Methodology:

Gentoo penguin colonies, predetermined as distinct groups of breeding pairs, were selected and surveyed using ground counts starting in the 1978-1979 season. In total, ten Gentoo colonies were surveyed annually, and in this dataset those colonies are combined for total counts per season. Optimal count dates were determined by observed phenology each season.

Monitoring comprised of counts of occupied nests and incubating nests for gentoo penguins. Nests were categorised as "incubating" (at least one egg present) and "occupied" (no eggs observed) either through manual nest marking, or observations from the colony edge using a tally counter. This was carried out one week after peak egg-laying (CEMP Standard Method A3A). Subsequently, fledgling counts were completed when all chicks had entered creche (CEMP Standard Method A6C). Counts were always individually repeated three times on the same day, until within 10 percent of each other. From the 2006/2007 season onwards, hand-held GPS devices were also used to provide specific coordinates of each surveyed colony.

An annual index of breeding population size was then calculated by determining the means of the number of occupied nests and incubating nests for several aggregated colonies. Breeding success was calculated by taking the annual number of creched chicks prior to fledging, divided by the total number of breeding pairs

Data quality:

Standard CCAMLR (CEMP) monitoring methods were implemented in 1996. Prior to this date, counting methods and timing of counts may have varied, which should be considered when comparing counts and calculating inter-annual trends from previous seasons.

For some seasons, only information on specific parameters was possible to obtain (when the base would open late/shut early). In some years, certain data pertaining to chick counts was not possible to obtain. For NA values in the column titled 'Total number of nests without eggs", which is carried out mid-season, some, if not all failed nests are abandoned by the time of the survey. Their stones are then stolen by other nesting birds, and the nests are no longer visible to field assistants. Abnormalities or the lack of data collected for other reasons is explained in the comments alongside that season's data.

More details on the counts can be provided upon request to the Polar Data Centre.

For this publication on annual gentoo penguin population monitoring, individual colony counts across the island were combined into totals per season. For additional details as to colony counts within Signy Island, please contact the Polar Data Centre.