Northern Prairie Wildlife Research Center
Clark S. Winchell, U.S. Fish and Wildlife Service, Ecological Services, Carlsbad Field Office, Carlsbad, CA 92008 USA, Timothy A. Burr, Natural Resources Branch, U.S. Navy Southwest Division, NAVFACENGCOM, 1220 Pacific Highway, San Diego, CA 92132 USA, and Nancy C. Harvey, Center for Reproduction of Endangered Species, Zoological Society of San Diego, P.O. Box 551, San Diego, CA 92112 USA
Radio telemetry is an extremely useful tool to study dispersal routes, home range, and mortality factors, as well as numerous other parameters affecting the distribution of animals. Many times the ability to obtain these data variables is limited, as the size and weight of a radio transmitter can influence behavior. This is particularly true for small passerine birds with body weights less than 80 g. Guidelines issued by the Bird Band Laboratory (USGS-BRD) prohibit transmitter weight to exceed 3% of total body weight. We reviewed various transmitter configurations, methods of attachment and evaluated the 3% limit. Our objectives were to design an attachment method using current radio telemetry technology, evaluate its effectiveness on shrikes, and determine any impacts on behavior. Four attachment methods and two transmitter weights (from 3% to 8% of body weight) were evaluated in a captive environment to assess impacts to bird behavior. Attachment method and transmitter weight did not affect EAT or HOP, but did significantly affect FLY (P = 0.001) and PREEN (P = 0.001), behaviors which could increase mortality rates in wild birds. A tail-mounted 1.6-g transmitter proved to be the most accepted with the least effect on individual behavior. Individual compatibility and behavioral factors should be considered when implementing a radio telemetry program on small passerine birds.