FORT WORTH -- Kujo perched on a tree branch in downtown's Burnett Plaza, warily watching for prey.No grackles or starlings were in sight.Instead, a man raised his arm.Kujo, a 2-year-old Harris's hawk, quickly flew low and fast through the chilly morning air to reach the outstretched arm of Roger Crandall, his handler.Rewarded with pieces of mouse meat, he knew that next time, his bounty could be bigger.Kujo and his working mate, Blackjack, could be the newest tools in the city's efforts to drive out grackles -- long known as "downtown's feathered menace."Recent changes in federal law, prompted by local falconers...