The Digestion and Intake of Winter Foods by Wild Ptarmigan in Alaska

Abstract

This paper describes a method for measuring the digestibility, metabolizable energy, and daily intake of foods eaten by wild ptarmigan in winter, using the magnesium which occurs naturally in the food as a digestibility marker. This method has already been tested on captive Red Grouse (Lagopus lagopus scoticus) (Moss and Parkinson 1972). Further laboratory tests with captive Rock Ptarmigan (Lagopus m&us) are now presented together with winter energy budgets of free-living Willow ( Lagopus lagopus), Rock, and White-tailed (Lagopus leucurus) Ptarmigan in Alaska. METHODS EXPERIMENTS WITH CAPTIVES Most of the work on captive birds was done in Scotland during the winter when birds were not molting, laying, or growing. Rock Ptarmigan hatched from eggs collected in the wild in Scotland and reared (Moss 1969) in captivity were used.