Radar-based monitoring of marbled murrelets

We used radar to measure daily, monthly, and annual patterns of Marbled Mur relet (Brachyramphus marmoratus) abundance and movements at 12 major river valleys in the Olympic Peninsula of Washington. Landward movements of murre lets peaked from similar to 75 min to similar to 20 min before sunrise, fol lowed by a seaward exodus from similar to 20 min before sunrise to similar to 65 min after sunrise. This general pattern of a landward movement follow ed by a seaward exodus varied little, but the tinting of the seaward exodus gradually became later from May to July. Within a morning, numbers of land ward radar targets averaged twice the numbers of seaward targets, and morni ng counts were approximately five times evening counts. Species identificat ion error rates were lower for landward radar counts than for seaward count s. Radar counts varied through the season, with numbers increasing from May to July, then dropping in August. Seaward counts were more variable than l andward counts. There was wide overlap among months in the amount of daily variation in both landward and seaward counts. Radar appears to be a powerf ul, cost-effective, and non-intrusive tool that can establish an index of a bundance for murrelets at specific inland breeding areas.