GPS fix‐loss alone cannot serve as a reliable proxy for nest attendance in burrow‐nesting birds

GPS fix‐loss is inevitable in biologging studies and is typically treated as random missing data, conventionally excluded or interpolated in subsequent analyses. However, the cause of positioning failure may be linked to behavioural and habitat features; therefore, we tested whether GPS fix‐loss could reveal the nest attendance pattern in the burrow‐nesting Blue‐tailed Bee‐eater Merops philippinus by using GPS‐VHF loggers with onboard light sensors to ground truth. While fix‐loss successfully identified 97.5% of in‐nest events, it resulted in a large number of false positives, that is, invalid GPS attempts with high light intensity. This lack of specificity yielded a low positive predictive value of 19.2% and slight overall agreement (Cohen's Kappa = 0.15) between GPS and light sensor approaches, demonstrating that fix‐loss cannot serve as a reliable standalone proxy for nest attendance in urban breeding Blue‐tailed Bee‐eaters. Nevertheless, recognizing the non‐random nature of positioning failures highlights the need for caution when interpreting missing data in biologging studies.