One of the aspects of migration that continues to fascinate people, is the ability of individuals to return to the same spot (either a wintering or breeding site), year after year. Such site-faithful individuals can be relatively easy to record, but recording site INfidelity has always been a major difficulty: if a bird doesn’t turn up where it was last year, you didn’t detect it, or it either moved or died. Tracking studies do not suffer from these problems, and now that tracking studies are producing data from individuals over multiple years, we can finally study the degree of consistency in routes and site selection over the entire annual cycle.
Recently, we published a paper reporting on this subject in Long-tailed Skuas. The paper is published in a theme section on ‘individual variation in migration and foraging in seabirds’ of the journal Marine Ecology Progress Series and can be accessed here. Don’t forget to click on the supplement, which contains a nice animation of the tracks!
Over half of the geolocator data used for this study was obtained from the Long-tailed Skuas in Ammarnäs, with the other part coming from colleagues working in Greenland and Svalbard. Together, we mapped nearly a hundred annual migrations of 38 individual Long-tailed Skuas. Several individuals were tracked over four or five years.
The emerging pattern is remarkable. While Long-tailed Skuas are generally faithful to their route from the previous year, they occasionally choose to go somewhere completely different. The highest consistency is found in early winter, around the time when they arrive at the main wintering area. After mid-winter, individuals start to deviate from their previous route. Such deviations can be huge: one individual went to the Benguela Current in four years, but after arriving in the second and fourth year, it simply flew 5200 km across the Atlantic to spend the remainder of the winter in the Falkland Current, near Argentina! In both occasions it used virtually the same route to get there and ended up in the same area. These patterns suggest they first check out local conditions before deciding where to go subsequently: either continue on their usual route, or on some alternative.
We also showed that individuals can show both ends of the spectrum: individuals showing ‘flexibility’ (deviations from their previous route), are not necessarily always flexible, they can also follow the same route twice.
The season is coming to an end. At least for us staying in the area. There are still skuas with chicks, although not many. In total we recaptured 19 loggered Arctic Skuas and retreived their migration information over the last year. We gave all these birds new loggers and caught an additional 7 birds that also got loggers. Quite unexpectedly we got yet another logger back. The other day we met a British couple that were staying in the area already for a week. They were making a film on the nesting and hatching of a red-throated diver nest. They found one of our loggers with a bit of the blue ring attached. They picked it up but later put it down on a tussock, because they thought we put it there intentionally for some kind of measurements.
Then they ran into Barbara Ganter and Hans-Ulrich Rosner, our fellow researchers working on Dunlin in the area, who told them that we would be extremely interested in getting the logger back!When we met the couple they had just spent 2 hours searching for ‘the precious’, but could not find it back. Together we searched for another hour systematically and checked every tussock in an area the size of a quarter football field. Just at the point when we were about to give up, one of them found it back!! The couple was so relieved! And they were the heroes of our day of course! That brings our total to 20! Last year we ringed 53 birds. It is clear that a large part of those either did not return, did not breed, or whose eggs hatched before we had a chance to catch them. One of the things we will dive into in the analyses if the El Nino may have had any effect on the early breeding season for some pairs or the lack of breeding for other pairs.
We are also seeing back the first birds that were ringed as chicks in 2014. That was a very good breeding year resulting in some 100 chicks ringed of which a large proportion also colour ringed. They do not breed yet, but hang around and sometimes seem to team up with a breeding pair.
In contrast to other areas in Europe we had extremely good and warm weather. Yesterday it was even 27 degrees! The caretaker of the lighthouse told us that no one in the nearby village Gamvik could remember that such temperatures were ever recorded before! Even swimming in the Barents Sea is not an achievement anymore.
On last Sunday Hans gave a presentation at the lighthouse for locals of Gamvik and tourists. It was well visited and it was striking to notice that people do not seem to be aware that they are in a very special place, home to the largest colony of Arctic Skuas! We are leaving Slettnes now and will return next year to meet up with our world travellers once more.
After only three weeks of fieldwork, we are leaving Ammarnäs today already. With no breeding skuas and lower-than-usual abundance of some waders, including Red-necked Phalaropes, it was a rather short and ‘slow’ field season. Even so, we have been successful in deploying 14 new geolocators on phalaropes, and, more importantly, we managed to recapture four of them; two males and two females. I will dedicate the coming period to the analysis of these tracks in comparison with those obtained at other sites between Greenland and Tobseda (or Yamal, if Jasper has been successful!).
Catching the last five phalaropes has been a rather wet experience. For some reason, the few small flocks of phalarope females choose to occupy the least accessible ponds: those with extensive buoyant vegetation mats. Its easy to sink deep into this… We are using adjusted rubber boots to enter these ponds, with holes in it to let the water out. And we take off our pants to keep them dry… But in several cases this was not enough: we were sinking waist-deep into the mud and vegetation. The last phalarope to be captured took some extra effort. Christian eventually swam to it in order to flush it into the mistnet, successfully!
During the last few days, we ringed some chicks of Red-necked Phalaropes, Ruff, Redshank and Common Sandpiper. Another highlight for all of us was a recently hatched Common Cuckoo chick in a Meadow Pipit nest. The little monster had already showed the door to the Meadow Pipit chicks, which lay dead outside the entrance.
You wouldn’t think we are at 71°N, with today’s temperature: 22°C, warmer even than in Rome and hardly any wind. This means mosquito bonanza!
Nearly all Arctic Skuas have hatched by now, but we have seen no chicks older than 1 or 2 days and several nests with dead chicks. The feeling that the food situation is bleak this year settles in more and more. Arctic Terns are not breeding either and one skua threw up a vole. The outskirts of the colony are either vacant or birds hang around but have not produced eggs.
