The Siltwing Albatross was a new mount added to WoW in patch 8.1, and it is currently the only albatross mount in the game. So this is the mount you want to go for if you ever dreamed of flying on a big albatross in Azeroth!
This mount is tied to Island Expeditions, but it is not a random drop from them like most of the Island Expedition mounts. Instead you are able to purchase the Siltwing Albatross from a vendor right next to the Island Expedition queue table (NPC Captain Klarisa for Alliance, Captain Zen'taga for Horde).
The cost of the mount is 1,000 Seafarer's Dubloons, a currency that you obtain by doing Island Expeditions. The mount can be bought by any level 20+ character, and used by all characters on your account.
Each Island Expedition win awards you between 1 and 30 Dubloons, so it might take a long time to get 1,000 of these. You have to obtain all thousand of them on a single character, since you are unable to send currency items to your other characters.