Greenskin Military Messenger Crow

Used exclusively by Greenskin tribes and civilizations, the Military Messenger Crow is a horse sized black bird that can carry supplies, notes, and can relay short messages back and fourth between senders. Generally a hundred words is the most they can repeat, and they have to make it to their destination within three days or else they'll forget how to repeat the message. 
The only combat capabilities they possess is the ability to drop large projectiles like rocks or tree trunks. They cannot throw or toss, but they can drop. Its also possible to equip them with a beast master and up to three archers. The thicker the bird is, the more they can carry. 
Another use for the Military Messenger Crow is to deliver supplies to and from camps, cities and battlefields. They are predictible animals who have no problems listening to orders and commands. They are loyal to their masters and always return. 
While the birds have their own personalities, its rare to find a bird who will disobey or go off on their own adventures. These defective birds are dubbed "damaged", and are generally killed upon returning to their respective militaries. There have been a few times where Damaged Crows were set free, only for them to become dangerous to ecosystems, villages and other civilizations. As soon as they become feral, they start to cause as much havok on the lands as a dragon does.