Thermal imbalance drives avian performance and responses to climate warming.

Thermal imbalance, measured by net sensible heat flux (Q), predicts performance and geographic limits in endotherms, explaining variation in reproductive success and climate responses.

• Why it matters: Understanding how endotherms respond to climate warming is limited because thermoregulation decouples body temperature from ambient temperature, making existing models less effective.
• What they did: The study developed theory and empirical evidence using biophysical simulations in tree swallows, demonstrating that performance varies predictably with Q, an index of thermoregulatory imbalance, across multiple performance metrics.
• The result: Findings suggest Q constrains performance and shapes breeding ranges in North American birds, providing a new framework to forecast endotherm responses to climate change.