References
- Bergerud, A., Peters, S. S. & McGrath, R. 1963: Determining sex and age of Willow Ptarmigan in Newfoundland. ). Wildl. Mange. 27, 700–711.
- Weeden, R. B. & Watson, A. 1967: Determining the age of rock ptarmigan in Alaska and Scotland. J. Wild!. Manage. 31, 825–826.