Methodology:

Observational data is collected as part of a long term population monitoring initiative carried out over multiple decades. Counts take place over a number of days, at up to 21 colonies across Bird Island. Not all colonies are occupied in all seasons.

Annually collected egg-laying data from two colonies on Bird Island (Wanderer Ridge Extension and Pearson Point) are used to determine optimal survey dates for breeding pairs, at which time all other colonies are surveyed and occupied nests recorded.

Birds are observed either from within the colony, or from a nearby vantage point using binoculars. Birds are counted if they are sitting tight, or are deemed to have well-built nests. Experienced observers survey each colony area at least twice in the same day. Surveys are repeated until the two counts are within 10%. The mean count value is then calculated and presented. More recently, some counts have been conducted using counts of nests in photographs.

The 1989/90 and 1994/95 data were collected by Centre for Ecology and Hydrology researchers (Sarah Wanless and Mike Harris). Subsequent data has been collected as part of the British Antarctic Survey long-term monitoring programme at Bird Island. Data has been collected by a number of different observers, who are listed with the count data.

All data were collected under permit from the Government of South Georgia and the South Sandwich Islands.

All sampling procedures used were regulated by the British Antarctic Survey Ethical Review Committee in collaboration with Cambridge University and the UK Home Office.

Data quality:

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