A study published on Monday in Current Biology revealed that migrating warblers manage the dangers of their long journeys by adjusting their sleep postures to meet their physiological needs.

Plump, well-muscled birds tend to sleep with their heads held upright, while scrawnier warblers tuck their heads into their feathers, a posture that makes them more vulnerable to predation but helps them conserve their much needed energy.

“Migratory warblers have to make trade-offs between staying safe and saving energy,” said Leonida Fusani, a behavioral physiologist at the University of Vienna and the lead author of the paper.

Get the full story at nytimes.com.