In less than a month, a new field season will start in Ammarnäs and Slettnes! We are all excited to get up there during what will be the last field season within my PhD project on the long-distance migration of Arctic seabirds, but hopefully/probably not the last one ever.
In Slettnes, our aim is to continue the work from previous years: retrap Arctic Skuas with geolocators and monitor their breeding activities. The geolocator tagging has revealed extreme migrations across the Atlantic and we are currently working on publishing these results. Very exciting stuff! Hence, we are hoping for a good breeding year, allowing us (Hans, Ingrid and me) to increase our sample size some more by recapturing many tagged individuals.
We have been concerned about the apparent large decline of the Arctic Skua colony over the past two decades (see this handout). Our hypothesisis is that the skuas suffer from the combined effects of an apparently bad food situation for seabirds and predation pressure by Red Foxes on the Arctic Skuas. Foxes do not only feed on skua eggs, but even manage to take adults, as was shown last year by a Red Fox photographed while holding a dead Arctic Skua (carrying a geolocator) presumably to its den. To better document the activities and prey spectrum of foxes, we will bring some camera traps that we plan to deploy at fox dens.
In Ammarnäs, Tim van der Meer, Christian Hoefs, Morrison Pot and Peter Antkowiak and others will take care of the work. They are preparing themselves for a busy year, as a lemming ‘increase-year’ is expected. This means lemming numbers are growing but not yet peaking. Lemmings were virtually absent during the last two years, causing Long-tailed Skuas to skip breeding. This year, skuas are expected to breed and the team will try to find as many nests, read colour-rings, and recapture birds with geolocators, as they can.
Otherwise, some interesting side-projects will be ran: Tim and Christian have the ambitions to start a study on Dotterel – a species so beautiful it is almost a miracle, and with an interesting migration. In addition, we are taking part in two circumpolar initiatives: one on migration of Dunlin (meaning some more geolocators should be retrieved) and the other on Arctic food web interactions (with nest predation of waders as a central theme).
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 we catch skuas on their nest. They are very motivated to incubate their eggs, so they will always want to return to their nest. Our catching devices are all designed to catch the bird when it sits on its eggs. So it is very frustrating if you can’t catch the birds back anymore, simply because they lost their eggs. Out of this frustration Geert got the idea to try to lure the skuas with a chicken egg and canned fish. The first bird he tried this on was immediately attracted and started to eat the (raw) chicken egg.
The day after we tried several catching devices, a ball chatrie, a piece of netting on the ground with lots of nooses for the bird to get trapped in, our normal catching device with a remotely operated noose and a clapnet with a chicken egg attached to the trigger. The last method really worked, although the bird managed to gobble down the whole egg (boiled this time, so it would take longer to eat the whole egg) without triggering the clapnet. Then we decided to trigger the clapnet with the remote controller and caught two loggered birds, not on their nest but lured by a festive meal consisting of canned sardines and chicken eggs!
We tried the method on more birds, but the trick only worked for two birds. Since nearly all birds lost their nest, some of them are no longer on their territory. That brings the total of retrapped Arctic skuas to 11, plus one logger apparently lost by a skua, that we found back on the tundra by chance !
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.
It is late June and skua nests should be hatching right now, and one should stumble over chicks on the tundra. Instead pairs are hanging around with nothing else to do than sit at their territory and fly to sea to feed from time to time. Of a total of 40 nests, 33 were predated by red foxes, two more by gulls. In the four years we have worked here so far, we never encountered such high predation rates. One could argue that foxes follow our tracks and we as researchers lead them from nest to nest. Even though we are very careful at nests, our scents will definitely play a role. However also nests that we did not approach, but only observed from a distance disappeared. And all nests disappeared very shortly after they were started. Not only the skuas, but also waders in the area suffer from fox predation. Barbara Ganter and Hans-Ulrich Rösner, who have investigated the Dunlin population here over 25 years, also see more predation than usual.
We visited the active fox den in the area and it made an impression of a lavishly set table: parts of a reindeer calf, remains of several gulls, feathers spread out all over the place. Four nearly full grown young foxes are regularly playing outside the den. A fox den has several entrances and a few were stuffed with even more food: a reindeer calf and a complete cormorant. We guessed the 66 skua eggs were also hidden somewhere inside the den!
And foxes are not the only threat: because of late snow melt the reindeer herd could not feed in the mountains and arrived here extremely early and in much larger numbers than usual. Now 600 reindeer cross the area on a day to day basis. Not only can they trample nests, they will eat eggs if they come across them. Resting herds are often found lying in the middle of known skua territories for hours, preventing them from going back to their nests.
We are working in the Slettnes Arctic skua colony since 2014. That year nests were abundant, skuas were aggressively attacking us, and many chicks survived and fledged. The seasons since then have been worse every year. Less nests, less known birds resighted and hardly any breeding success. The main driving force behind these changes seems to be food availability. Arctic skuas do not feed for themselves, but rely on host species such as Arctic tern and kittiwake. Skuas chase their victims until they throw up the fish they just swallowed. There are no consistent monitoring programs on Arctic skuas, but the kittiwake is in strong decline all along the Norwegian coast (see this NINA report). We counted no more than 80 breeding pairs of Arctic skua in the Slettnes colony last week, while there used to be 250 in 1997/1998. The key food for seabirds, but also for large fish and whales in the area are capelin and herring.
Capelin underwent several collapses and rises since the 1980s. The stock estimate is based on the joint Russian–Norwegian acoustic surveys in September each year (see this report). During winter and early spring Barents Sea capelin migrate to the coast of northern Norway (Finnmark) and the Kola Peninsula (Russia) for spawning. During summer and autumn capelin migrate north- and north-eastward for feeding. The last collapses were caused by poor recruitment, most likely in combination with low growth and increased predation pressure. The 1986 collapse was aggravated by high fishing pressure. Since then fishing pressure has been low. Predation by young herring has been suggested to have strong negative influence on capelin recruitment. The recent strong decline in the capelin stock appears to be caused by a combination of the same factors as in the previous capelin collapses: a decrease in individual growth rate of capelin, increased mortality caused by heavy predation from the large cod stock, and lower recruitment. In 2016 there was better recruitment of both capelin and herring, which could have led to a good food situation in 2017. However we have not witnessed that so far. For bird species relying on pelagic species, also the distribution of the fish is important: it should all be within reasonable flying distance of the colony.
So this is our idea of how the bad food situation has affected the colony in the past few years at Slettnes:
Because of the lack of food there are fewer host birds breeding in the area and feeding out at sea (kittiwakes and Arctic terns)
As a results fewer Arctic skuas start to breed, resulting in a colony with a much looser structure than in good years
Arctic skuas are also less aggressive towards predators because they are in worse condition (the body mass of birds that we captured every year is 5% lower in 2015-2017 than in 2014).
All this gives better opportunities for the Red Fox to enter the colony and predate the skua nests
The skuas also produced smaller and fewer eggs in 2015-2017 than in 2014.
The increasing reindeer herd further aggravates the situation: ca 400 animals wander through the area every day, possibly resulting in trampling of nests (and they will also eat eggs when they come across them).
Of course we have also considered our potential disturbing role as researchers in the area. However, especially in parts of the colony where we did not work, the decline is even more prominent than in the area where we caught most birds and spent most time.