The only breeding pair of Great Skuas lost their chicks within a few days, another sign that even they cannot feed their chicks. The logger information shows that the breeding Arctic skuas go out to sea sometimes for more than a full day leaving their partner at the nest.
In the meantime we managed to recapture 19 individuals from last year. It was a struggle against time, since many nests hatched so early. Catching them on a nest with a chick does not seem to work at all. Apparently the chicks need less brooding than e.g. waders and if we take the chick away they won’t return to the nest to sit on the egg left. Also we found out there are at least 50 ways why the catching fails, despite the fact that the snare system works well in principle. Either the battery power is too low, the bird simply escapes, the distance is too far for the remote control, the bird won’t sit down or in the worst case, the coil of the snare is broken.
The loggered birds showed the same variation as last year, wintering in south-America, South Africa, the Caribean, West Africa and one even off the coast of Spain. Of the four couples we recaptured the partners each went their own way, so they probably meet each other only here on the breeding grounds again.
On the Red-necked Phalarope front we also had some successes: 4 recaptured birds. One loggered bird lost its logger and one lost its nest, making catching impossible. Three of them went to the Arabian Sea, one even as far south as Mozambique. Of two of the birds we had tracks from last year. The tracks in the consecutive years were nearly copies!
Today we had a foreign surprise up in Björkfjället… Johannes has been studying Dunlins around Ammarnäs since 2008. Since last year, we have been collaborating in a circumpolar project on nest predation/survival rates in sandpiper species, focussing on Dunlin. This year, this was extended with another circumpolar collaboration, which aims to map the migration route of all subspecies of Dunlin (there are quite a few, depending on your taxonomic taste).
This morning we went up to Björkfjället to deploy geolocators on three Dunlins. After I retrieved the third bird from the trap, I noticed it had a metal ring! In previous years, Johannes colour-ringed a number of adults, and metal-ringed many chicks in the preceding years. Hence, my first and only thought was ‘this must be a bird ringed as a chick by Johannes’. Little did I know… I handed the bird to Christian, who had a proper look at the ring. ‘PARIS’ it read!! Hence, this bird got his ring somewhere in France.
Dunlins colour-ringed at Ammarnäs have been resighted in, e.g., The Netherlands and Portugal, showing a south-western migration direction. In this respect, the connection with France is not very surprising. However, which stopovers individuals use for what period is not revealed by these colour-ring resightings, but will hopefully be uncovered next year… if we manage to recapture them!
Yesterday, we had great success with Red-necked Phalaropes. We recaptured two males that received a geolocator last year by Michiel, Piet and Tim. Both birds had a full year of data, showing nice tracks down to the Arabian Sea.
Finally some news from Ammarnäs. Up until today, we had quite a ‘slow’ season. Lemming abundance has plummeted in late-winter, and thus virtually all Long-tailed Skuas are skipping this breeding season (except some weirdos far south at Kraipe and Aigert). We observed some small or medium-sized flocks of skuas that will probably make it back to sea in the coming two weeks.
Hence, our main target has been to (re)capture Red-necked Phalaropes in phalarope-city, Gelmetje. However, this didn’t went smoothly in the last week; we did find some nests, but couldn’t find any birds carrying geolocators. Nor did we find the usual ‘female-flock’ at lake Gelmetje. Deploying all available loggers therefore seemed difficult. This all changed today. While some males have been incubating for about 10 days, we now encountered a decent number of females and found a new nest of a male with logger, containing very freshly laid eggs! We didn’t manage to catch this male (yet!), but we did recapture a female with a logger it got last year by Tim, Michiel and Piet. Great!
The big surprise came only when we returned to the research station: it is one of the two females of which we already had a track! Thereby, the two years of data from this individual sheds some first light on one of the questions brought up by the paper in Journal of Avian Biology on phalarope migration. In this paper, we show that Red-necked Phalaropes usually use several areas within and adjacent to the Arabian Sea, instead of staying at a single site during the entire winter. For example, an individual may arrive in the Gulf of Oman, stay there for some time, then fly south to the spend some time along the southern Omani coast, and subsequently travel to the Gulf of Aden. These movements are presumably in response to monsoon-driven changes in where and when food is available, and the question is to what extent these movements are similar between years. Are they direct responses to local circumstances, changing from year to year, or routes learned during early life, and repeated in subsequent years? This female stayed at three distinct sites during the 2014-15 winter, but spent the entire winter in the Gulf of Aden during 2015-16, thereby showing that individuals can change itineraries between winters.
After five days in the field we are more and more puzzled about this season. We had the first Arctic skua chick yesterday, which is extremely early, and many more nests are about to hatch. These birds must have started laying eggs mid May! Also the Fieldfare chicks nesting near the lighthouse are about to fledge and the vegetation is two weeks ahead. At the same time many skua territories of last years are not occupied and in many territories birds are just hanging around. We also still find nests that were just started. The Red Fox is present again and indeed we found two nests predated already.
Up to now we recaptured 7 Arctic Skuas and their loggers show the wide variety we are used from them: wintering in south America, South Africa and the Caribbean. The 4 out of 7 that we recaptured last year as well, took remarkably similar routes.
Today was rainy with 6/7 Beaufort, not really weather to catch skuas. Besides we had some troubles with our catching device, the snare. It is quite ingeniously constructed around a remotely controlled vacuum cleaner spring, but now it needed some special technical attention (and a new set of batteries as it turned out later). Nevertheless we went outside to check territories at the outskirts of the area and look for Red-necked Phalarope nests. Tomorrow is going to be sunny and the day after even 15 degrees! Time for a dive in the Barents Sea!