Owl post

From Harry Potter Wiki

Owl post is a system of sending messages or items using owls as the carriers. Besides the Owl Post Office, individuals and organizations with their own owls use them as their mail bearers. Harry Potter's owl, Hedwig was used as his primary means of communicating with his friends and his godfather, Sirius Black. Hogwarts School of Witchcraft and Wizardry had a number of owls that anyone at the school could use. They, along with students' personal owls, were kept in the Owlery.

Post owls are quite intelligent, and can usually find their mail's recipient with little to no direction.

Other birds can be used for delivering messages. Sirius Black, while in hiding, sent used unspecified tropical birds as message carriers while communicating with Harry Potter, leading Harry to speculate that Sirius was hiding in a warmer environment than England. However, the preponderant bird used for messaging was the owl.