qT=1&tQ=When birds feel threatened, they...&tC=sleep with one eye open.|don't sleep.|sleep with both eyes open.|burrow underground.|shiver.&cC=1&fB=When a sleeping bird senses danger, it alternates which half of its brain is awake and which half is asleep. It also keeps one eye open to watch for predators.<br><br>Birds on the edge of a flock will keep the eye that faces out to the surrounding area open. 