population will be available in about six months time after the results are peer-reviewed and heavily scrutinized.
“I want to stress this is not a population estimate,” said wildlife biologist Mike Sawaya, a PhD candidate in the ecology department at Western Transportation Institute at Montana State University. “This is simply what we identified.”
Sawaya presented some of the results of the 2006-2008 DNA study at a recent Parks Canada research update in Banff. He plans to defend his PhD research in September.
The DNA study area boundary encompasses an area that extends at least 14 kilometres in all directions from a stretch of the Trans-Canada Highway between the park’s east gate to Castle Junction.
Part of the study focused on 20 wildlife crossing structures – both underpasses and overpasses – along that 43-km section of the highway.
Since the mid-1990s, as part of a separate long-term study, there have been a total of 198,811 crossings by wildlife, including 182,106 ungulate crossings, 5,547 wolf crossings and 1,493 cougar crossings.
There were 1,317 black bear crossings and 873 grizzly bear crossings, but one of the problems is researchers had no idea how many individual bears those numbers actually represented – and they wanted to get those answers.
“How many individuals are using the crossings?” said Sawaya. “Is it 873 bears crossing one time or one bear crossing 873 times?”
The results now show that 11 individual grizzlies (six males, five females) used the structures in 2006, 12 (six of each sex) used them in 2007 and 10 (five males, five females) in 2008.
There were 11 black bears in 2006, eight in 2007 and nine in 2008.
The total number of individuals detected using the crossing structures over the three-year period was 17 black bears and 15 grizzly bears.
The DNA study concludes a significant portion of the bear population is using the wildlife crossing structures to safely get across the busy highway.
That said, just a few individuals are responsible for the bulk of the use.
“Some of the bears using the crossings less frequently are probably juveniles or sub-adults, some of which may be offspring of the adults,” said Sawaya.
“A few individual grizzly bears appear to be using the crossings more and more each year, probably as a result of them becoming more and more comfortable using the structures in their home range movements.”
The study shows a major amount of the black bear crossings took place east of Banff, whereas the bulk of grizzly bear crossings were west of the townsite.
Sawaya said the majority of grizzly bear crossings were at three crossing structures in particular – both of the overpasses and the Healy open span underpass.
“Females were detected at six of the crossing structures, but males at a lot more. This suggests to me that males are a bit more flexible in what they’re willing to use,” said Sawaya.
“What was revealing is 10 of the 15 individual grizzlies over the three-year total were detected at the overpasses. If you were to mitigate for grizzly bears, I would suggest an open span underpass or overpasses.”
Sawaya said the number of bear crossings peaked early in the summer.
“Bears are concentrated down lower in the valley and there’s a lot of snow up higher. It’s also the breeding season, so bears are moving around a lot more to try to find mates,” he said.
The study also sought to determine the number of individual male and female black and grizzly bears in the population surrounding the Trans-Canada Highway.
Chains of barbed wire were strung around trees and bears were lured in with a liquid bait scent. These hair traps, 420 in total, were fairly evening distributed north and south of the highway.
Researchers also attached barbed wire to about 300 trees where bears are known to rub themselves, and where they leave behind hair for DNA analysis.
Through DNA collection at the hair traps, 30 individual grizzly bears were detected in 2006 (males 16, females 14) and 29 in 2008 (12 males and 17 females). There were 40 black bears in 2006 and 57 in 2008.
Rub trees detected 40 grizzly bears in 2006 (25 males and 15 females), 46 in 2007 (30 males and 16 females) and 43 in 2008 (24 males and 19 females),
There were two black bears in 2006, 11 in 2007 and six in 2008.
Sawaya said 89.4 per cent of black bears were identified with DNA samples taken from hair traps alone, while 91.2 per cent of grizzly bears were with rub trees alone.
For black bears, Sawaya said hair traps seem to have higher detection rates than rub trees in Banff National Park, whereas rub trees have a higher detection rates for grizzly bears.
“Rub trees are a powerful method to use to look at long-term trends and abundance of grizzly bears,” he said.
Sawaya said DNA data can be used to produce population estimates, but actual estimates are based on statistical models of the data as opposed to the raw numbers he presented.
He said good population estimates use statistics to account for both the number of bears missed with the sampling methods and the number of bears that spend little time in the study area.
“The numbers I presented were total counts of individuals identified on my study area through all three sampling methods combined for all three years,” he said.
“Population estimates are always given on a yearly basis, so the fact 80 grizzlies were detected in my study area over three years is somewhat meaningless since bear density and distribution can change dramatically from year to year.”
Sawaya said bears moved into and out of the study area, particularly during their seasonal movement patterns since the study area is so small.
“This means that bears detected on a rub tree or hair trap may simply be passing through or staying for a very short period of time, more transient than resident,” he said.
“Also, bears detected on the edge of the grid may spend almost no time in the study area, so total counts can actually be quite a bit higher than estimates when a study area is small.”
Sawaya said DNA counts also include an unknown number of cubs and most estimates of bear populations traditionally only include independent adult or sub-adult bears.
“Cubs can represent 20-30 per cent of a population and total counts include cubs; the number of cubs must be factored into population estimates or presented as estimates of the total population,” he said.
