Guillemots Go to the End of the Earth in Pursuit of Retreating Sea Ice
The annual announcement of the minimum extent of the Arctic’s summer sea ice has become one of the more important metrics by which we measure the rate of change of our warming world. This year’s minimum extent of 3.4 million square kilometers (1.32 million square miles) on September 16th broke the previous minimum set in 2007 and was half of the average minimum for 1979-2000. This 3.5 million square kilometer loss in ice extent in the last twelve years is equal to an area two times the size of the State of Alaska.
After my three months on Cooper Island each summer studying Black Guillemots and their response to the ice retreat, I am always surprised to return to find that the media is again discussing the ice loss primarily as a physical phenomenon, similar to what is being reported in the decrease of glaciers, rather than one of unprecedented biological loss and degradation of a unique marine ecosystem. The discussion of loss of tropical rainforest, another unique ecosystem undergoing major reduction, is almost always framed in an ecological context, with discussion of the effects of habitat loss on habitat and species. This contrasts with the media’s treatment of the loss of arctic sea ice where there may be token mention of some of the megafauna affected, such as walrus and polar bears, but a failure to mention that the less charismatic components of the ice-associated ecosystem, consisting of ice-algae, zooplankton, fish, seals and seabirds, now have far less habitat supporting them as they did in the last two decades of the Twentieth Century. The complete disappearance of the summer sea ice habitat in the Arctic, predicted to occur in this century, will be the largest loss of an ecosystem the planet has experienced in modern times.
The Black Guillemots breeding on Cooper Island are part of a guillemot subspecies that is one of the few seabird populations dependent on ice-associated prey throughout the year. Our forty years of observations at the Cooper Island Black Guillemot colony has shown how the rapid decrease of ice in the last decade has reduced breeding success, as parent birds provisioning young in August and September struggle to find prey in ice-free waters. In the past few months, we have found another way in which the reduction of sea ice habitat is affecting the birds. By deploying geolocators, which are attached to a bird’s tarsus and use time of sunrise and sunset to identify geographic position, on five breeding birds in 2011 we were able to track their movements from September 2011 to June 2012.
I frequently saw Black Guillemots at the ice edge in September and October during my early years in the Arctic when I was observing birds and mammals at the ice edge in the Chukchi and Beaufort seas. The unprecedented retreat of summer ice in the past decade has made me wonder where guillemots now go after breeding as the ice edge in fall is now hundreds of miles north of the Alaska coast when it used to be just offshore Figure 1 The data we retrieved from the geolocators this June shows that guillemots are still going to the edge of the sea ice in the post-breeding period, but now are having to traveling 300 to 500 miles north in search of their preferred sea ice habitat.
The extent of this post-breeding pursuit of sea ice is demonstrated in the movements of a male guillemot that has bred on Cooper Island for the past decade Figure 2. After its young had fledged on September 4, the bird flew north to the shelf break and remained there for a little over a week before starting a one-week 300 mile trip to the pack ice edge. Our discovery that post-breeding Black Guillemots now make a 600 to 1000-mile roundtrip to the fall ice edge, when in the past they encountered ice just north of the Alaskan arctic coast, has a number of implications. It demonstrates that the guillemots breeding on Cooper Island now have the increased energy demands of extensive post-breeding movements at a time when they have just completed their three-month breeding season and while they have the increased energy demands of replacing their feathers – limiting temporarily their ability to fly. The findings also suggest that guillemots will continue to move north in search of ice after breeding. As summer sea ice is predicted to decrease and eventually disappear in the Arctic over the next few decades, guillemots in northern Alaska guillemots will have increasingly long post-breeding movements that will eventually culminate in their moving north in search of ice in an Arctic Ocean that has no ice.
Our research on the movements of guillemots is continuing as we outfitted ten birds with geolocators near the end of the 2012 season. Their post-breeding movements this year will be of great interest given the record ice retreat of this past fall. Additionally, Iain Stenhouse, who supplied Friends of Cooper Island with the geolocators in 2011, and I will be working more with the 2011-2012 data logs to examine the effect of ice on movements to and from the Bering Sea wintering grounds.