Peer Reviewed Comparison of the Effects and Performance of Four Types of Radiotransmitters for Use With Scoters S. A. IVERSON, Centre for Wildlife Ecology, Simon Fraser University, Delta, BC V4K 3N2, Canada W. S. BOYD, 1 Canadian Wildlife Service, Pacific Wildlife Research Centre, Delta, BC V4K 3N2, Canada D. ESLER, Centre for Wildlife Ecology, Simon Fraser University, Delta, BC V4K 3N2, Canada D. M. MULCAHY, United States Geological Survey, Alaska Biological Science Center, Anchorage, AK 99503, USA T. D. BOWMAN, United States Fish and Wildlife Service, Anchorage, AK 99503, USA Abstract Radiotransmitters are widely used in wildlife ecology, often providing data that cannot be collected using other methods. However, negative effects have been associated with the use of transmitters for some species. We evaluated the effects and performance of 4 radiotransmitter types for use with surf and white-winged scoters (Melanitta perspicillata and M. fusca): COEXT—coelomically implanted transmitters with external antennas, COINT—coelomically implanted transmitters with internal antennas, SUBCU—subcutaneous implants with external antennas, and PRONG—external mounts, attached by a subcutaneous anchor and glue, with external antennas. Survival was not related to radiotransmitter type during the immediate (14-d) post-release period when most deaths (8 of 12) occurred. Rates of signal disappearance (transmitters ceased to be detected in the study area) and transmitter shedding (transmitters recovered without sign of predation) were similar among types over 30- and 60-day intervals; however, higher proportions of dorsally mounted radiotransmitters (SUBCU, PRONG) disappeared or were shed over course of the full 100-day monitoring period used in this study. All 4 radiotransmitter types allowed for relatively accurate location estimates, with linear error estimates (distance between actual and estimated location) averaging ,50 m when receivers were within 1 km of transmitters. However, signal strength was lower for COINT transmitters. Based on our results, we recommend COEXT transmitters for radiotelemetry studies .2 months in duration and for satellite telemetry studies of scoters. However, SUBCU and PRONG are recommended as cost-effective alternatives in shorter-duration radiotelemetry studies. (WILDLIFE SOCIETY BULLETIN 34(3):656–663; 2006) Key words coelomic implant, location error, Melanitta fusca, Melanitta perspicillata, radiotelemetry, radiotransmitter retention, sea duck, surf scoter, survival, white-winged scoter. Radiotransmitters provide valuable information about animal movements, resource use, and population demography difficult to collect by other means (White and Garrott 1990). Historically, a variety of attachment techniques have been used with differing degrees of success. However, general guidelines for selecting radio packages and attachment procedures are difficult to establish because wildlife taxa do not respond uniformly to tagging (Withey et al. 2001). Two main factors biologists must consider when choosing a method of attaching transmitters to study animals are 1) the transmitter must not unduly harm the study animal or affect its behavior in a way that would bias data collection, and 2) the attachment must be secure, so that the transmitter remains on the study animal for the duration of the study period (Pietz et al. 1995). Among waterfowl, deleterious effects have been associated with radiotransmitters, particularly those attached externally. Negative effects include reduced survival and return rates (Ward and Flint 1995, Dzus and Clark 1996, Paquette et al. 1997); behavioral changes (Greenwood and Sargeant 1973, Pietz et al. 1993); higher predation rates and susceptibility to harvest (Wheeler 1991, Blouin et al. 1999); and reduced fecundity as a result of lowered nesting propensity, delayed nest initiation, and smaller clutch sizes (Pietz et al. 1993, Rotella et al. 1993, Paquette et al. 1997). Diving birds, in particular, appear susceptible to deleterious effects of externally attached transmitters, with entanglement in submerged vegetation, hydrodynamic drag, and increased metabolic costs related to thermoregulation noted as potential problems (Wilson et al. 1986, Korschgen 1996b). Recently, surgical implantation of transmitters into the coelomic cavity (commonly referred to as the abdominal cavity) has been employed as an alternative to external mounts for several waterfowl and diving bird species (Korschgen et al. 1984, 1996a, Olsen et al. 1992, Mulcahy et al. 1999). Fewer negative effects have been reported for coelomically implanted radio packages (Hupp et al. 2003), suggesting that internal implants may provide a superior alternative for telemetry studies of diving birds (Esler et al. 2000a). Coelomically implanted radios with external antennas have been used successfully with species such as the harlequin duck (Histrionicus histrionicus; Mulcahy and Esler 1999, Mulcahy et al. 1999, Esler et al. 2000a); however, other taxa have suffered negative effects from this type of transmitter. For example, common and thick-billed murres (Uria aalge and U. lomvia) and tufted puffins (Fratercula cirrhata) outfitted with coelomically implanted satellite transmitters exhibited reduced reproductive effort (Meyers et al. 1998) and postsurgery mortality rates in excess of 50% (Hatch et al. 2000). In this study, we compared the effects and performance of 4 types of radiotransmitters for use with surf and white-winged scoters (Melanitta perspicillata and M. fusca) wintering in coastal British Columbia, Canada. Scoters are closely related to harlequin ducks phylogenetically (Livezey 1995) and share several key natural history characteristics, including diving for prey, suggest- ing that they would respond similarly to coelomic implants. However, preliminary research indicated that, unlike harlequin 1 E-mail: Sean.Boyd@ec.gc.ca 656 Wildlife Society Bulletin  34(3)