Winter scores flag fawn risk for the next fall

STEP 1 · Cedar yards

Extra snow and late green-up fall outside the score

Our rule starts with the score for your permit area or your management unit on the scale that state actually uses. Next come two checks the formula leaves out. One check is snow stacked well past the depth that earns a point. The other is a green-up that shows up late. Either problem can push deer harder than a moderate rating implies.

STEP 2 · State cutoffs

Minnesota and Wisconsin do not share a severe line

The Minnesota Department of Natural Resources builds its winter severity index across a fixed window. Counting starts Nov. 1 and ends May 31. Any day whose temperature is 0 F or lower adds one point. Another point is added when snow depth reaches 15 inches or deeper. Daily totals can be 0, 1 or 2. Season sums of 50 or lower count as mild. Sums from 51 to 119 count as moderate. Sums of 120 or higher count as severe. Those labels were reset in 2020. Northern forest deer permit areas supply 36 years of these scores. Winters finishing at 50 or lower were 25% of them. Winters scoring from 51 to 119 were 50% of them. The remaining share was 25% and those winters reached 120 or higher.

The Wisconsin Department of Natural Resources starts the count later and requires deeper snow. Daily points begin Dec. 1 and finish April 30. A low at 0 F or colder adds one point. A snow depth of 18 inches or more adds one point. A day that hits both adds 2. Labels run mild under 50, moderate from 50 to 80, severe from 80 to 100 and very severe over 100. Wisconsin bases those names on observed associations of the index with winter death and with fawn production and with buck harvest the next year. Habitat and weather near home can differ from the regional score. Deer with better habitat tend to take less harm from extreme winter weather.

The Michigan DNR 2025 deer hunting preview does not give this day-by-day recipe. We read the 2025 text from the archive capture. The live page on the state site now carries the 2026 preview. Deep snow in 2024 to 2025 lasted nearly long enough to count as severe for the Upper Peninsula. Conditions were considerably worse for Upper Peninsula deer during six years among the prior 10. A methods PDF with Michigan's exact day-count formula would not open. Minnesota's 120 and Wisconsin's 100 are not Michigan severe thresholds in that preview.

Kautz and colleagues scored a research index from Nov. 1. One point came when the low dropped below minus 17.8 C. One point came when snow was deeper than 38.1 cm (15.0 inches). That temperature line and that 15.0-inch snow line match the Minnesota rules. The crew used the index on two study areas in the Upper Peninsula during 2009 to 2015. Do not swap this research index for the peninsula-wide figure Michigan managers put out.

STEP 3 · Doe collars

The second severe winter killed far fewer does

Minnesota's page says the index on its own is not predictive. Once snow is past 15 inches the energy drain on deer exceeds the drain from cold, and snow three feet deep still earns only the single point earned at 15 inches. Late green-up lands on pregnant does during late gestation and again while they nurse. The agency treats dense conifer as optimum winter cover where canopy closure is 70% or greater and food is close by. Yarding saves energy in open snow while piling more deer onto less browse.

The Minnesota DNR calls fawns typically the most vulnerable in a hard winter. Adult bucks come next and adult does come last. Fawns hold less fat and bucks spend the fall breeding. Does most often reach spring and then have to produce the fawns.

The same Minnesota page describes radio-collared deer followed for 15 years in northern forest habitat from 1991 to 2005. Densities were high in the severe winter of 1995 to 1996. Of 80 radio-collared adult does, 32% died. After fawns and adult bucks were folded in, estimated mortality for the whole forest zone was 40%. Very few newborn fawns lived through the following spring. The winter of 1996 to 1997 was severe too. That adult-doe cohort then died at 7.8%. Both production and survival of fawns were high. Minnesota's reading is that the opening winter took the weakest deer and reduced density. Many living does skipped nursing that summer and met the next winter in better condition. A second severe winter does not repeat those deaths by default.

Annual pregnancy rates average 90% among yearlings on that page. From age 2.5 through at least 15 years the rate for does is near 100%. Over half of those does carry twins. The agency says a rebound can happen if ordinary conditions last 3 to 4 years. Our paper on how harvests came back after herd shocks follows several states whose kill totals needed many seasons to rise. Those totals still are not a forecast.

STEP 4 · Melt timing

Snow-free days outweighed the score for collared does

Kautz and colleagues collared 147 pregnant does in two study areas on the Upper Peninsula. Every doe was older than 2.5 years. The years were 2009 to 2015. Their cumulative winter scores ran from 11 to 167. Survival during February through May spanned 0.22 to 0.89 by year. The mean of the yearly figures was 0.69. In the hazard model each extra point on the cumulative winter score lifted mortality risk by 1.9%. Each extra snow-free day cut risk by 8.2%. Body mass lowered risk 4.3% for every additional 2.2 pounds (1 kg). Weekly survival models gained nothing from age or from snow depth that week. Among mortalities whose cause was known, 78% were predation. Coyotes and wolves took the largest share of those deaths. Weekly mortality averaged 2.1% across February through May. From June through January the weekly average in these same deer was 0.6%. Late winter ran 3.5 times the earlier weekly rate.

Snow under 7 cm (2.8 inches) counts as snow-free in the paper. Days in that class are totaled from Feb. 1 until May 31. The authors tie faster condition loss to deep snow and cold, and they treat a late melt as the steeper late-winter risk. Snow that stays into April can kill deer even when the score is only moderate. Our read is that open ground returning while reserves remain lets deer get through a hard middle of winter.

Buck harvest in the Upper Peninsula rose once 2023 to 2024 proved extremely mild. Condition recovered from two harsher years before that winter. Southern Lower Peninsula deer are the other herd in the preview. The preview credits routinely mild winters there and abundant summer food for how rarely winter death hits them. Our Michigan two-herds paper sets the Upper Peninsula's winter cycle apart from farmland farther south. The preview warns that an average taken across the region might not show in results at a given hunting place.

STEP 5 · Evening watch

Repeat last year's fawn count on one route

Wisconsin connects the index to fawn production. The severity page we opened states no percent for the connection. The fawn-to-doe page describes late-summer observation ratios as usually lower in forest country than in farm country. It describes northern ratios as usually higher after mild winters. During August and September, staff and partners write down does and fawns and bucks. The agency says no unbiased method for a late-summer fawn-per-doe figure has been built. Counts from the roadside have tended to follow other clues about nutrition and about winter weather.

Use openings you pass anyway near the end of August and the start of September. Match last year's number of evenings. On those evenings tally adult does and fawns. Record every date and the length of each sit. A drop in your forest count after a severe winter fits the Wisconsin pattern when a farmland count nearby stays flat. Those evenings sample your route only and will not produce a recruitment rate.

Do not grade the winter from a statewide kill. Look at Minnesota's 2025 firearm registrations piled up on opening weekend. The shape of the pile follows season timing and hunter location. It leaves the prior June's fawn births unmeasured. Antlerless permits can move how many deer are killed while herd size stays the same. Our rule reads the winter score once spring posts it. Your own fawn count follows in late summer and harvest for your unit comes last.