Data from: Migratory and breeding behaviour of Water Rails Rallus aquaticus in east-central Scotland revealed by geolocators

The Water Rail breeding population at the Tay Reedbeds, eastern Scotland, is partially migratory. The aim of the study was to investigate the migratory and breeding behaviours of Water Rails in Scotland’s Tay Reedbeds. Light-level geolocators were used to estimate migration timing, identify non-breeding locations and infer breeding behaviour of nine individuals from ten recovered geolocators over a six-year period. Five breeding birds remained resident year-round, two migrated to Ireland for the winter (including one individual tagged in two years that migrated in both), and two additional birds arrived from north-east Europe to winter in the Tay Reedbeds. Based on incubation periods of ≥19 days as an indicator of success, ten of 15 incubation attempts (67%) were successful. Among the ten bird-years (n = nine individuals, with one bird monitored across two years), 50% of breeding birds were single-brooded, 10% were double-brooded, 20% made a second breeding attempt after a failure, 10% made two failed attempts before a successful one, and 10% made a single unsuccessful attempt. The results indicate that the breeding population of Water Rails in Britain, previously considered resident, is partially migratory. Light-level geolocators can provide valuable insights into breeding ecology, particularly for species where direct observation is challenging.