ESCANABA — Readers — and hunters — may be wondering what impact the mild winter may have on the white-tailed deer population. While mild and moderate winters make for low mortality and it is likely that a good number of fawns will be born this upcoming season, experts at the Michigan Department of Natural Resources, analyzing many years of data on the heavily-studied topic, say that multiple years in a row of a certain type of weather is needed to really have an effect on the deer population overall.

A mild winter means that deer did not struggle to stay nourished; therefore, pregnant does were probably able to obtain the necessary nutrition to give healthy births in a couple of months. The time of year when fawns are born is consistent — the whole population producing a crop of babies at the same time is an evolutionary trait called “predator swamping” and is meant to ensure that at least some live through the ever-present threat of predation. After difficult winters, fewer fawns may be born, or they may be too small and unhealthy to survive.

Mid-May and mid-June — deer birthing season — will probably be good for fawn production. However, for that generation to contribute to the general population and be considered “recruited” into the herd, they must be able to make it through the following winter. The overwhelming majority of deer harvested during hunting season are one-and-a-half, two-and-a-half, and three-and-a-half years old, hence the need for repeated seasons of survivable conditions before it can be said that there has been a population boom.

“In most years, it is the recruitment of fawns that drives deer population growth,” reads a report by DNR Wildlife Biologists Kristie Sitar and Brian Roell.

“To really see a big increase in your deer population, you need multiple mild winters in a row,” said DNR Wildlife Technician Colter Lubben. “Because all a mild winter does is — it gives you one year class.”

Come this hunting season, fawns from the spring of 2022 would be two-and-a-half years old, the median age harvested. But the past two winters were considered “severe” by the DNR’s metric — that is, there were more than 90 days that the average snow depth in the U.P. was greater than 12 inches. That’s two major barriers — first to production, then to recruitment — for that age class.

Records show that the winter of 2013 to 2014 was particularly nasty — about 120 days saw snow deeper than a foot. That year, said Lubben, the DNR was conducting a study of fawn survival rate in the Crystal Falls area, and 100% of the fawns tracked died before the winter was through.

“From whatever they collared in June, July, when they were born — by the next spring, not a single one of them made it,” Lubben said, adding that 60% of adult deer also died that winter.

There’s also something called “lag effect” that happens after extremely difficult winters. Some deer become so weakened that they continue to starve even after snowmelt. Lubben referred to these as “walking dead” — never able to replenish their health, they perish in the spring.

If an extreme winter happens again, the fat, healthy deer people are seeing now and the expected good fawn count might not make it to 2025. And the fawns that will be born this spring of course won’t be large enough for hunters to want to harvest before then.

However, most of the deer that were around and not harvested this past hunting season are likely still kicking. Part of the reason numbers drop in the winter is predation, which occurs more during winters that bring deep snow or extended snow coverage.

“The more severe winters are, the more susceptible (deer) are to predation because of deep snow,” Lubben explained. When snow is deep, deer cluster in areas that have reduced snow depths, like conifer groves, which provide good coverage. “And as deer are more concentrated, of course, it makes it easier for predators.

“The other thing that is important to note, in a severe winter, a deer’s nutrition is constantly declining,” Lubben continued. “Towards the end of winter, when they’re at their lowest, they are more susceptible to predation. They’re weak; they can’t run as well; they can’t get away.”

Those particular struggles weren’t present this year — only one day saw the average amount of snow in the U.P. at over 12 inches. The biggest threats to the current deer population are vehicle strikes; legal and illegal harvest; predation by coyotes, black bears, bobcats and wolves; natural mortality such as disease and drowning; and starvation, which becomes more likely if the winter of 2024 to 2025 brings back heavy snow.