Statewide, 67% of fawns and 93% of calves with tracking collars have survived through mid-March.

Statewide winter survival for mule deer fawns and elk calves has shown to be right in line with years past. Through the middle of March 2025, 67% of fawns and 93% of calves (with tracking collars) have neared the finish line on their first winter.

But, the race isn’t over just yet.

Depending on weather, late-March and April are often when fawn and calf mortality is the highest because the young animals' fat reserves are largely depleted, and their digestive systems need time to convert to digesting fresh, green forage.

“Right now, in the middle of April, things are looking promising for both deer and elk,” said Toby Boudreau, Fish and Game’s Deer and Elk Coordinator. “We’ll know for sure what survival will look like in the coming month, after we’ve tallied up the final numbers.”

For mule deer fawns in particular, a stretch of cold, wet weather in the early spring can substantially decrease survival, and biologists can see winter-related mortality as late as May.

A glimpse into winter survival

Winter survival is typically the biggest single factor affecting mule deer herds, and the long-term average is about 60% of fawns surviving their first winter, but during hard winters that can be significantly lower. Earlier this winter, Fish and Game biologists captured and collared 173 mule deer fawns and 178 elk calves in various parts of the state to monitor herd health and track their survival throughout winter.

As mentioned above, by the middle of March, 67% of collared fawns and 93% of collared calves were still alive, and here's how that compares with recent years:

• 82% fawns and 93% calves in 2023-24
• 46% fawns and 86% calves in 2022-23
• 63% fawns and 85% calves in 2021-22
• 71% fawns and 85% calves in 2020-21
• 73% fawns and 84% calves in 2019-20
• 58% fawns and 84% calves in 2018-19
• 69% fawns and 72% calves in 2017-18

“Fawn weights, which indicate how likely they are to survive winter, were high in many places in southern Idaho when we captured and collared fawns in December and January, and we have so far observed above-average survival,” said Toby Boudreau. “Heavier fawns and mild winters are good for mule deer populations.”

Boudreau added that survival of fawns throughout the state is not uniform, and that it ranges from 100% to 62% survival, depending on the unit where the fawns were collared.

Why it all matters

Fawn and calf survival is critical to growing herds or sustaining current populations. Survival of young mule deer has a direct relation to the fall deer harvest because yearling bucks typically make up a significant portion of the overall mule deer harvest.

In addition to all that, knowing how many collared animals die each winter gives Fish and Game wildlife biologists a good estimate of how the rest of the population is faring. And knowing just how many animals—in this case, deer and elk—are out on the landscape is crucial when it comes to setting seasons and providing hunting opportunities.