Antarctic field work

By Alice Trevail.

Myself and Sebastien Descamps from the Norwegian Polar Institute have recently returned from seabird field work in Antarctica – definitely the most amazing place I’ve ever been. We were based at the Tor ornithological research station at Svarthamaren Mountain. Svarthamaren is located on a string of mountains, from which there is nothing other than snow and ice in both directions until you reach the Southern Ocean or the South Pole. The mountain range provides the vital rocky slope needed for birds to create nest sites. About 100km away from our field site is Troll station, which is the main Norwegian research base: a slow but relaxing six hour journey by snow-cat along the mountain range. Next stop from Troll is Cape Town, South Africa, via a 6 ½ hour flight over the Southern Ocean: Tor station certainly is remote!

We were at the colony for four busy weeks, home to three species of seabirds. Antarctic petrels (left picture, below) and snow petrels (centre) journey out to open water to feed on fish and krill, and south polar skuas (right) predate on both species of petrel.

The snow petrels are the most sensitive species to handling, so we only carry out some basic monitoring of the same set of nests each year. The proportion of active snow petrel nests in our study area (% of nests with a chick mid-February) was similar in 2016 as in previous years.

Antarctic petrels are our main study species. Not only do we count the whole colony but we also undertake more detailed nest monitoring, GPS tracking work and diet studies. Our main task was to deploy GPS loggers on the Antarctic petrels to study their foraging behaviour. They fly 200km to reach open water and then onwards to their foraging grounds in the poorly studied King Hakon VII Sea. They forage in an area of the Southern Ocean that is hugely inaccessible for humans, and therefore we know very little about what is going there (I’d never heard of the King Hakon VII Sea before either!). However, with constantly improving telemetry technology, we can combine GPS tracking studies with diet analysis and population counts of the petrels to learn about the Southern Ocean.

Stomach analyses can reveal differences in diet. These pictures show a mixture of krill and fish, left, and a bird feeding solely on fish, right. Oily krill is the more nutritional prey source, and so it was worrying that this year we found more stomachs full of fish.

The 2015-2016 breeding season for Antarctic petrels was the worst ever recorded since the first expedition there in 1985. The density of chicks in the colony end of January was only 0.07 chick.m-2, compared to ca. 0.8 chick.m-2 in 1985. This confirms the negative trend observed in the last few years (Descamps et al. Ecography in press). The GPS tracks showed a mix of foraging behaviours, with one exceptional bird paying a visit to the western Antarctic Peninsula, 2,600km away by straight line! Its early days in the project, this was the first of three years, but hopefully over the years to come we will be able to understand more about what is driving the decreases in the Antarctic petrel populations (left picture below). The colony was indeed quiet, the right picture below shows nests from previous years marked with yellow tags, all empty.

GPS tracks from all antarctic petrels:

We visited all of the skua nests in the colony for nest monitoring and contaminant analysis of the adults. The number of active skua nests in Jan/Feb 2016 was similar to previous years. The number of chicks at the end of the season has decreased since but inter-annual differences in “field work effort” (i.e. time spent to look for the chicks) may explain part of these differences.

One component of this project is to link the behaviour of the birds in the colony (e.g. aggressiveness, boldness) to their behaviour at sea (GPS tracking), their diet (stable isotopic ratios) and their breeding performance. To do so, we performed preliminary personality trials on 25 birds in Jan-Feb 2016. We filmed the behaviour of petrels exposed to an unknown object (a yellow plastic fish). These preliminary results will soon be analysed in order to set up a more specific protocol (based on a larger sample of birds) for the 2016/17 season and form part of a new PhD project here at SEGUL.

As part of a collaboration with Seb’s colleagues in Norway, we sampled feathers and blood from 20 adult skuas and 20 adult Antarctic petrels to investigate contaminants in the Antarctic food web. I also collected carcasses of Antarctic petrels, skuas and snow petrels (mainly chicks and failed fledglings from previous years) for analysis of plastic pollution.

I think this mostly summarises what was a busy four weeks in a fantastic seabird colony. I’ve left with huge admiration for the birds, and a lot of respect for this remote place. More about that here. I would like to say a huge thank you to the team at Troll station for everything they did for us – I wish I was still there!

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