Hawk Grass is an item from The Legend of Zelda: Twilight Princess. This oddly shaped grass, whose shape is similar to that of a hawk in flight, grows in extant locations. The function of Hawk Grass is similar to that of Horse Grass; it can be used to summon hawks. While needed very rarely during the course of the game, hawks are useful for gathering hard-to-reach items. It is essential for the recovery of the cradle, without which Link cannot acquire the Fishing Rod and advance in the game.
Wolf Link can use Hawk Grass to Howl the song (similar to Horse Grass and Howling Stones) and summon a Hawk, who will tell Wolf Link if their are any secrets nearby (such as Treasure Chests or Piece of Heart). If Link has collected every thing in that area, the Hawk will tell him there is nothing there.
Hawk Grass can also optionally be used to recover Bee Larva. When Link picks the plant and blows through it, a hawk will circle around for a moment before coming to land on Link's arm. Hanch uses a hawk to drive away Link in his wolf form early on in the game. Interestingly, if Wolf Link uses to summon the Hawk Grass after scaring away Hanch, the Hawk will apologize for attacking him.
Hawk Grass is located in various locations, such as Ordon Village, Death Mountain, Sacred Grove and Lake Hylia. Also, Rusl seems to be able to whistle the tune without a reed, as he did when calling the Golden Cucco and later on when he summoned a hawk in Hyrule Castle.