Heat Is Stealing Sleep from Wildlife — New Studies Warn of Long‑Term Harm

Rising temperatures disrupt sleep in wild mammals, researchers warn

Insomnia isn't just a human problem. Two new field studies show that extreme heat and humidity can substantially degrade sleep in wild European mammals — a worrying signal as the planet warms.

What the studies found

The first study, published in Proceedings of the Royal Society B, tracked wild boar in the Czech Republic and found they slept about 17% less on hot summer days than on colder (and sometimes rainier) winter days. Researchers reported that summer sleep was "shorter, more fragmented, and of lower quality at higher temperature."

The second paper, in Animal Behaviour, found that Irish deer fawns also showed poorer sleep when exposed to high temperatures and/or high humidity. Although studies of sleep in wild animals remain relatively scarce, similar heat-related sleep effects have been observed in other species such as fruit bats.

Why this matters

Sleep supports immune function, memory consolidation, energy balance and recovery from stress. As Isabella Capellini, a co-author of the boar study, warned:

"Given the major role sleep plays in overall health, our results signal that global warming, and the associated increase in extreme climatic events, are likely to negatively impact sleep, and consequently health, in wildlife."

Briana Abrahms (quoted in Vox) added that reduced sleep represents "a new axis of stress" from climate change: animals — like humans — need sleep to recover from other stressors, so heat-driven sleep loss may compound other negative effects.

Potential ecological consequences

• Weakened immune systems could increase disease vulnerability.
• Shifts in activity, habitat selection or migration to avoid heat could disturb local ecosystems and food webs.
• Chronic sleep disruption may reduce reproductive success, foraging efficiency and survival over time.

Euan Mortlock, who led both studies, emphasized the scarcity of data on sleep in the wild and the need for more field research: "There is an enormous gap in our understanding of sleep in the wild. But with new methods, we can start to peek behind the curtain."

Small actions can help

While no single study solves the climate crisis, researchers note that collective, climate-friendly choices slow warming and help protect wildlife. Simple actions — composting kitchen scraps, walking or biking instead of driving, reducing energy waste — add up to reduce heat stress on animals and ecosystems.

Bottom line: Emerging field evidence suggests rising temperatures are already degrading wildlife sleep. That disruption could have cascading effects on health and ecosystems, so researchers call for more field studies and for actions that slow warming.