Stress can do more than raise our blood pressure; it can also change our body temperature. The phenomenon has been known to physicians for centuries. It’s even seen by veterinarians. But despite years of study, why animals can heat up or cool down under stress has remained a mystery.  

In a new study, researchers from Trent University have uncovered the reason and it’s all about priorities. Sometimes it’s better to let body temperature drift and focus on avoiding the predator, or other more immediate threat, ahead. 

“We knew that responding to a stressful situation can cost a lot of energy. But we also knew that maintaining a constant body temperature — which is important for general health — can also be energetically costly,” says Joshua Tabh, a former Ph.D. student at Trent University and an author on the study. “So, when energy is in short supply, we suspected that animals should direct what energy they had toward coping with the imminent threat, even if it means letting their body temperature change a little.”  
 
To test their idea, Tabh and co-author Mariah Hartjes, a former Biology student at Trent, worked with Biology professor Dr. Gary Burness to collate studies on how the body temperature of animals changed under stress. Their data covered more than 60 years of research and 20 animal species, from eastern chipmunks to ostriches. They discovered there was a tendency for animals to let their body temperatures drift with their surroundings when under stress - either rising in the warmth or falling in the cold.  

Consistent with their idea, animals that spend the most on keeping cool or warm, such as tiny songbirds, cooled by almost five degrees when stressed. In contrast, large species such as cattle, with plenty of surplus energy, showed little temperature change. 

These findings, recently published in Proceedings of the Royal Society of London, provide new insight on how animals balance and prioritize their energy use. By letting their body temperatures drift, energy can be preserved for higher priority tasks, such as defending territories or weathering social threats.