 Rectrices ( from the Latin for " helmsman " ) , which help the bird to brake and steer in flight , lie in a single horizontal row on the rear margin of the anatomic tail . Only the central pair are attached ( via ligaments ) to the tail bones ; the remaining rectrices are embedded into the rectricial bulbs , complex structures of fat and muscle that surround those bones . Rectrices are always paired , with a vast majority of species having six pairs . They are absent in grebes and some ratites , and greatly reduced in size in penguins . Many grouse species have more than 12 rectrices . Some species ( including ruffed grouse , hazel grouse and common snipe ) have a number that varies among individuals . Domestic pigeons have a highly variable number , due to centuries of selective breeding . 
