They also consume mosses and supplement their menu with insects and spiders when available. They have an uncanny knack of choosing the most nutritious material available, a necessity for meeting their high energy demands. Chicks need a high-protein diet for rapid growth. After eating the yolk sac from which they hatched, they begin to pick up a variety of objects, especially caterpillars, other invertebrates, flowers, and seeds. Winter is the critical time, as the choice and quantity of food are reduced to the few plants found above the snow or in windswept places.
Ptarmigans eat the seeds, buds, and twigs of low willows, alders, and dwarf birches.
To consume the catkins and buds of other trees and shrubs, Willow Ptarmigans have learned to perch, somewhat unsteadily, in thin branches. By contrast, Rock Ptarmigans are adept at scratching in shallow snow to reach buried vegetation such as the ground-hugging purple saxifrage, and they take advantage of feeding craters made by caribou, muskoxen, and arctic hares. White-tailed Ptarmigans supplement their diet with the needles and buds of spruces, pines, and firs. Each species has evolved subtle differences in bill size and shape related to its main winter food. Conservation Ptarmigans as well as snowshoe hares, Ruffed and Spruce grouse, lemmings, lynx, red and arctic foxes, and Snowy Owls are animals that undergo cyclical population fluctuations.