Roadways in bear habitat are having a discernable affect on the population of grizzly bears in the province of Alberta.
Most affected, however, are female grizzly bears with cubs, which research has shown are more likely to be around roads and have higher rates of human-caused mortality as a result.
Grizzly bear researcher Gordon Stenhouse, with the Foothills Research Institute, presented his most recent data on the issue of road densities and their affect on the species at a Wildsmart speaker’s series in Canmore last week.
He said with female bears and cubs spending more time around open roads that traverse grizzly bear habitat, it is time to change our approach to accessing those areas as a result.
“When a road is built for whatever reason, to think that we should use it at all times for all purposes … we might want to think about that if we want to maintain bears,” Stenhouse said. “We might also have to undertake access closures and access restoration. We may have to say we are going to have to manage landscapes differently than we have in the past.”
He said by having a direct linkage between road densities and population trajectory for the species, land managers have a better understanding of what the consequences of open roads means to grizzly bear populations.
Stenhouse said people influence bear mortality in various ways, pointing to the 31 known grizzly bears killed in 2013, of which 26 were directly related to people.
“We need to reduce human-caused mortality, that hasn’t changed. In fact, if you look at this year’s numbers clearly it hasn’t changed and you might take a five-year or six-year average and try to smooth out the data, but the question is where are those mortalities occurring? If those mortalities are occurring to adult females with cubs adjacent to roadways in a population unit where you have 42 animals, you have a big problem.”
As for why females and cubs frequent roads, Stenhouse said it is because the routes provide a food source for them. Most roadways have had vegetation put down to stabilize the soil and he said plants like dandelions and clover are “like candy for bears, they come and they feed on that.”
Another reason is because ungulates also feed on the vegetation, providing another source of food for bears, especially when they are hit by vehicles on the roads and left behind as road kill.
The fact that females with cubs are more likely to die, said Stenhouse, is a significant loss for the species overall.
“You are losing reproductive females and their cubs,” he said. “You are not just losing one bear, you are losing a family unit and female bears take five to seven years to become sexually mature – these are big impact animals to lose.”
In 2004, Stenhouse began a population inventory of grizzly bears in the province using DNA. While the project took several years and several million dollars to complete, this year he will repeat the first DNA population inventory done 10 years ago in the Yellowhead area.
“By repeating it, we will know what happened in the population over a 10-year period,” he said. “That won’t give us very good trend information, but it will tell us what the minimum count of the population is and it will give us information on spatial distribution.
“But most importantly, from my standpoint, is we have 10 years of landscape change. We have 10 years to see where forestry cut blocks have gone in, where roads have gone in, where roads with gates have gone in and we can look at what the bear response has been.”
Stenhouse has been researching grizzly bears, their habitat and mortality risks since 1999 when he began using radio collars to track animals. Along with DNA surveys, the work showed there is believed to be less than 700 bears in the province and of those, 359 are mature adults. As a result, grizzly bears were listed as threatened in 2010.
That then led the way for the first grizzly bear recovery plan and Stenhouse was tasked with identifying conservation areas for bears based on habitat values. The early data showed the survival of grizzlies declines as road densities increase.
A road density of 0.6 kilometres per square kilometer for core habitat and 1.2 km for secondary habitat was identified as a result of the science at the time.
“The notion was that by coming up with road density thresholds in core habitat and in secondary habitat we wanted to reduce human-caused mortality,” he said.
With more data and research complete, Stenhouse said he has learned that road densities affect available denning habitat for bears.
“One thing we have learned is that as road density goes up, the probability of den site occurrence declines, so the more roads we put in we are actually losing den habitat,” he said.
Another new finding out of Stenhouse’s research is connecting population trends with road densities. Using age specific and reproductive specific survival data into a population model, he said at a road density of 0.85 km per square km of land, the population is in decline. The model applied to watershed units in grizzly bear habitat has identified where populations are in decline.
“Right now we know from our work where we have watershed units in a state of decline and if you continue to put more roads in without restriction on access or motorized use, you are moving up to that number,” he said.
“At 0.85 that is when you have decline. When you are trying to recover populations you should definitely stay below 0.6 – that hasn’t changed. It doesn’t mean we have to shoot for another number, what it tells you when you get to that number you have population decline.”
