Winter ecology of the partridge (Perdix perdix) in the Canadian prairie

[Summary...]
Partridges (Perdix perdix) were introduced into the Canadian prairie in 1908 and have acclimatized successfully in spite of rigorous winters.
They are morphologically well adapted to exist in cold winters with limited snow: long enough legs and favourable weight load, heavier winter plumage, layers of fat acting as insulation as well as emergency energy. Partridges respond to winter with extreme economy in energy: they never fly unless forced to, and when not feeding sit still with ruffled feathers, tarsi covered, beak among shoulder feathers to breathe pre-warmed air. They roost in a huddle ("jug") on hard snow or in holes in loose snow. Throughout winter they live in coveys, with security against predators.
The major factor in successful winter survival of partridges in the prairies is their change in food habits. In Europe they feed mainly on green leaf material during winter, while in the prairies partridges feed almost exclusively on waste grain and weed seeds. During zero weather a partridge consumes daily some 50-75 g. of grain and weed seeds to maintain body temperature, and only this high calorific food can sustain them; green foliage would require four times the bulk to yield the same number of calories, and could not be obtained or stored and utilized in crop and gizzard in the time available. Both waste grain and weed seeds keep intact, not rotting or germinating in the dry snow in temperatures almost constantly below freezing. So there is an abundant food supply, readily available.