How climate change affects deer—experts draw findings from 20 years of research

Temperature, rainfall, snow and extreme weather events are all factors linked to climate change that directly affect wildlife. Understanding the impact of these factors on the physiology, population dynamics and distribution of different deer species is important for monitoring and protecting them.

The scientists involved in this study reviewed 20 years of research on 10 main deer species in boreal and temperate regions: moose, roe deer, wapiti, red deer, sika deer, fallow deer, white-tailed deer, mule deer, caribou and reindeer. Their analysis of 218 articles summarizes general trends of the effects of climate change on the physiology, behavior and population dynamics of these animals.

The paper is published in the journal Global Change Biology.

With the overall rise in temperatures, milder winters appear to be advantageous for many deer populations: they use less energy keeping warm and can find food more easily. However, for species living in colder climates such as reindeer or caribou, winter temperature variations can cause snow to melt and refreeze, covering vegetation under an ice sheet that makes the lichens the animals usually feed on inaccessible.

Similarly, hotter and drier summers could exceed deer populations’ physiological tolerances, mainly due to heat stress and parasites. In the short term, the animals’ physical condition could deteriorate; in the long term, some species could move further north, which would change their distribution. This is already happening to moose, the largest deer species and one which is best adapted to cold climates.

Moose are quite heat sensitive, and the populations located further south, such as in southern Scandinavia, are more affected by climate change and could disappear from these areas. Some deer species can overcome these issues by seeking refuge in cooler habitats and reducing their daily activities during the hottest hours. However, these responses can negatively affect population dynamics over the long term.

When moose and roe deer are subjected to stress, their body mass declines. As the animals get smaller, there can be repercussions on subsequent generations, including reduced population growth.

Finally, warmer spring and autumn temperatures reduce snow cover and depth, which changes the migration timing and routes of caribou and red deer. The animals begin migrating earlier in spring and later in autumn; over time, these species could stop migrating all together.

This review provides a synthesis of how deer react to climate conditions, both now and in the future. The scientists also identified several areas for further research, including the potential impact of extreme weather events, snow type and wetter autumns on deer. These findings should also help wildlife, forest and park managers better understand how deer populations might react to future climate conditions and adapt their population management strategies to protect these animals.