Simplify the following text for a Grade 8 native English-speaking person.
Original: The willow grouse ( Europe ) or Willow Ptarmigan ( North America ) , Lagopus lagopus , is a medium-sized gamebird in the grouse family .
Simplified: The Willow Grouse ( Lagopus lagopus ) or Willow Ptarmigan is a bird of the grouse subfamily .