EFFECTS OF RADIO TRANSMITTERS ON MIGRATING WOOD THRUSHES

--We quantified the effects of radio transmitters on Wood Thrushes (Hylocichla mustelina) using 4 yr of banding and telemetry data from Piedmont National Wildlife Refuge, Georgia. Flight performance models suggest that the 1.6-g transmitter shortens the migratory range of wood thrushes by only 60 km, and the estimated migratory range is adequate to accomplish migration even with limited fat stores. We used two strengths of line, 5and 9kg test-strength braided Dacron, to attach the transmitters using the thigh-harness method. We recaptured 13 returning radio-marked wood thrushes, seven of which were still marked. Six of the seven birds marked with the 5-kg test harnesses lost their transmitters within 1 yr while all six of the 9-kg test harnesses were still attached up to 21 mo later. Radio-marking did not reduce the return rates of adults and immatures, and the transmitters did not cause radio-marked birds to lose more mass than banded-only birds. Wood Thrushes can successfully carry a transmitter during migration with no detectable negative effects. We recommend continued use of the thigh-harness method, but we encourage the use of 5-kg cotton line. EFECTO DE LOS RADIOTRANSMISORES EN HYLOC/CHLA MUSTELINA MIGRANTES Sinopsis.--Cuantificamos el efecto de los radiotransmisores en Hylocichla mustelina utilizando 4 aftos de datos de anillaje y de telemetria del Refugio de Vida Silvestre Nacional de Piedmont, en Georgia. Los modelos de desempefio de vuelo sugieren que los radiotransmisores de 1.6-g reducen el alcance migratorio de esta especie por tan solo 60 km, y el alcance migratorio estimado es adecuado para conseguir la migraci6n inclusive con falta de reservas de grasa. Utilizamos lineas de dacr6n entrelazadas y probadas para resistencia de dos potencias de linea, de 5-y 9-kg, para ajustar los radiotransmisores utilizando el m•todo de arnfs de muslo. Recapturamos 13 aves marcadas con radiotransmisores, siete de las cuales estaban todav/a marcadas. Seis de las siete aves marcadas con el arn6s de 5-kg de prueba Current address: Institute of Ecology, University of Georgia, Athens, Georgia 30602.