Are you using geolocators? You will want to check out this review!!
“…Use of geologgers on small birds has great potential to help address major research and conservation questions, but the method is not without its shortcomings. …We examined return rates of birds with geologgers in published and unpublished studies and found no evidence of a general negative effect of geologgers on survival, although there were a few individual studies where such an effect was evident…. With regard to analysis methods, we believe there is much room for improvement. Use of online archiving of both data and analysis parameters would greatly improve the repeatability and transparency of geologger research.”
Eli Bridge and friends just published a review of tracking birds with light level geolocators.