What Is Going On With Adelie Penguin Populations?

Scientists have determined that Adelie penguin populations in the Ross Sea have shifted dramatically over the last decade.  While some colonies are in decline, others are growing rapidly, underscoring an earlier finding that many penguins do not return to the same nest sites annually.  Scientists have identified a range of factors that may contribute to the rise and fall of populations at specific colony sites.

The study by scientists at H.T. Harvey Associates, the Point Reyes Bird Observatory, and Oregon State University highlights the interactive effects that human and natural processes have on the abundance and distribution of an iconic species.  It also suggests that local processes (ice conditions, fishing pressure) and global ones--namely climate change--must be observed to understand what is causing population shifts.

Human and natural processes operating at a range of scales may impact the population dynamics of this remote species. The relatively stable temperatures in East Antarctica, the creation of large icebergs through calving, and human fishing (which cuts into the food stock for penguins) may all contribute to changing demographic patterns.

In the last decade, a large iceberg blocked foraging pathways for the Adelies, and many colonies experienced precipitous declines when they could not get to food. However, with the disintegration of the iceberg, foraging habitats became available and penguin reproduction increased.  Models of climate and stratospheric ozone suggest that temperatures in East Antarctica will be somewhat stable over the next decade, thus maintaining optimal conditions for the growth and colony expansion of the ice-dependent Adelie.  The recovery of colonies may also be related to humans' fishing of an important competitor with the Adelie--the Antarctic toothfish.  With prey more available, Adelie penguins can produce more offspring and expand colony size.