You enjoy a +4 dodge bonus to Armor Class against all ranged attacks in a round in which you move at least 10 feet, or in any circumstance in which you have cover. You must be aware of the attack to gain this bonus.
A condition that makes you lose your Dexterity bonus to Armor Class also makes you lose dodge bonuses like this one. Also, note that dodge bonuses stack with each other, unlike most other types of bonus.