DELTATRACK - Herring gulls (Larus argentatus, Laridae) and lesser black-backed gulls (Larus fuscus, Laridae) breeding at Neeltje Jans (Netherlands) is a bird tracking dataset published by the Research Institute for Nature and Forest (INBO). It contains animal tracking data for the project/study DELTATRACK, using trackers developed by Ornitela (https://www.ornitela.com). The study has been operational since 2020. In total 99 individuals of European herring gull (Larus argentatus) and lesser black-backed gull (Larus fuscus) have been tagged in the breeding colony at Neeltje Jans in the Netherlands, mainly to study their use of offshore waters near the Borssele windpark. Data are automatically synced with Movebank and from there periodically archived on Zenodo (see https://github.com/inbo/bird-tracking). Files Data in this package are exported from Movebank study 1258895879. Fields in the data follow the Movebank Attribute Dictionary and are described in datapackage.json. Files are structured as a Frictionless ... : This version adds data from 2023 and references the latest Movebank Attribute Dictionary. ...