qT=2&tQ=All birds...&tC=lay eggs.|have feathers.|are endothermic (warm-blooded).|have a backbone.|all of the above.&cC=5&fB=All birds have feathers, lay eggs, are warm-blooded, and have a backbone. Some birds' bones are hollow to enable them to fly with greater ease.<br><br>In addition, all birds have forelimbs that have evolved into wings. While most birds can fly, some can only travel on foot. 