Winter ‘severe’ for deer population: MNR


Data collected by the Ministry of Natural Resources on winter conditions so far show above-average weather severity for local deer—but not enough to cause dramatic changes in their population.
Current measurements at the MNR’s network of snow stations show that snow is deep in the Fort Frances District, ranging in depth from 65-71 cm in forest habitats, meaning deer movements are considered “very restricted.”
“Severe winters are common in Northwestern Ontario and in northern portions of deer range,” noted MNR area biologist Darryl McLeod.
“Deer, moose, and wolf populations will respond naturally,” he said.
McLeod also noted that while there’s some potential mortality on deer, there will be little overall impact to their numbers unless a consecutive severe winter follows next year.
Since 1952, networks of snow stations have been established in the Fort Frances District, which are used to evaluate winter weather severity for white-tailed deer.
These stations are located at Arbor Vitae (west of Fort Frances), Rice Bay (east of Fort Frances), and just south of Atikokan.
Snow depths, crust conditions, and wind chill all are collected on a weekly basis from these locations and then inputted into a provincial database.
Four indices of weather severity have been developed from this data—the Snow Depth Index (SDI), Ontario Weather Severity Index (OWSI), Passmore Snow Severity Index (PSSI), and Snow 50 (i.e., 50 days exceeding 50 cm)—to evaluate the impact winter weather may have on deer.
SDI is based on a measure of the cumulative weekly snow depth since the start of winter.
Deer movements are restricted when snow depths are greater than 50 cm, and considered “very restrictive” when depths exceed 63 cm.
Based on SDI and OWSI values recorded at Rice Bay during the last week of January, the probability of severe conditions at the end of winter is predicted to be greater than 80 percent by the MNR.
Severe winters can reduce deer populations through adult mortality, such as due to deep snow covering food, restricting access to browse, increased energy use due to cold temperatures and wind chill, and increased predation from wolves.
As well, a severe winter can reduce deer populations through pre- and post-natal fawn mortality—something the SDI and OWSI indices are used to predict.
Comparatively for the last week of January, Dryden District had a recorded snow depth of 65 cm, Kenora District 58 cm, and Sioux Lookout District 63 cm.
Fort Frances SDI ranged from 412-463 for that week, depending on the station, while the SDI for Dryden, Kenora, and Sioux Lookout was calculated at 508, 400, and 560, respectively.
So far this winter, the MNR hasn’t recorded severe weather when it comes to the moose population given moose movements generally are unrestricted with accumulations below 75 cm of uncrusted snow.