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Randy L. Riviere, Gaylord Memorial Laboratory, School of Natural Resources, University of Missouri - Columbia, Puxico, MO 63960 USA, and Kevin P. Kenow, U.S. Geological Survey, Biological Resources Division, Upper Mississippi Science Center, P.O. Box 818, La Crosse, WI 54602 USA

Surgical implantation of radio transmitters provides an alternative attachment technique to surmount complications associated with the placement of external devices on waterfowl (e.g., behavioral changes). Transmitters implanted subcutaneously on the back of newly-hatched ducklings have successfully been used to determine the timing and causes of brood mortality. With minor modification, this technique has also been applied to adult ducks. The method was initially used on a few female canvasbacks (Aythya valisineria) in northwestern Minnesota. Nesting chronology and clutch size of radio-marked canvasbacks did not differ (P > 0.05) from unmarked birds. More recently, 55 female mallards (Anas platyrhynchos) were marked with subcutaneously-implanted transmitters and compared with 49 wild unmarked mallards within the San Joaquin Valley Grasslands Ecological Area, California. No differences (P > 0.05) in clutch size, egg volume, timing of nest initiation, or nest success were observed between the two groups. Our observations suggest that this technique offers a potentially valuable method for radiotelemetry studies of adult ducks. We encourage others to consider subcutaneously-implanted transmitters when conducting experimental comparisons of available attachment methods.