Penguin reproductive season crash in the Antarctic
Male Adelie penguin feeding chick while female partner rests before departure.
I have been back for some weeks now from my campaign at the French Antarctic research station at Dumont D’Urville (DDU) at Terre Adelie. While pursuing my scientific programme at the station, I was also writing regular reports for school kids in Monaco who were following my mission. As an example of the posts I sent, but also to inform everyone a bit about events in the field, you will find an updated copy of one of my final posts I wrote for the kids.
This year was a disaster for Antarctic penguin populations in the Terre Adelie region of the Antarctic.
The official end of the emperor penguin breeding season typically comes by mid-December, when the last of the season’s emperor chicks finish fledging and depart the colony grounds for sea. This year, few chicks survived to fledging and the departure of the chicks happened up to 6 weeks late, with most chicks departing at the end without having finished their moult. Most of those likely died before reaching the open ocean. Though it was not a complete loss, some chicks managed to make it to sea, the reproductive year for this colony, the one at which the film “March of the Penguins” was filmed, was one of the worst since monitoring began in 1950.
The Adelie pairs each lay their 2 eggs in December, with hatching usually happening by the end of the month, and fledging occurring by the end of January. Average nesting success is usually between 0.8 (in very bad years) and 1.2 (in very good years) chicks per nest successfully reared to fledging. This year, from the ~60,000 nests we monitor around Terre Adelie, not a single chick survived to fledging. The first complete reproductive collapse ever seen in the territory.
All other avian species struggled, with record poor reproductive success for the southern giant petrels (Macronectes giganteus), cape petrels (Daption capense), Wilson’s storm petrels (Oceanites oceanicus), snow petrels (Pagodroma nivea), and south polar skuas (Stercorarius maccormicki).
The reasons for the bad year are related to a variety of proximate and ultimate causes, some of which are still poorly understood.
The proximate explanation:
There is more and more sea ice around the French Antarctic research base at DDU), and throughout much of the Southern Ocean, this year. This sea ice is much thicker and more vast than in previous years, especially in this region. More and more frequently over recent years, the Astrolabe, the French ice-breaker that supplies the Antarctic stations, gets trapped in the ice and has difficulty reaching the base. Supplies at DDU were critical this year, and there was a real threat of base closure for the first time since it was established in 1956, as the ice-breaker never managed to make it closer than 40 km to the base, the limit of comfort for supply transport by the small helicopters they use. More and more tourist boats, such as the Russian ship Akademik Shokalskiy that made so many headlines in December, are also getting trapped. In past years, on 1 January, personnel at DDU did a 'polar bear plunge' where they made a quick swim in the sea, and even during this first week of January, boats had to be used by researchers to reach the various offshore islands to monitor Adelie populations. This year, though there were cracks and puddles in the sea ice, we were able to walk to all of the colonies on the near-shore islands and capes throughout the entire Antarctic summer.
The hyperextensive sea is the primary proximate reason for the poor breeding year for the birds. The open sea never made it closer than 40 km to the base, so penguins had to travel 80 kilometers round-trip to forage. This is not a trivial distance for a flightless species to cover to forage for food. Walking that distance requires a huge effort. Fortunately, penguins can toboggan on their stomachs, traveling faster with less energetic effort.
However, during the relatively ‘warm’ summer season, snow no longer accumulates on top of the sea ice and daily thermal fluctuations create a freeze-thaw cycle on the ice surface that leave the sea ice hard, slippery, and covered with very sharp ridges. Thus, during the height of the summer, for a variable period each year and depending on the storm cycles that bring fresh snow, penguins are unable to toboggan during foraging trips. The larger emperor penguins, at ~45 kg for an adult, are able to carry sufficient body mass for considerable energy storage (fat), and can manage to handle the extra travel distance to feed their chicks, though with some difficulty: seen in the longer parental foraging trip durations, slower chick growth, increase in chick mortality, and delayed chick fledging. The much smaller Adelies, at ~8 kg for an adult, do not have the capacity to carry much extra energy storage, and the extra foraging distance is thus a much larger barrier for them. In a normal year, parental shifts during chick care average 1.5-2 days. Walking on their very short legs, or even tobogganing, to cover a distance of 80 kilometers is not possible in 2 days. It is therefore easy to see why we had nearly 65% chick mortality within a week of hatching, as chicks came to the end of their energy stores while waiting for a parent to return with food.
The sea ice around the Antarctic continent is never stable; it is constantly in motion as the tides raise and lower the sea level, the strong winds push the ice in different directions, and ocean currents move the ice from below. We walk on the sea ice every day for our work. Every day is different: a new environment. There are new cracks that must be navigated around or jumped over.
Some old cracks have disappeared as ice chunks have moved back together. Ponds of melted ice have shifted, or grown, or disappeared. Each day that we visit other island colonies of Adelies, or the emperor penguin colony on the sea ice, we have to find a new pathway. This necessity of dealing with the sea ice conditions on a day-to-day basis, means that everyone on the base is hyper-aware of the change in sea ice extent and general weather patterns in recent years.
There are different proximate reasons that explain why the sea ice is so much more extensive this year.
