Over the next weeks, we will blog again on this site to keep you up-to-date about our fieldwork in Ammarnäs (Sweden) and Slettnes (Norway).
In Ammarnäs, the team will focus on Long-tailed Skuas, which may finally breed again after three non-breeding years. Rumors about reasonable to high rodent abundances have reached us during the past months, so fingers crossed rodents are still abundant at the time of writing, when the skuas should just have started laying… If so, we finally get the chance to retrieve the 20+ geolocators that have been deployed during the previous breeding season, in 2015. Another project in Ammarnäs, that started last year, is focusing on Dotterels and is led by Christian and Tim.
In Slettnes, Ingrid and Hans will – for the sixth year – follow the whereabouts of the Arctic Skua colony. Main focus will be on reading colour-rings to further refine our survival estimates, survey the colony to see if the 50% decline over the previous two decades is continuing, monitoring breeding effort and success, and retrieve geolocators. Let’s hope they are doing better this year than during the previous disastrous years!
Both in Ammarnäs and Slettnes, first teams arrive on 10 June. Watch this space!
In October 2015 at the 2nd World Seabird Conference in Cape Town, South Africa, an international collaboration was started to combine geolocator tracking data of Red-necked Phalaropes from breeding sites across the Western Palearctic. Now, a joint paper is published in Frontiers in Ecology and Evolution, showing a migratory divide between populations from Greenland, Iceland and Scotland migrating to the eastern Pacific, and populations in Fennoscandia and Russia migrating to the Arabian Sea. Especially the western route to the Pacific is amazing – a migration route not shared with any other Western Palearctic species. Phalaropes using the two routes and wintering areas differ in migration strategies and also in the amount of movements within the wintering area. Only few studies have shown such diversity in movement strategies among subpopulations within a species.
It has been a tremendous job to collect all this data, especially because Red-necked Phalaropes are far less site-faithful than, for example, Long-tailed Skuas, albatrosses or other seabirds. Out of 10 geolocators deployed, on average 3 were resighted and recaptured. Even if recaptured, things can go wrong: some loggers failed prematurely and others were lost. Considering the effort required for each and every logger, the paper is also a testament to the willingness of people to share their data and the power of international collaboration!
Hence, thanks to all collaborators, in particular Yann Kolbeinsson, Olivier Gilg, Jose Alves
Malcolm Smith, Aleksi Lehikoinen, who led the fieldwork at the other sites.
Hans and I arrived back home last Friday, after a field season at Slettnes with very interesting but also alarming results.
Until this season, we hypothesized that as long as the food situation is good, the Arctic Skuas would be able to withstand the predation pressure by foxes: skuas would breed in higher densities and be more aggressive. However, this years’ results shows we were wrong. Food situation was obviously very good: huge feeding frenzies of Black-legged Kittiwakes, Herring Gulls, Arctic Terns, other seabirds and marine mammals were feeding on pelagic fish just off the peninsula. Arctic Skuas were obviously taking advantage of this. To get an idea what this feeding activity at sea looks like, please have a look at this video of the near-shore gull activity (and a whale, see if you detect the blows!) and another one below showing four species of skua (both videos compiled by Hans).
Despite the good food situation, the number of breeding pairs did not increase relative to the preceding poor years. Also, aggression levels remained mediocre. And, as already reported in earlier posts, predation rates were high again. Most nests survived for only a few days before disappearing. Contrary to previous years however, many skua pairs produced a second clutch, but many of these clutches were also predated within a few days.
What could explain the high predation rate despite the good food situation? One hypothesis for these patterns is that one fox (or a few?) have specialized on finding Arctic Skua eggs over the past three years. Specialization is impossible to prove with the data available, but one expectation that we can verify is that the same individual fox should reappear in our nest camera pictures. If indeed foxes have specialized on skua eggs, shooting foxes would help decreasing the predation pressure at least until new individuals get specialized.
