Some populations do wander southward to warmer temperatures and better food sources, moving diurnally in small feeding flocks. These agile acrobats are often seen hanging upside down to reach the seed heads of grasses, weeds, and shrubs; birch, alder, and willows catkins, as well as tender leaves and buds. During nesting season they add the protein of insects, and feed them to their young. In alternating years they may descend on food sources in large flocking irruptions when seeds, especially birch seeds, dwindle in their usual feeding grounds.
Therr sociability continues while breeding, nesting in loosely spaced groups, low in shrubs or trees, on the ground, or occasionally in cavities in trees or terrain. In a race with temperature, they are a quick-breeding bird, reusing nests or constructing new ones in as little as two days. The female is the builder, using twigs or grassy plant materials to form the framework of the cup, then lining it with the insulating softness of fine grass, willow cotton, caribou hair, vole fur, or ptarmigan feathers.
Males feed the incubating females (sightings of one being fed by more than one male raise the question of their mating system). Using the warmth of a brood patch, she incubates seven pale-blue or greenish-blue spotted eggs, for ten to fourteen days. The altricial hatchlings grow fast, fledging in twelve to fifteen days, but stay with the family flock until it is time to wander.
Since so little of their breeding territory is habitable by humans, Hoary Redpolls are not in danger of its loss. When they are close to civilization these endearing, snowball-shaped birds can be are quite inquisitive, and are regular visitors to bird feeders.