Sleeping Birds Graphical Abstract (IMAGE) Cell Press Caption This graphical abstract shows that migratory warblers sleep mostly with the head tucked under the feathers when they are in poor condition, conserving energy but exposing them to a higher risk of predation. Credit Ferretti et al./<i>Current Biology</i> Usage Restrictions Credit Required License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.