The science of conservation biology and the practice of wildlife management depend upon long-term databases, but collecting such data can be difficult, expensive, and labor intensive. Conservation biologists and wildlife managers have long used nonprofessional volunteers to collect much of the information needed to make informed decisions concerning the resources they are attempting to understand and protect. The advent of the modern field guide in the 1930s, together with the growing availability of prismatic binoculars, heralded the modern age of recreational bird watching. Since then, bird watchers have made significant and substantial contributions to our understanding of bird populations in North America. Hawk Mountain Sanctuary in eastern Pennsylvania has used volunteer hawk watchers, in conjunction with its own paid staff, to help create the longest and most complete record of raptor migration in the world. The Sanctuary's annual counts of migrating raptors have proved a critical resource in assessing long-term trends of raptor populations in northeastem North America. The extensive database played a key role in exposing the threat of organochlorine pesticides to bald eagles (Haliaeetus leucocephalus) and other predatory birds earlier this century, as well as in tracking more recent recoveries in many of the same populations. Recent analyses of the database are yielding insights into (1) how cold fronts affect counts of raptors at migration watchsites, (2) the extent to which climate change affects the timing of raptor migration, and (3) changes in the migratory habits of sharp-shinned hawks (Accipiter striatus) in eastern North America. I submit that volunteers will play increasingly important roles in wildlife conservation wherever their efforts can be coupled with those of professional practitioners in the field.