There are more than 9,800 known species of birds, but what makes a bird, a bird? 🤔These 4 traits: 1. Warm-blooded 2. Egg-laying 🥚 3. Vertebrate (have a backbone) 4. Feathers Flock to see our 5 aviaries with birds from around the world. 🌍 #BirdNerd #Birding #Aviary #BirdBrain #SanDiegoZoo (📷s by Ian Gill)