Cost of carrying radio transmitters: A test with racing pigeons Columba livia

We tested the impact of two types of radio transmitters on flight performance in racing pigeons Columba livia. Prior to each of two flights of known distance, 60 birds were randomly selected from three flocks and put into one of three groups: control, 5-g (i.e. 1.1% of body weight) tail-mounted radios or 8-g (i.e. 1.8% of body weight) sacral-mounted radios. The design of the sacral attachments changed between races as the initial harness caused lesions. Birds with sacral-mounted radios flew more slowly and lost more weight and condition than the other groups. Birds fitted with tail-mounted radios performed similarly to the control group. Loss of condition was correlated with a decrease in flight velocity. We conclude that small tail-mounted radios carry little cost, but sacral mounts may bias results and may be inappropriate for some ecological studies.