Loss from Harlequin Ducks of abdominally implanted radio transmitters equipped with percutaneous antennas

We documented extrusion and loss of abdominally implanted radio transmitter s with percutaneous antennas from adult female Harlequin Ducks (Histrionicu s histrionicus). Birds were captured during wing molt (late August to mid-S eptember) in 1995-1997. Of 44 Harlequin Ducks implanted with radios and rec aptured, 7 (16%) had lost their transmitters and 5 (11%) had radios in the process of extruding. Most (11 of 12) extrusions and losses occurred in bir ds implanted with radios in 1996 and recaptured in 1997. We suggest that tr ansmitter extrusions and losses were due largely to changes in transmitter design made between 1995 and 1996. Transmitters implanted in 1996 were cyli ndrical rather than spherical, had a flat end with an abrupt edge, and the lower portion of the antenna was reinforced. Radio losses occurred after th e 7-mo monitoring period and caused no apparent harm to the birds. Investig ators using implanted radios with percutaneous antennas for long-term proje cts should be aware of the potential for radio extrusion and should minimiz e the problem by using transmitters that have no sharp edges and that are w ide, rather than narrow.