Why do flocks of birds gather on snowy roads?

My immediate thought was that they're probably after the salt on the road, and an Internet search confirmed it. According to NH Department of Environmental Services, "Birds, the most sensitive wildlife species to salt, often mistake road salt crystals for seeds or grit. read more

Flocks of such species naturally seek out windswept (and thus snow-cleared) open spaces for fossicking in winter. Plowed road edges provide the same foraging opportunities. In addition, birds need grit in their crop to digest, and roads can be a source for small stones and so forth. read more

In treetop flocks, the leaders are usually chickadees. These busy, acrobatic little birds live in pairs or family groups during the summer, but in winter they gather in groups of a dozen or more. These flocks stick together throughout the cold months. read more

Like the Snow Bunting, Lapland Longspurs breed high in the Arctic and then winter in large flocks, some as many as 4 million strong, in the open fields of the northern U.S. Males are distinctive, with jet-black masks, reddish necks, and a yellow eye stripe. read more