Pondering the plight of the planet’s penguins is not a happy exercise, but scientists are working on predicting how various penguin species will respond to emerging environmental threats. Two studies published today in PLoS ONE consider the dangers posed by extreme events – mega-icebergs and increasing summertime rainstorms – to Adélie and Magellanic penguins, two of the 17 penguin species on Earth.

Numerous climate models suggest that extreme events will increase in frequency (and shift locations) as the world warms. In coastal Argentina, this could include an uptick in summertime rainstorms that drench otherwise arid areas – areas like Punta Tombo, where Magellanic penguins come to breed between September and February. Problem is, young Magellanic penguin chicks are vulnerable to these drenchings, especially between the ages of 9 and 23 days old. That’s when the chicks are both too big for their parents to protect and are covered in soft down rather than waterproof feathers.

Anyone who has been caught in the rain in a down jacket knows the feathers lose their power to insulate when they get wet. So, rainstorms are a particular threat to the chicks, which are likely to freeze and die if they can't dry off.

Over 27 years, between 1983 and 2010, a team from the University of Washington and the Wildlife Conservation Society studied the multitude of factors responsible for chick mortality in the Magellanic breeding colony. Overall, starvation was the mostly likely cause of chick death. But in some years, these summer storms – especially the anomalously long or intense ones – were responsible for the majority of chick deaths, killing as many as half the chicks in the colony. Stronger storms killed more chicks, including older ones with proper feathers. Nests flooded, preventing the baby birds from escaping. The situation is compounded by a shift in the penguins’ arrival time at Punta Tombo, the team observed. Recently, the birds have been arriving and breeding later in the year – in October – presumably due to prey fish arriving later. This means that more chicks will still be downy and vulnerable come November and December, when the storms pick up.

An Adelie penguin walks over an automated weigh bridge at Cape Crozier. The bridge identifies each penguin and measures how much food the penguin brings back from foraging trips. Image: David Gremillet

The news isn’t all bad, though. In Antarctica’s Ross Sea, another team studying Adélie penguins over a 13-year period found that the birds can mostly adapt their foraging behavior to varying amounts of seasonal sea ice coverage. That’s good because scientists predict that sea ice coverage will shift dramatically in coming decades, with summer coverage shrinking as oceans warm. Adélie penguins have a complex relationship with the sea ice. It hosts prey species (like krill) on its underside and is essential for finding food, provides a site for the penguins to rest and molt, and eases migration. But too much, or too thickly packed sea ice close to shore, especially during chick-rearing, can be a bad thing: Penguin parents have to travel farther to the ice’s edge to find food, and longer, costlier journeys mean that chicks often end up being fed less.

But data gathered over those 13 years suggest the species displays enough behavioral plasticity to cope with a wide range of sea ice coverage near their breeding grounds, modifying their foraging trip length and frequency appropriately.

What they can’t deal with very effectively is a combination of shifting sea ice and mega-icebergs, which until recently happened infrequently enough to be considered an extreme event. From 2001 to 2005, during the time the team was studying the penguins, two enormous icebergs – each measuring tens of miles on a side – collided with the Ross ice shelf near the penguins’ breeding grounds at Cape Crozier, Ross Island. The bergs blocked the normal flow and formation of sea ice and messed with the ocean’s primary production of food. Unable to adjust their behavior to cope with these mega-bergs, the penguins and their chicks suffered (though perhaps not as much as Emperor penguins, who lost half their breeding adults). So, it seems that the birds' ability to deal with variations in sea ice coverage has a limit, and giant blocks of ice are a real problem. That’s not good because guess what happens when the globe and its oceans warm? More mega-icebergs.

Citations:

Lescroël A, Ballard G, Grémillet D, Authier M, Ainley DG (2014) Antarctic Climate Change: Extreme Events Disrupt Plastic Phenotypic Response in Adélie Penguins. PLoS ONE 9(1): e85291. doi:10.1371/journal.pone.0085291

Boersma PD, Rebstock GA (2014) Climate Change Increases Reproductive Failure in Magellanic Penguins. PLoS ONE doi:10.1371/journal.pone.0085602