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 <code>datapackage.json</code>. Files are structured as a Frictionless Data Package . You can access all data in R via <code>https://zenodo.org/records/12621787/files/datapackage.json</code> using frictionless . datapackage.json : technical description of the data files. DELTATRACK-reference-data.csv : reference data about the animals, tags and deployments. DELTATRACK-gps-yyyy.csv.gz : GPS data recorded by the tags, grouped by year. Acknowledgements This dataset was collected by the Research Institute for Nature and Forest (INBO), Waardenburg Ecology, Buijs Eco Consult and Deltamilieu Projecten. Funding was provided by the Wozep programme of Rijkswaterstaat on behalf of the Ministry of Economic Affairs of the Netherlands. All datasets from Wozep will be made publicly available, unless stated otherwise. ; This version adds data from 2023and references the latest Movebank Attribute Dictionary.