• Vickery, Peter D.
  UMaine Wildlife Dept.
  
• Hunter Jr., Malcolm L.
  UMaine Wildlife Dept.
  

The absence of adequate song perches has been considered a prmiary factor that may limit use of potential habitat by open country and grassland birds. If the "song perch limitation" hypothesis is correct, it could have important conservation implications because populations of many grassland bird species have been declining throughout North America.