Lots of news to report from Slettnes! We are enjoying much activity at sea, where huge feeding frenzies of gulls (mostly Black-legged Kittiwakes and Herring Gulls) feast on pelagic fish together with Minke Whales and occasionally joined by White-beaked Dolphins, Humpbacks and Fin Whales. Many skuas (including migrating Pomarine and Long-tailed Skuas, plus the locally breeding Arctic Skuas) join the party as well. The Arctic Skuas seem to do very well in obtaining food.
Fox caught red-handed
On land however, things are not going that great for the Arctic Skuas. As reported before, most freshly laid clutches disappear after one or two days. To find out who takes them, we deployed camera traps at skua nests. Although it seems that nests with cameras are less quickly predated as other ones, we managed to capture two Red Foxes in the act of taking skua eggs! See below…
27 years old male Arctic Skua
Yesterday, we captured a male with a somewhat worn metal ring and a ring number that clearly didn’t belong to the series we have used since 2014… It turns out this bird has been ringed on 3 July 1991 as a chick at Slettnes, by Karl-Birger Strann. Actually, it was amongst the very first Arctic Skuas ringed here by Karl-Birger. By coincidence, the next colour-ring on the string read ‘KB’!
Seabirds typically have a slow reproduction but can get pretty old. In fact, the oldest confirmed wild bird is a seabird – a Laysan Albatross of over 60 years called ‘Wisdom’. For Arctic Skuas, the longevity records for European birds lists a 31-year-old Finnish bird as the oldest known individual, with an Icelandic 26-year-old bird as a second. Hence, KB beats the Icelandic bird, and if it manages to survive some more years, maybe it will beat the Finnish as well? We’ll see…
Logger retrieved of a tough phalarope male
When Slettnes finally experienced a day with calm weather last week, Hans and I went out ‘phalaroping’: catching Red-necked Phalaropes using a mistnet. We captured several birds, and were surprised to even capture a male carrying a geolocator! To our surprise, this bird already carried a geolocator during 2015-2016, and got a new one in 2016 that we now retrieved. After three years, it was finally released of its 1.0g logger!
Virtually all geolocators of Red-necked Phalaropes were retrieved one year after deployment, with a few after two or even three years. Two or more years of data from the same individual allows us to study the consistency of individuals in their movements. In Red-necked Phalaropes wintering in the Arabian Sea, this is especially interesting because this area is known for its high variability in where and when food is available. Most Red-necked Phalaropes seem to respond to this variability by moving a lot, except a few – including this bird… The question is: are these movements individual strategies repeated every year, or are they flexible responses to current conditions, changing from year to year?
Unfortunately, after two years the battery of these geolocators is empty, which made it impossible for us (but not for the manufacturer) to download its data. While we wait for this, please have a look at this video (in Dutch) in which we take off the logger and show the track of this individual from 2015-2016.
After a very windy first few days at Slettnes (without our luggage) weather somewhat improved. For the Arctic Skuas, improvement is however not (yet) apparent when it comes to the predation compared to last year: several eggs disappeared right after laying (also nests that we did not visit). This complicates the field work considerably, because our main aim, catching as many birds with geolocators, becomes difficult if the birds have no nest.
However, the good news is that food availability seems to be somewhat better than during the previous years. We deduce this from the foraging activity out at sea, where flocks of gulls and Razorbills were actively feeding over the past days. Also, the few skua eggs that we measured are slightly larger than in the past three years. A good food situation should also be reflected in the body mass of the skuas. From the two individuals that we recaptured (one carrying a geolocator), the female ‘EU’ was indeed heavier than ever: she weighted 508g, 466g, 455g in 2014, 2015 and 2016, respectively, and weighted 534g this Thursday! However, the other bird, ‘EY’ (a male, thus lighter anyway), had a weight similar as in the other years (391-428g in 2014-2016, and 412 this year).
In the coming days, we are hoping to retrap more birds with geolocators. As the batteries of the loggers are running out (most were manufactured in 2014-2015), they will stop recording soon, if they not already did so. Over the past years, we obtained multiple years of data from quite some individuals, and now they will finally be released from their loggers!
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).
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!