implantation reduces the negative effects of biologging devices on birds animalborne logging or telemetry devices are widely used for measurements of physiological and movement data from freeliving animals for such measurements to be relevant however it is essential that the devices themselves do not affect the data of interest a recent metaanalysis reported an overall negative effect of these devices on the birds that bear them ie on nesting productivity clutch size nest initiation date offspring quality body condition flying ability foraging behaviours energy expenditure and survival rate method of attachment harness collar glue anchor implant breastmounted or tailmount had no influence on the strength of these effects but anchored and implanted transmitters had the highest reported rates of deviceinduced mortality furthermore external devices but not internal devices caused an increase in deviceinduced behaviour comfort behaviours such as preening fluffing and stretching and unrest activities including unquantifiable active behaviours these findings suggest that with the exception of deviceinduced behaviour external attachment is preferable to implantation in the present study we undertake a metaanalysis of 183 estimates of device impact from 39 studies of 36 species of bird designed to explicitly compare the effects of externally attached and surgically implanted devices on a range of traits including condition energy expenditure and reproduction in contrast to a previous study we demonstrate that externally attached devices have a consistent detrimental effect ie negative influences on body condition reproduction metabolism and survival whereas implanted devices have no consistent effect we also show that the magnitude of the negative effect of externally attached devices decreases with time we therefore conclude that device implantation is preferable to external attachment providing that the risk of mortality associated with the anaesthesia and surgery required for implantation can be mitigated we recommend that studies employing external devices use devices that can be borne for long periods and wherever possible deploy devices in advance of the time period of interest