This very public and confrontational tactic is somewhat unusual for the Humane Society of the United States, an influential animal welfare group, which prefers to work with companies behind the scenes, Balk said. But the humane society and several other animal rights groups are frustrated. They want Chicago-based McDonald’s, the largest restaurant company in the world, to commit to changing to different breeds of chickens, possibly slower-growing birds that would have healthier lives, as well as giving them more space.