Modern birds are technically theropod dinosaurs that survived the asteroid. They've been refining the flight strategy for 150 million years.
Every chicken, sparrow, eagle, and penguin alive today descends from theropod dinosaurs — the same family as Tyrannosaurus. The asteroid 66 million years ago wiped out most of the dinosaur lineage, but a small group of feathered survivors radiated into the 10,000+ bird species alive today.
Birds have hollow bones, four-chambered hearts, beaks tuned for specific foods, and senses no mammal can match. Pigeons can detect magnetic fields. Owls can pinpoint a mouse's position to within inches in total darkness.
These verified facts cover bird flight, intelligence, migration, the survivors of the K-Pg extinction, and the surprising behaviors that put them on par with primates for problem-solving.
Below: every fact from our verified archive that touches this topic. Each is independently sourced; click through to its dedicated page.