Investigations into climate influence on population dynamics of yellow-eyed penguins Megadyptes antipodes

Abstract

Since 1980, the yellow-eyed penguin Megadyptes antipodes has had three seasons of poor breeding success or low adult survival. Causes for poor seasons are not identified but could be related to climate - in particular, the El Niño-Southern Oscillation event, which affects ocean currents and climate over the penguins' range. We carried out an exploratory analysis to determine whether fluctuations in penguin population variables were correlated with fluctuations in climate variables. Population variables across breeding areas showed consistently strong correlations with rainfall and sea surface temperature. We modelled changes in climate variables and penguin population variables to test whether the effect could be explained as a chance correlation. Investigations using these models indicated that the observed relationship was unlikely to have been due to chance. The models also suggested that fledgeling success increased in seasons that were slightly cooler and wetter than average. Modelling studies were also carried out on a historical dataset of penguin population variables in the 1930s. It was found that the population tended to increase in seasons that were warmer and drier than average. Average temperatures have risen and average precipitation levels have become highly variable in the study area during this time. Therefore, long term climate change in general, rather than the El Niño-Southern Oscillation events in particular, could be among the underlying causes of gradual decline in yellow-eyed penguin numbers.