Main Walkthrough

Location: Martha's Rest
Petitioner: Rowan, Traveling Trader
Unlocked: Complete What a Bird Wants, complete The Gathering Storm
Reward: Ambrosia's Tack, 60 Sharp Fangs, 20 Renown

In order to trigger this side quest you need to complete two prerequisites:
  • First, you need to finish the What a Bird Wants side quest. This is only accessible before you tackle the main story quest The Crystals' Curse, so if you didn't finish it then you're out of luck.
  • Complete the majority of the main story quest The Gathering Storm. Specifically you need to complete the sub-quest Release.
Fulfill those two conditions and The White-Winged Wonder will appear near the southern bridge into Martha's Rest. You can jump right to it by using the Martha's Rest Obelisk.

Check out the spot and you'll find Rowan, the surly trader from What a Bird Wants, yelling to Clive for assistance. He's a bit friendlier this time around, and begs Clive to assist Whiteheart, a white-feathered Chocobo whose flock is being attacked by bandits. Might as well help out.

Leave Martha's Rest via the southern bridge and take a right on the other side. As you head southwest you'll come across a White Chocobo Pinion. Head south from here towards Crooked Nash's Pier, a dead-end clearing on the other side of a bridge. You'll come across a gang of Chocobo Poachers, some melee combatants, some casters. Your Eikonic Abilities will make short work of the first round... 

... though their reinforcements include some Harrier Hounds and a Huntsman, who fights similarly to Gigases and Imperial Champions. The Huntsman has no special attacks, just heavy melee swings with his club, and shouldn't be too much of a threat this far into the game. You'll receive Steelsilk and a Gil Bug for taking him down, and Rowan will show up to provide the rest of the reward.

Chocobo Riding

As a result of saving Whiteheart Clive will receive his own Chocobo mount. Whenever you're in an outdoor area you can press and hold R3 (the right control stick) to summon Whiteheart and her flock. Approach and press the X button to hop on and run around. You can even fight while atop Whiteheart, though the amount of damage you do compared to fighting as Clive is... paltry. Still, when it comes to moving swiftly across open terrain, riding Whiteheart is second to none.