Cape Crozier, January 2007. When you first set foot in the enormous Adélie Penguin colony here at Cape Crozier (Ross Island, Antarctica), you are inundated by a rush of noise and of smell, of life and of death. If you haven't seen penguins before, you will probably first focus on the life. Even among penguins, Adélies are especially entertaining-very busy, often mischievous (stealing neighbors' rocks for their own nests), and quite boisterous-constantly defending their space by bill-gaping, ecstatically vocalizing, flipper-bashing, and chewing on one another.
But there's also something hypnotic about seeing so many of them together, with their formal color scheme (one of nature's most reliable for an ocean predator: black above and white below) completely appropriate in the austere landscape of rock, ice, and windswept ocean. Scanning the few hundred thousand of them that I see every day between November 15th and January 25th (the austral summer), I'm often entranced by the homogeneity--countless little black-and-white, bipedal beings; nothing human in view, for scale. This seems an ancient and unchanging scene, innocent of the anthropogenic perturbations so characteristic of the rest of the world.
Eventually, despite all the Adélies' life energy, your attention is drawn to the dead--to the thousands of carcasses that litter the ten square kilometers of the colony. They are everywhere, most of them dried and yellow--carcasses partially buried in stones or guano, small remains, many with penguins nesting on top of them. On my first visit here, in 1996, I asked David Ainley (former PRBO scientist and 38-year veteran leader of Antarctic expeditions) why there were so many dead penguins around--strikingly more than I had seen in other seabird colonies around the world. He explained that, at high latitudes, the extreme cold temperatures keep the processes of decay at near standstill. So, after thousands of years of occupation, a penguin colony at 77˚ S accumulates quite a pile of dead bodies.
But why hadn't skuas scavenged all the dead chicks? Cape Crozier is also home to the world's largest population of South Polar Skuas, which make short work of any penguin chicks that die or wander from their home territory even briefly.
My original questions persisted over the subsequent 11 austral breeding seasons that I've spent working mostly with the living--resighting individual penguins banded as chicks, attaching satellite transmitters to some that we track on their foraging journeys, making diet observations, and measuring chicks. We are investigating the processes that determine why penguin colonies exist where they do, why some grow very large, why some disappear, why some fluctuate wildly, and how they respond to climate change.
Some of the answers were found right under our feet, in the dead penguins themselves. With colleagues from New Zealand and Italy we have documented the rate of micro-evolution in the DNA of penguins, comparing 10,000-year-old DNA in tissue samples preserved in this environment to that from current populations occupying the same sites.
After a few years, having gained a bit more experience with high-latitude Adélie colonies, I asked David why so many of the dead, at Cape Crozier in particular, were about the same age. A high percentage are crèched chicks (out of the nest but still dependent on their parents for food), about three weeks old, that appear to have died in a single season rather than representing accumulated mortality of centuries. He speculated that perhaps a giant iceberg had broken off of the adjacent Ross Ice Shelf when most of the parents were out foraging, blocking access to and from the colonies, with subsequent mass starvation of the chicks. Another explanation was offered by Steve Emslie (former PRBO Farallon biologist, now a paleo-ornithologist and professor at University of North Carolina), who visited our study site during the 2000-2001 season to ascertain the dates of the original occupation of the Cape Crozier colony. He was also astonished by the numbers of bodies. He guessed they were between 100 and 200 years old, affirmed that most of them appeared to have come from a single event, and suggested that perhaps a giant snow storm one year had buried all the chicks alive.
I have to admit that neither explanation seemed very convincing to me at the time, given that I had never seen either a giant iceberg or a giant snow storm (Antarctica is by far the driest continent on Earth), and that the scene I'd been observing then for several years seemed so permanent.
|An extraordinary snow storm this winter convinced Grant Ballard, pictured above with Adélie Penguins, that extreme events related to climate events could explain the presence of so many "sub-fossil" remains of same-aged chicks in the colony. PHOTOS BY VIOLA TONIOLO|
Events since then have shown that both hypothetical explanations are plausible. We have seen giant icebergs break off the Ross Ice Shelf (most notably in 2001--at 160 kilometers long, 'B15' was the biggest ever observed by humans) and crash into Cape Crozier, blocking almost all access to not just one colony but four of them simultaneously (at Cape Royds, Cape Bird, Beaufort Island, and Cape Crozier). This resulted in the deaths of many thousands of adults and chicks. We have also seen, especially in December 2001 and January 2005, the biggest snowfalls anyone can remember and some of the highest winds, depositing up to three meters of densely packed snow over scores of subcolonies in a single day, burying thousands of nests, adults, eggs (2001), and chicks (2005)--and skuas, too. Even today, many of those dead birds have yet to emerge. With all due respect to the dead, I feel amazingly lucky to have observed such spectacles first-hand. The odds are indescribably long of witnessing events never before seen by scientists (or anyone else) and thought to have happened only once in the past thousand years.
The resilience of the penguins to such rapid and drastic environmental change is awesome. After the big blizzards, most of the parents were able to eat their way out of the snow that buried them, and they learned how to navigate tiny passageways that remained around the giant iceberg, so they could get back to the open ocean and food. Adults subsequently moved between colonies at unprecedented rates to find ice-free nesting habitat and to improve their access to food. In the course of a single year, Adélies abandoned locations that had been occupied for centuries.
Now that the giant icebergs have gone north, knocked out of their positions by waves from a particularly violent storm in the North Pacific a few months ago, the penguins are having a great breeding season. It's almost as though the hard years served as training for their next opportunity, which they seized by breeding a week earlier than usual and raising very large chicks. Though several thousand more adults than usual were killed by storms and icebergs between 2001 and 2005, the breeding population is as large as it has ever been in the 30-plus years for which there are data. Apparently the penguins can cope--so far.
|Life goes on. Large Adélie chicks await their next feeding. VIOLA TONIOLO|
High winds and heavy snow lately have provided our research team with an unusual amount of hut-time (this is the sixth day out of the last eight that we have spent mostly indoors). I'm taking advantage of the time to catch up on data synthesis, do some writing, and wonder about the future. The penguins will keep trying as hard as they can--that's the nature of Adélies, and they are remarkably flexible. There is bound to be a lot of new nesting habitat available to them on a warming Earth--at least for several decades to come--since there are still hundreds of kilometers of future coastline to emerge from under Antarctica's ice-sheets. What's less certain is whether the ocean will continue to provide the apparently endless quantities of fish and krill that these birds rely on--especially now that industrial fishing ships are tempted into the Ross Sea's pristine waters by the collapse of the world's remaining fisheries.
Antarctica may seem huge to a penguin or an awestruck biologist, but the planet, in many respects, is rapidly becoming smaller.