Effects of emergency winter supplemental feeding on survival of mule deer

Abstract Ungulates in temperate regions can experience high mortality during severe winters, which poses significant ecological and economic challenges for wildlife managers. To mitigate these effects, emergency winter‐feeding programs are often implemented, although their effectiveness remains uncertain. In response to high snowfall and prolonged winter conditions in 2023, the Utah Division of Wildlife Resources implemented an emergency feeding program aimed at reducing mortality among mule deer ( Odocoileus hemionus ). We evaluated the impact of this effort by monitoring survival of 102 mule deer with global positioning system (GPS) collars across fed (27 adults, 21 fawns) and non‐fed groups (45 adults, 9 fawns). Additionally, we assessed the body condition of adult females using estimates of ingesta‐free body fat percentage via ultrasonography. The program distributed 305 metric tons of feed at a cost of $213,500, with additional logistical expenses totaling $122,246. Of the latter amount, volunteers contributed $94,534. Adult females without supplemental feeding had a faster rate of fat loss (β = −0.01, 95% CI = −0.009–−0.001) and low overwinter survival (58%; SE = 0.07) compared to the fed group (81%; SE = 0.07). Fawn survival in the fed group was 53% (SE = 0.11), while no fawns survived in the non‐fed group. Malnutrition was the primary cause of mortality in both groups. Key factors contributing to increased survival in the fed deer included the timely and sustained feeding, ration composition, strategic site selection, and distribution methods at feeding sites. Logistical support from volunteers was crucial for the timely implementation of the program. The program incurred a total expenditure of $335,746, resulting in the survival of an estimated 1,099 mule deer at an average cost of $305.50 per deer. Although the program successfully enhanced overwinter survival, particularly among the most vulnerable group—fawns—the substantial costs involved underscore the necessity to carefully balance such interventions against their economic viability.