25 May 2014

It's a bird eat bird world for South Georgia's macaroni penguins

Macaroni penguins walking across
the weighbridge to their colony.
Photo credit: BAS
SOUTH GEORGIA - More than 10 years of data have revealed new information about the survival rates of macaroni penguins on the South Atlantic island of South Georgia, helping scientists better understand the threats they are under.

A research team, led by scientists from the British Antarctic Survey (BAS), used the data collected from tiny electronic tags placed on the penguins' backs to explore year-to-year survival rates and uncover the biggest pressures on the population.

Their findings, published this week in the Journal of Animal Ecology, showed that one of the biggest threats the penguins face is predation by other seabirds.

The macaroni penguin population on South Georgia has declined by almost 70% since the early 1980s. To investigate this, adults and fledglings have been tagged with electronic transponder devices (much like those used by pet owners to mark their cats and dogs) since 2003.

An electronic scanner placed at the entrance to their colony then registered the tags and recorded each bird’s identification number as it came and went, over a period of ten consecutive breeding seasons.

Previous studies on penguin survival rates have focused on the influence of environmental pressures.

"Penguins are facing rapid changes in their environment, lead author Catharine Horswill, from BAS, said, "[B]ut at South Georgia ... we found compelling evidence that predators are the most important factor influencing the survival of chicks as they leave the colony for the first time."
Macaroni penguins emerging from
the sea at Bird Island, South Georgia.
Photo credit: Mick Mackey

The scientists found penguins were particularly vulnerable to predation by giant petrels, which also nest on the island. This was especially the case for chicks, with only a third surviving their first year.

Ms Horswill said, "This is a big leap forward as we had no idea that predation could be such a strong driving force."

"Knowing what drives survival rates of penguins puts us in a much better place to predict how these populations may change in the future.”

The study shows that macaroni penguins are influenced by both environmental and predation pressures. It highlights the need to study multiple causal effects across various stages of the life cycle in seabirds when looking at their survival rates.

Source
Electronic tags provide 10 years worth of penguin data [press release], 21 May 2014, British Antarctic Survey Press Office

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