Null effects of the Garcelon harnessing method and transmitter type on soaring raptors

Abstract

Tagging wildlife with transmitters is one of the most widely used techniques for research and monitoring. Knowing the possible impact of attaching transmitters to an animal has always concerned researchers; however, most assessments have been directed at the effects of transmitters on behaviour and fitness, and fewer have addressed possible injuries to the individuals. The present study evaluated the physical status of birds tagged with transmitters mounted with a Garcelon‐type backpack harness, from five species of large and medium‐sized soaring raptors in western Europe. The study also assessed the factors determining their duration and outcomes. We sent a survey to the managers of projects involving tagged raptors over a 24‐year period, concerning tracking results and veterinary analyses. We obtained information on 659 birds, of which 196 included clinical evaluation from birds in hand. None of the birds showed marks, injuries or abrasions on their feathers or skin caused by the harness or the transmitter. Therefore, this deployment technique is recommended for soaring birds in general and for others in which the use of a backpack harness is chosen. The duration of the system on the bird depended on the traits of the transmitter, being greater in platform transmitter terminal (PTT) satellites. The device lasted longer in larger species and for a shorter time when tagging nestlings. We propose the need for nestlings to be fitted with harnesses corresponding to the size of their adult conspecifics, distinguishing between males and females. Otherwise, the differential growth between sexes could cause discomfort and more frequent removal attempts of the harness. Our results are especially useful for managers and ethics committees to assess bird welfare risks before issuing official permits.