This dataset consists of .deg and .lux files as raw data from light-level geolocators (GLS loggers, model: INTIGEO-W30A9-SEA-NOT, 15x5x4 mm, ~ 0.45 g, Migrate Technology Ltd, Cambridge, UK) along with a data table. GLS loggers were attached to seven Wilson's Storm-petrels Oceanites oceanicus and one Black-bellied Storm-petrel Fregetta tropica, caught in February and March 2023 at their nests at a mixed breeding colony near the Argentine Station 'Carlini' on King George Island /25 de Mayo Island, South Shetland Islands within the ice-free area of the Potter Peninsula (62°14'S, 58°40'W). Additional information on the tagged individuals is provided in the data table. The GLS loggers, set to UTC time, had two types of sensors, namely light (data used for geolocation, ".lux-file") and conductivity (wet/dry, i.e. immersion in saltwater, data used for activity, ".deg-file"). Light intensity (0.320 to 74000 lux) was sampled every minute with the maximum value recorded in each five-minute period. The saltwater immersion check was performed every 30 seconds with the number of samples classified as 'wet' (conductivity >63) recorded every 10 minutes, resulting in values from 0 to 20. These logger settings correspond to the manufacturer mode 'W30-6'. After recapture (December 2023 to January 2025), raw data were downloaded from the loggers using IntigeoIF v1.15 software (Migrate Technology Ltd, Cambridge, UK). Two loggers (Bird IDs: BBSP24_17 and WSP23_11) had to be sent to the manufacturer for data download. The main objective of the tracking study was to provide a first insight into the spatial ecology and pelagic activity patterns of the two Antarctic storm-petrel species outside their breeding season. Lisovski et al. (2020) suggests some options how to convert data from GLS loggers into position estimates. Data were collected as part of a research project funded by the DFG priority program Antarctic Research with Comparative Investigations in Arctic Ice Areas (SPP1158).

One .deg-file per individual, with the first 20 lines containing general and logger-specific descriptions of the manufacturer. These are followed by a header line for the data (Date in DD/MM/YYYY, UTC Time in HH:MM:SS and wet counts with values from 0 to 20).--One .lux-file per individual, with the first 20 lines containing general and logger-specific descriptions of the manufacturer. These are followed by a header line for the data (Date in DD/MM/YYYY, UTC Time in HH:MM:SS and light intensity in lux).