Methodology:

From September 2024 to September 2025, sheathbills were caught and ringed at Bird Island Research Station, South Georgia (54°00'S; 38°03'W). Catching was primarily carried out at Freshwater Beach, Bird Island, where the Research Station is located. However, birds were also caught across several beaches on the south of the island. Methods for catching largely consisted of the use of a hand-net and head/leg noosing.

Once caught, birds were ringed with a metal F (inside diameter: 9mm) or G (inside diameter: 11mm) British Trust for Ornithology (BTO) ring, with Fs being applied to all birds with a tarsus diameter < 8mm. Birds caught as adults were ringed with the metal ring on the right tarsus and known-age chicks on the left tarsus. Birds were also colour banded on the opposite leg using a blue or yellow darvic ring, depending on the location. Zones for darvic colour allocation were determined based on proximity to the Research Station - with blue rings used at the base and along the south and south-western coast of the island, and yellow elsewhere. The first three birds ringed did not receive a darvic as they were part of a pilot study investigating which size of BTO ring would fit.

Once ringed, measurements were taken including: wing length (flattened chord), culmen length (from the tip of the upper mandible to the edge of the feathering at the base of the skull), culmen depth (the maximum depth between the bill without sheath and under the edge of the lower mandible), culmen width (the maximum width of the mandible without the sheath), sheath length (from the edge of the sheath to the edge of the feathering at the base of the skull), sheath depth (the maximum depth between the upper edge of the sheath and under the edge of the lower mandible), tarsus length (the minimum tarsus length), tarsus depth (the maximum depth of the from the anterior to the posterior of the leg) and mass. Field age was recorded using EURING age codes. The EURING age coding system was designed in the northern hemisphere based on the calendar year January to December. For use in the southern hemisphere, where the breeding season occurs at the opposite end of year, it must be adapted. As such, years are considered to begin in June rather than January. Where birds were found to be in moult, moult scores were determined following Bensch and Grahn's standardised methodology (Bensch and Grahn 1993). Primary feathers are assigned a score between 0 and 5 based on their age, which together indicates which stage of moult the bird is in.

Resightings were almost all made from locations across Bird Island, with the exception of one resighting from King Edward Point, South Georgia, and one from onboard from the Fishery Patrol Vessel Pharos.

Data quality:

Field_sex and field_age were determined by field observations and so may be inaccurate.

Where morphometric data are missing, this is due to the bird having been released immediately after ringing to avoid stress.