Methodology:

Observational data is collected as part of a long term population monitoring initiative carried out over multiple decades. The data is gathered following standard ground survey methods at the two South Georgia shag colony areas present on Signy Island: North Point and Shagnasty Island. South Georgia shag pair numbers and chick numbers are recorded at North Point, and pair numbers are recorded at Shagnasty Island. Data has been collected by a number of different observers, who are listed with the count data.

A minimum of two experienced observers survey each colony area at least twice on the same day. Surveys are repeated until the two count totals are within 10%. The mean count value is then calculated and presented. To count pair numbers, nests at which an adult appeared to be incubating (occupied nests) are counted. Nests are observed either peripherally (from edge areas of each colony), or from a nearby vantage point (30-50 m away, using binoculars).

At North Point, past counts varied where sometimes the number of adult birds were counted, and sometimes total number of nests. In earlier counts, the date of the count is not always known, and earlier counts were typically done earlier in the season than is standard now. Since 1997/98, all counts have been of nests. Since 1988/89, all nest counts were undertaken between 23rd November and 19th January.

Chick counts are also undertaken at the North Point colony. Some earlier chick counts report the number of chicks that were ringed and is therefore a minimum number of chicks, as the original report does not state whether all chicks were ringed. Notes with the data indicate what was counted, where it was possible to ascertain this information from the original report. Chick count dates vary year-on-year, and some may be a count of eggs that have hatched and others the chicks that have survived almost to fledging. Since 1996/97, chick counts have taken place between 6th January and 6th February to count chick survival to fledging, which occurs January - February each year. No chick counts have been undertaken at the Shagnasty colony, due to difficulties in accessing the colony.

This data has been collected by British Antarctic Survey (BAS) researchers as part of an on-going BAS long-term population monitoring programme to determine population size and breeding success trajectories.

Data quality:

Differences in the methods are specified under Comments in the data.