The Harlequin Duck (Histrionicus histrionicus) is a small sea duck, which travels inland to breed on fresh water streams. Harlequins breed in western North America from Alaska and the Yukon south through western Montana to California (Harlequin Duck Working Group 1993); in eastern North America, they breed from Baffin Island south to eastern Quebec and Labrador (Goudie 1993). In the Palaearctic, they breed in Iceland, Greenland and Siberia (A.O.U. 1983). Approximately 110-150 pairs of Harlequins currently breed in Montana (Reichel and Genter 1994), with most located in the following areas: 1) tributaries of the lower Clark Fork River; 2) tributaries of the North, Middle, and South forks of the Flathead river; 3) streams coming off the east front of the Rocky Mountains; and 4) the boulder River (Miller 1988, 1989, Kerr 1989, Carlson 1990, Fairman And Miller 1990, Diamond and Finnegan 1992,1993). During the breeding season, Harlequins are found along fast mountain streams (Bengston 1966). In many areas, harlequins use streams with dense timber or shrubs on the banks (Cassirer and Groves 1990), but they are also found in relatively open streams along the east slope of the Rocky Mountains, Montana (Markum and Genter 1990, Diamond and Finnegan 1992), and the arctic tundra (Bengston 1972). In Idaho, 90% of observations occurred near old growth or mature timber stands (Cassirer and Groves 1990). Mid-stream rocks, logs, islands, or stream-side gravel bars serve as safe loafing sites and appear to be important habitat components. Most of the ducks arrive on their inland breeding areas in mid-April to early May; unmated males typically arrive before pairs (Kuchel 1977). The females and young remain on the streams until August or early September. This chronology is influenced by elevation and by the timing of spring runoff, it may vary up to several weeks between years. The U.S. Forest Service, Region 1, lists the Harlequin Duck as Sensitive (Reel et al 1989). The species is listed as a Species of Concern by the Montana (Montana Natural Heritage Program 1994) and Idaho (Idaho Conservation Data Center 1994) Natural Heritage Programs. The eastern and western populations are both listed under Category 2 as candidates for protection under the Endangered Species Act by the U. S. Fish and Wildlife Service (U.S. Department of Interior 1991). The Montana Natural Heritage Program began surveying Harlequin Ducks in 1988. The survey data gave rise to questions involving site fidelity, productivity and mortality. We began individually marking Harlequins to a limited extent in 1991; through 1995, a total of 249 Harlequins were marked on 9 streams, representing the largest population of marked Harlequins from breeding streams. Birds marked in Montana have subsequently been captured and observed on the coasts of Oregon, Washington and British Columbia, with most reports coming from Vancouver Island. During that time, we observed 20 previously marked adults returning to Montana streams.