By mid November, the high-pitched, squeaky calls of Townsend's solitaires are echoing across our Littleton, Colorado, farm. Summer residents of the upper foothills and mountain forests, many descend to lower elevations during the colder months and their fondness for juniper berries brings a few to our property.
Resembling streamlined, gray robins with white eye rings, solitaires typically call from the top of trees; were it not for those distinctive calls, they might otherwise go unnoticed, picking their way among the junipers to feast on their fruit. They will generally remain in the lower foothills and on the piedmont through March before returning to their breeding grounds at elevations of 7500 to 11,000 feet.
This behavior, known as vertical migration , is common among birds that inhabit mountainous landscapes. Among the other mountain residents that turn up on our farm (elevation 5400 feet) in winter are gray-headed juncos, mountain chickadees and Cassin's finches; less common visitors include red crossbills, pine grosbeaks and Steller's jays.