Ocean Currents: The Southern Ocean has currents that circulate the water in a clockwise (west to east) direction around the continent. This circulation of water pushes against the bottoms of icebergs and thin surface ice, moving the ice around and preventing it from forming a solid mass. These currents develop from many different intersecting influences, some of the most important include: the movement of the earth, the movement of the surface winds, the movement of warmer and colder pockets of water relative to each other (cold water is more dense and sinks; warm water is less dense and rises). With the increase in Global Climate Change effects, scientists are observing changes in many of the features that drive the currents. The changes are many and complex have led to a net weakening of the Southern Ocean currents. Hence, ice blocks are more stationary and can freeze in position more solidly.
Wind: The Southern Ocean also has air currents (wind) that also circulate in a clockwise (west to east) direction around the continent. The air currents are impacted by intersecting influences similar to those affecting the water currents: the movement of the earth, the movement of warmer and colder pockets of air relative to each other (cold air is more dense and sinks; warm air is less dense and rises), intersection with trade winds cutting across the Southern Ocean wind currents, intersection with winds channeled off of large icebergs, general topographic features, and land masses. Just as the ocean currents push around the ice from below, these wind currents push around the ice from above, similarly preventing it from standing still long enough to freeze very solid. When the Astrolabe, or other boats, get stuck in the ice, the wind is what usually helps it get free. When the wind blows strongly enough, or from a particular direction, the solid ice breaks into chunks as it spreads out into the vast expanse of the Southern Ocean, and the boats can find a new passage through the newly opened channels of open water. Among the many and complicated effects of Global Climate Change, there are many changes to the wind patterns. The changes themselves are many and complex and poorly understood, but they have led to an overall decrease in the large-scale wind currents, and sea ice and icebergs are not being pushed around as much.
Solar radiation: Solar radiation (sun energy) is also has a large effect on sea surface ice in this region. Light colored objects reflect a lot of incoming solar radiation, and dark objects absorb a lot of solar radiation, so different colored objects will warm at different rates, and to different temperatures, when exposed to sunlight. Scientists use a measure of solar radiation reflectance, called albedo, to study this characteristic. If you stand on top of the sea ice, or on the Antarctic continent and look around, you'll see everything is white, with a high reflectance of incoming solar radiation.
The open ocean is very dark, absorbing most of the incoming solar radiation. Just about any object you come across outdoors has a higher absorption of solar radiation than white ice/snow. Rocks, dirt, leaves, and lichens and moss all absorb a lot of solar radiation, warming faster than ice does in sunlight. But, a warm rock or patch of dirt sitting in snow causes the ice around it to melt, exposing yet more rocks and dirt, and you get a positive feedback driven ice-melting response. The more the ice melts, the more the remaining ice is exposed to warmth. Around DDU, when the sea ice is very solid, the ice reflects most of the incoming solar radiation, and stays cold and solid. But, when one or more little patches of ice melts and the sea or rocky islands become exposed, more warmth is absorbed and more sea ice melts.
Glaciers and Icebergs: Ice is constantly building up on the Antarctic continent and flowing down into the sea due to gravitational forces acting on the massive piles of ice. These glaciers extend out into the ocean all along the continental coast. Large pieces break off periodically and float out into the ocean as icebergs. These glacial extensions coming off of the continent and the icebergs can be massive, blocking sections of ice on the ocean surface or blocking/changing local wind and ocean currents. Global Climate Change is affecting large-scale changes to global and local climate patterns. In some areas of the Antarctic continent, there is now much higher precipitation (snow), while other areas have much less precipitation. In areas with higher precipitation, the glacial extensions grow faster (because there is more and heavier chunks of ice flowing down to the ocean) and more icebergs break off into the ocean. In areas of lower precipitation, the glacial extensions are growing more slowly, extend less far into the ocean, and produce fewer floating icebergs. The patterns are complex and very hard for us to predict and model because climate is a product of so many environmental factors. Around DDU, some of our problems with increased sea ice are the result of a large glacier called Mertz blocking part of the sea channel where the sea surface ice can be blown away.
This has been a problem since at least 2010, and nobody is sure how long it will continue. It could change with the next big storm, or the glacier could sit there for the next hundred years, forcing DDU to eventually switch to more reliable air transport, instead of the Astrolabe, for supplying our bases in this region.
While the sea ice is the proximate reason for the disaster that was the 2013/2014 reproductive season at Terre Adelie, and I’ve given you an overview of other proximate factors related to the extensive sea ice conditions, we still do not have the full story. In fact, the emperors do most of their chick rearing in late winter and through the polar spring, when the open sea is very far, so they should not have been so affected by the more extensive summer sea ice. Also, some of the king penguin breeding colonies in the sub-Antarctic are currently experiencing delayed and variable reproductive seasons, which has previously been identified as a sign of a poor foraging year. Since the richest foraging locations used by king and emperor and Adelie penguins all fall within the influence of the Antarctic Circumpolar Current, we are hypothesizing that there is poor resource availability in foraging grounds this year. Unfortunately, the remote locality of the Southern Ocean means that the ocean monitoring there is data poor, so it is very possible that the data we need to assess this do not exist.