Encyclopedia of Life: http://eol.org/pages/1047051/overview
Brief introduction: The Downy Woodpecker (Picoides pubescens (Linnaeus, 1766)) is the smallest of its kind in North America. It uses a number of vocalizations, including a short 'pik' call and produces a slow drumming sound while it pecks into trees compared with other North American woodpeckers.
Zhang et al., Comparative Genomics Reveals Insights into Avian Genome Evolution and Adaptation. Science, (2014).
Jarvis et al., Whole Genome Analyses Resolve Early Branches in the Tree of Life of Modern Birds. Science, (2014).