100 nests in designated Adelie and Chinstrap penguin colonies are marked and then regularly monitored. Data are collected on when eggs are laid in each nest, when they hatch, when eggs or chicks are lost, and when chicks become unguarded. Data exist from 1996 onwards. For Adelie penguins, 100 nests in a colony designated A41 was monitored between 1996 and 2002, from 2003 onwards 100 nests in a colony designated A39 were monitored. For Chinstrap penguins, 100 nests in a colony designated A69 were monitored between 1996 and 2015, from 2016 onwards, 100 nests in a colony designated C66 were monitored. No data were collected in the 1997-98, 1999-2000 and 2010-2011 seasons. To calculate the annual hatching date a binomial model was fitted using the proportion of nests containing one or more chicks as the response variable and the date in days after 1 Oct as the explanatory variable. This model was fitted for each species and year separately. The dose.p function in the MASS package in R was used to derive the day when 50% of nests contained one or more chicks to produce the mean hatching date for each species-year combination. Mean laying dates were back-calculated from the mean hatching dates by subtracting the average incubation periods for each species (35 days for Adelies and 36.4 days for chinstraps, which are relatively constant between years). This has been calculated for data from 1996 to 2016.

Adelie and Chinstrap penguins were fitted with both GPS loggers and time-depth recorder (TDR) tags for between two and fourteen days in order to log their three-dimensional foraging trips. Tags were deployed between December and February of 2011/12, 2013/14 and 2015/16 with a total of 36 Adelie penguin GPS tracks, 37 Adelie penguinTDR tracks, 52 Chinstrap penguin GPS tracks and 48 Chinstrap penguin TDR tracks.