Bloodsail Admiral's Hat is a cloth headpiece that gives a bonus to stamina. It is part of the coveted Bloodsail "set". It also summons and dismisses a Blood Parrot, Companion, which will not aid you in battle.
This item is a reward from the Bloodsail Buccaneers quest  which starts with Fleet Master Firallon aboard his ship off the southern coast of Stranglethorn Vale. To complete the quest, you must kill Baron Revilgaz and Fleet Master Seahorn in Booty Bay.