Saturday, March 7, 2009

Penguin Week - Adelie Penguin

The penguin week idea seems to have not only stretched out beyond the week, I am now into the second month of trying to get some Antarctic themed posts done. Here is the latest installment.

The Adelie Penguin (Pygoscelis adeliae), along with the Emperor Penguin is a true penguin of Antarctica. They only nest on Antarctic islands and along the continent where there is a 'just right" combination of ice and snow free breeding areas juxtaposed with areas of relatively consistent and nearby sea ice. Most of the year they are found living in the pack ice. They forage under the ice for krill feeding on the algea growing on the underside of the bits and pieces.

In early October they begin to return to their breeding colonies. In keeping with my one place-one penguin species concept I used in my previous penguin posts, I am going to talk about Adelies at Paulet Island, a fairly small island in the Weddell Sea just east of the Antarctic Peninsula. Here (PDF) is a good overview of this island with most of the information coming from Oceanites work. There is a great aerial photo of the island in this PDF that gives a good view of the extent of penguins breeding on this island. This is one of the landings where most visitors to Antarctica get to experience Adelie Penguins en masse. A number of these guidelines for other islands can be found here.

And what a mass of penguins it is. Paulet Island is home to about 60 to 100 thousand pairs (so the actual breeding population on the island is somewhere between 120 and 200 thousand individual birds). And those are figures from about 20 years ago and probably pretty wild guesses at that. I suspect that given the available space on the island and my perception of vacant colonies, it is probably still at least that many penguins if not more. It is very hard to estimate the number of birds without quite a bit of effort, but one of the things that Oceanites has been doing is trying to get good estimates of the number of breeding pairs at these large colonies by GPSing the colony boundaries for all the colonies on the island and then applying a density figure to at least get a better estimate than the good old ocular estimate, i.e. "we eyeballed it".

These are tough birds. They nest is very inhospitable conditions and seem to do quite well even when the weather is not very nice for penguin counters.

A rather small colony at Paulet.

This is a view of the main landing beach at Paulet from the top of a nearby bluff (also pretty well covered in breeding penguins). The dark mass in the middle is the remains of a rock hut built by Captain Larson and twenty men after their ship the Antarctic sank in heavy pack ice in February 1903. They spent the winter of 1903 on Paulet, eating penguin and seal. Larson and five of his men managed to get to (somewhat) nearby Snow Hill Island in November, where the Nordenskjöld expedition they were sent to rescue were located. You can read more about this expedition here.

Another view of some of the colonies on the beach at Paulet.

Adelies nest in rather dense, regularly spaced colonies.

A pair of Adelies at their nest on the Fish Islands. The bird on the right (which appears to be the female to my eyes because of the slighter build of the bill - but I am quite out of practice at determining the sex of a penguin so it is just an educated guess) has just returned from a feeding bout and is initiating a nest relief with her mate. Notice how clean she appears compared to the male on the nest. One of the most critical time periods in determining the fate of a nest early on in the season is the first nest relief when the female returns after a feeding bout she makes right after laying the eggs. If she is not back to relieve the male within 10 days (give or take a day) the male will abandon the nest so that he can feed too. By that point he has been fasting for about two months at the colony and has reached the end of his physiological rope.

Sometimes late snowfall can completely bury nesting penguins. It can impact the breeding success of some pairs when the incubating bird forms an ice bowl around it and the meltwater doesn't drain from the nest and kills the eggs. Although probably not as important as a driver in determining Adelie populations as the environmental conditions related to sea ice, the loss of a years breeding can contribute to population declines when it starts happening with greater frequency. Heavy snowfall during this time seems to be increasing in frequency as more of the ocean surrounding the Antarctic Peninsula remains free of ice, increasing the transfer of moisture to the air. As with most declines in animal populations, the cause is often not just one factor but a multitude of factors that influence survival of individuals and their ability to produce offspring.

Clicker in one hand and the other is used to mark my spot in the colony when I am counting.

We arrived at Paulet just as the chicks were hatching. Many of the nests still had eggs, but a good number also had small chicks about this size, probably about a week old.

We were also able to see a number of birds hatched the previous year on this trip, a sight many people to not get to experience. These birds are easy to tell from older birds by the lack of black on the chin. They attain that plumage after their first full molt when they are one year old. They rarely return to the breeding colonies at this age, but spend much of their time just trying to survive and attain the mass needed to attempt breeding. They are often found in areas of high krill concentrations where there is still sea ice. We found many of them south of the Antarctic Circle in Marguerite Bay where there was still a fair amount of sea ice.

This is a sign at the former British Antarctic base Faraday, now the Ukranian base Vernadsky.

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