Ravens, focusing on their intelligence.

A bird that spawns in forests, but prefers soaring over plains biomes in the day. They spawn in groups of 2-3 in a nest, which is basically stuck on the side of the tree. If you break the nest, you can find bones, sticks, rotten flesh and arrows, as the ravens are carrion birds and steal bits off dead mobs. If you find a nest, you could also wait instead of breaking it until the ravens come back at night, then tame them with rotten flesh or phantom membrane. Ravens are intelligent birds, and so they are healed with experience points. The perks of owning a raven are that they will fly high above you and swoop down to pick up item drops and fired arrows in their beaks and bring them to you, making them very useful in ranged combat. As their secondary use (like cats bringing items when you sleep or parrots dancing), they are able to assist in combat. If they are carrying any arrows (normal, tipped, spectral) they will, when in combat, attempt to drop it on the enemy mob to damage it. You 'teach' this to the raven by demonstrating hitting a mob with a bow where the raven can see you, and get an achievement called "The Scholar".