The smallest and one of the most widespread of North American woodpeckers, the Downy Woodpecker is a year-round resident coast to coast and from the tree line in Canada and Alaska to south Florida and the riparian forests of southern California. Audubon (1: 249) commented on its ubiquity and broad habitat tolerance:
"I have found it pretty generally distributed from the lower parts of Louisiana to Labrador, and as far to the westward as I have travelled. It seems, in fact, to accommodate itself to circumstances, and to live contented anywhere."
Although there is evidence of seasonal movements, these are not well understood, seem to involve only a small fraction of any population, and are more likely dispersal than migration. The Downy Woodpecker is equally at home in urban woodlots or more extensive forests and is readily attracted to backyard bird feeders. It is primarily insectivorous, focusing its foraging activities on surfaces, bark crevices, and shallow excavations of trees, shrubs, and woody weeds. Diet and foraging techniques vary with season and sex; indeed, this woodpecker species has become a classic illustration of differential niche use by the sexes: Males tend to forage more on smaller branches, females more on larger branches and trunks of trees.
The Downy Woodpecker varies geographically in size and plumage color and pattern, generally paralleling similar variation in the Hairy Woodpecker (Dryobates villosus), although not as pronounced (2, 3, 4). Sexes of adults are easily distinguished by the presence of a red nape bar in males, which is absent in females.
The Downy Woodpecker is a Linnaean species—named not by an American scientist, but by Carl Von Linne (i.e., Linnaeus), the father of the science of taxonomy. Linnaeus, however, never saw a Downy Woodpecker, instead basing his description (5) on the work of the American colonial naturalist Mark Catesby. It was Catesby who gave the species its common name, with "Downy" a reference to the soft white feathers of the white stripe on the lower back, in contrast to the similar, but more hairlike feathers on the lower back of the Hairy Woodpecker (6). Various authors have suggested (incorrectly or less precisely) alternative meanings: Therres (7) said simply that it was in reference to the soft appearance of its plumage; and Jobling (8) suggested it was a reference to the lesser bristles covering the nostrils of the Downy Woodpecker as compared to those of the Hairy Woodpecker.
In some aspects, such as foraging ecology, the Downy Woodpecker is remarkably well-studied. It has been the focus of several theses, dissertations, and major studies (e.g., 9, 10, 11, 12, 4, 13, 14, 14, 15), although winter foraging ecology has received the greatest emphasis. Some aspects of its breeding biology have been studied in detail, but basic questions, such as whether pairs can raise more than one brood per year or what hatching and fledging rates are, have received little attention. Most detailed ecological studies have been in the northern and eastern United States (e.g., Compton  in New York, and Staebler  in Michigan). Two theses have focused on vocalizations and drumming behavior (18, 19) and there have been 3 major studies of geographic variation (3, 4, JAJ). A popular book on the Downy Woodpecker includes excellent photos of nestlings and adults showing diverse behaviors and presents an overall review of the life history of this appealing species (see Ritchison ) .