Modified method for external attachment of transmitters to birds using two subcutaneous anchors

Of the transmitter attachment techniques for birds, the subcutaneous anchor provides a secure attachment that yields relatively few secondary effects. However, the use of subcutaneous anchors has been limited by transmitter size and retention time. Using a modified method of attachment that utilized two subcutaneous anchors, we deployed 69 GPS transmitters, plus 13 VHF transmitters that were similar in size and weight to GPS models, on Pacific Black Brant (Branta bernicla nigricans). Prior to our study, only harnesses were used for attaching GPS transmitters on birds, mainly because GPS transmitters are too large for other external attachment techniques and implantation in the body cavity attenuates the GPS signal. Thus, to increase the size capacity of anchor attachment and to avoid the well‐documented negative effects of harnesses on behavior and survival, we added a second anchor at the transmitter's posterior end. The double‐anchor attachment technique was quickly and easily accomplished in the field, requiring bird handling times of <10 min. Incidental recoveries of tagged Brant indicate a high degree of transmitter retention. Five recaptured birds (4–6 weeks after deployment) and eight killed by hunters (3–6 mo after deployment) retained their GPS transmitters. For studies involving the use of relatively large transmitters, the double‐anchor method appears to provide a viable alternative for external attachment.