This years’ field season has ended! Geert and Ingrid left Slettnes and Morrison and Rob left Ammarnäs on 2 July. Despite the poor breeding season for both skua species, some valuable data and observations have been collected. In total, 14 geolocators have been retrieved from Arctic Skuas, some with 1.5 years of data on some of them. The Long-tailed Skuas of Ammarnäs will have to wait another year before they can hand in their geolocators.
As I wrote in the previous blogpost, we have recaptured several Red-necked Phalaropes with loggers: 4 in Slettnes (1 female) and 4 in Ammarnäs (all females). One was deployed in 2014 and another in 2015 and they should have more than one year data. The high number of females is exciting (see my previous post).
Unfortunately, we have been unable to recapture any of the eight geolocators deployed last year on Dunlins, although we resighted three of them early in the season. High predation pressure, shown by both an artificial nest experiment (using quail eggs in fake nests to measure predation rate) and monitoring of Dunlin nests, is the likely explanation of this failure. Hopefully they return next year again!
On our last day in Ammarnäs, we went up to Björkfjället to finish the artificial nest experiment. We also wanted to see the Shorelarks, a species that has declined tremendously in the Swedish mountains. We were also hoping to catch a glimpse of the Wolverine that Martin saw a few days earlier. After a failed attempt to see this mysterious species, one of the large European mammalian predators, we didn’t really expect to find it. Then, at a distance of ca. 3km, I noted a Wolverine running downhill to a Reindeer carcass (with a White-tailed Eagle feeding on it)! We couldn’t believe our eyes! See the blurry video at long range below, where it is carrying a bone uphill. I couldn’t have dreamed up a better way to end the field season!
In both Slettnes and Ammarnäs we have been successful in recapturing Red-necked Phalaropes carrying geolocators, including several females. Interestingly, one of these females from Ammarnäs carried a logger that Tim and I gave her in 2014. She has managed to escape our catching attempts for several years!
In previous years, we had more recaptures of males than females, which has everything to do with their breeding system: females ‘only’ lay eggs and leave the incubation and rearing of the chicks to the males. Males can thus be captured on the nest, which makes it easy to target a specific individual and allows several catching attempts, while females can only be captured by mist net. The increasing number of females in our sample allows us to have a first look at hypotheses pertaining to the earlier arrival at the breeding grounds of females compared to males, something we already hinted at in our JAB paper. Do they: 1) start spring migration earlier, 2) migrate faster or 3) winter closer to the breeding grounds than males? We haven’t analyzed the new females yet, but the tracks of our first three females (captured in previous years) confirm that females arrive – on average – five days earlier than males. They showed similar stopover and wintering areas as males, excluding option 3 (closer wintering grounds). Option 1 and 2 require more detailed analyses, but large overlap between the sexes in the timing of departure from the wintering area, suggest option 2 (faster migration) rather than 1 (early departure).
But how to (re)capture phalaropes? Ingrid compiled the video below, which Janne proudly presented at school!
Normally, the Red-necked Phalaropes in Gelmetje start egg laying between 10-15 June, with some nest appearing a little later. This year, it took a long time before we found the first nest: an incomplete clutch on 21 June. Many pairs were still hanging around in pairs, apparently still in the process of finding a suitable nest location or still laying eggs. This give us the opportunity to capture several pairs, thus with females that yet have to start laying. These females were all surprisingly heavy: mostly between 40 and 45g. Until now, we only recorded such weights at the end of their stay, around 10 July.
We have managed to recapture two phalaropes with geolocators: both females! Surprisingly, one of these carried a logger that Tim and I gave her back in 2014. Amazing! The battery was empty, so we will have to return the logger to the manufacturer to get the data. Can’t wait to see her tracks! I am all the more curious as we have only a small number of tracks of females. Because phalaropes have reversed sex roles (except laying eggs, females do not contribute to incubation or chick care), females leave earlier than males, but also arrive earlier. With the growing number of tracks of females, we can investigate how females accomplish this early arrival (we already discussed this briefly in our JAB paper). Do they winter closer by? Do they migrate faster, or do they depart from the winter sites earlier than males?
Another bird with a geolocator, a remarkably pale male, and the partner of the female with the 2014 geolocator, remains to be recaptured. We will try again tomorrow!
Although we resighted three Dunlins with geolocators early in the season, we have failed to capture any of them. The valley where they were breeding last year is now virtually devoid of Dunlins (and Golden Plover). The last sighting of one of the geolocator-birds was in a flock of failed/non-breeders. Possibly, its nest was predated shortly after laying, when there was still a lot of snow. In Gelmetje, we did not see a single Dunlin this entire season, while the numbers in Björkfjället also appear low.
Sadly, Christian, Peter and Jesper, who have been of great help during the past two weeks, have left Ammarnäs. Only about a week to go for Morrison and me.
An ‘increase year’ was expected for the lemmings and other rodents in Ammarnäs. In such years, rodent populations slowly recover from a crash and build up towards a next peak. At such intermediate rodent densities, Long-tailed Skuas in Ammarnäs usually breed at least in the best area: Raurejaure.
Today we (Morrison Pot and I) crossed the tree line in Ammarnäs for the first time this season. After only about ten minutes the disappointment already sank in: this was going to be another non-breeding year for the Long-tailed Skuas. The second in a row, thereby repeating the pattern of 2012/2013. A pair was sitting quietly, occasionally picking some berries or insects. At this date, one of the partners should be incubating an egg…
The good news is that we resighted several colour-ringed skuas and all were still carrying their geolocators. Two birds have apparently switched partner, meaning two ‘famous’ birds are now missing: KJ, known for its extremely aggressive nest defense, and KM, a bird that we used to see on every visit to Raurejaure, as it bred at the ‘entrance’ of the area.
Another promising observation is that of a male Dunlin carrying a geolocator! Hopefully we will be able to recapture this bird. This bird is part of a big circumpolar effort to track the migrations of all subspecies of Dunlin – there are many!
Today, the 2017 field season started in Slettnes. After arrival, Hans and Rinse already had a first quick look in the colony and resighted some Arctic Skuas carrying geolocators. There seems to be lots of snow up in the mountains – not only in Finnmark but also in Ammarnäs. Morrison and I will not arrive in Ammarnäs until next week, so hopefully the snow will melt quickly in the coming days…
Our main aim is to recapture Arctic and Long-tailed Skuas, Red-necked Phalaropes and also Dunlins carrying geolocators so we can map their movement since the last year. Whether we can retrap them depends on whether they return to the same spot and whether or not they breed this year. We will know soon!
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.
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.