Agency is developing more-accurate methodology
WDFW biologists were in the air in the Methow Valley for a total of five days this month. The first two days were devoted to the annual deer survey, and the following three days were focused on launching a new research project that seeks to make deer counts more accurate.
“Overall, population is probably down a bit,” Fitkin said this week. He emphasized that data from the survey is still preliminary and will be analyzed in more detail. “When we get all the numbers crunched, ratios will likely change a little bit … after correction factors are applied.”
The preliminary survey findings put the buck/doe ratio at 16 bucks/100 does, which compares to a 10-year average of 23 bucks per 100 does. This year’s numbers are “still above the 15/100 minimum [buck-to-doe ratio] in our management plan,” Fitkin said.
The buck numbers are a reflection of “harvest pressure,” which is tied to the “number of hunters and number of days they hunt,” Fitkin said. “Our harvest pressure stays pretty consistent, but if there are less bucks on the landscape overall, hunters probably are going to take a higher percentage.”
The state expanded the hunting season from nine days to 11 days four years ago, and since then “the buck/doe ratio inched down.” If it were to drop below the 15 bucks/100 does ratio that is set out in the state mule deer management plan, Fitkin said, “we’d start thinking about how to adjust the [hunting] season.”
Looking for trends
One year’s statistics aren’t usually enough to prompt a change in the hunting season, Fitkin said. The wildlife department generally establishes seasons on three-year cycles. “We want to see trends” before instituting changes, he said.
The fawn/doe ratio this year is 65/100, “almost identical to last year,” which found 64 fawns per 100 does, Fitkin said. The 10-year average of fawns to does is 76/100. The lower fawn numbers are probably a result of habitat impacts that affect birth rates, he said.
The Carlton Complex Fire of 2014 damaged large tracts of mule deer winter range, burning bitterbrush and other shrubs that provide winter forage for deer in the Methow Valley. Although the range is slowly recovering, the fire’s lingering effects may contribute to a lower fawn/doe ratio, Fitkin said.
“My suspicion is productivity is down. The combined effects of summer drought and fires on the winter range is at least partially responsible for the dip in fawn/doe ratios,” Fitkin said. “When deer are nutritionally stressed, they don’t have as many fawns. It makes it harder for does. They may not have as many twins, or may even reabsorb the fetus.”
While flying over winter range that burned in 2014, Fitkin said he saw some positive signs that the landscape is making a comeback. “I would say shrub recovery is beginning to get noticeable,” he said. “There is a lot of ceanothus coming in, and deer really like that, it can be good winter forage. It’s a fire-adapted plant. Fire tends to release ceanothus. On the flip side of that is bitterbrush. It’s slow to recover.”
As part of the survey, WDFW counts and classifies deer by age and sex, and extrapolates on those numbers to estimate the total population. During the two-day survey, Fitkin counted 1,150 deer, which he estimated “is less than 10 percent of the migratory herd in the Methow Valley.”
One deer, two deer…
Western Okanogan County, including the Methow Valley, is home to the largest migratory mule deer population in Washington, Fitkin said. The Methow Valley has the “largest wintering concentrations” of mule deer in the state according to a 2016 WDFW mule deer management plan.
WDFW estimates that 47,000 mule deer live in the East Slopes of the Cascades management area, bounded to the north by the border with British Columbia, the crest of the Cascade Mountains to the west, the Columbia and Okanogan Rivers to the east, and I-90 to the south.
The state management plan notes that mule deer, “an icon of the American West,” are important to people of Washington for viewing and hunting opportunities and for the economic benefits those activities bring to local communities. Additionally, the deer have long been a source of food and clothing for native people.
Good management of the state’s mule deer herd requires having an accurate count, but that has always been problematic, Fitkin said. “States have wrestled with this all over the West. It’s very difficult to go out and census deer, i.e., count them all,” he said.
WDFW conducts aerial deer surveys throughout the state. It’s expensive and time-consuming to fly over winter range and count individual animals and, even if money and time weren’t an issue, it’s simply not possible to see every deer because they may be hidden by vegetation or landscape features, Fitkin said.
That’s where a new research project, that began with this month’s aerial surveys in the Methow Valley, comes in. The project is identifying factors that prevent an accurate count, such as vegetation and landscape that prevent deer from being seen and counted. The project will develop computer models that will correct for those factors, said Sara Hansen, WDFW statewide deer specialist.
To conduct the research, biologists are locating mule deer does in the Methow Valley that have been captured and fitted with GPS radio collars as part of a separate study of predator and prey interactions being conducted by the University of Washington. About 80 does currently have collars.
“We’re trying to figure out for those we see, what are the factors involved. For the collared deer we missed, we can home in on the GPS collar and … assess why we missed her,” Hansen said. “We take the times we saw deer and build a model for the times we missed deer. The model takes into account landscape variables that result in missing deer and corrects for animals we’ve missed.”
The approach is based on a “sightability model,” a method for correcting aerial surveys for undetected animals that has become widely used to estimate wildlife populations.
To gather data for the research, Fitkin flew with two other WDFW biologists. Fitkin counted deer and described conditions on the ground such as snow cover, tree cover and foliage. Another person recorded and provided secondary observation, and the third person monitored radio telemetry to locate collared deer.
The state of Idaho developed a similar method for counting deer, but differences in terrain and vegetation means Idaho’s model isn’t well-suited to Washington, Fitkin said.
Two more aerial surveys that will track the collared deer in the Methow Valley are planned this winter to gather data for the project, Hansen said. The data collection will likely continue for the next two or three years before a model is developed and used by WDFW to estimate the mule deer population, she said.
“It takes time to accrue enough data to deploy the model. This isn’t rocket science. It’s harder,” Hansen said.
“Hopefully,” she said, “we’ll have a better way to estimate the population, and better deer management. It’s a good way to gauge how deer are doing on the landscape … so we’re setting [hunting] seasons as accurately as we can.”