Last Sunday morning, Ingrid and Rob were interviewed for the Dutch radio show ‘Vroege Vogels’ about our (tracking) studies of skuas and phalaropes. You can listen to by clicking this link.
This is my first contribution to this blog and thus my first visit to Ammarnäs in June. But more importantly my first real field work season in the area. Finally! Between the 10th and 27th of June I, together with a master student, had the pleasure to work with Common Ringed Plovers (Charadrius hiaticula, see below for a picture) in Björkfjället. The aim for the work in Ammarnäs is to compare migration patterns of the population breeding in the mountain range with those breeding in the milder, coastal areas on the same latitude. Our coastal study site is the island Malören, which is located in the middle of the Bothnian Bay. By comparing those sites we will be able to control for geographical latitude and distance to the nearest possible wintering grounds. The idea is to better understand how differences of the annual cycle, such as onset of breeding and length of the breeding season, affect the migration distance and timing. And vice versa. The study will be conducted over three years by deploying light level geolocators and monitor the onset of incubation at each site. Apart from this we are also interested in changes in onset of breeding in the mountain range over the past 50 years.
Arriving to Ammarnäs this early in the season was thrilling. Snow was still covering much of the tundra and Ammarfjället, which is situated on higher altitudes. But regardless, up there, life is already coming back and multiplying. The first day was a warm up. We joined Rob and Morrison (the Skua team) to Gelmetje for some skua catching. The day after we took our first steps up on Björkfjället to find a suitable area that hosts high enough densities of breeding ringed plovers. Finding such areas will make the upcoming seasons, when the geolocators are to be retrieved, much easier. That day we went Ruohtakvàggie (Ruohta Valley) which consists of a chain of lakes, making it a potential good area. Coming out to a new potential study site is always exciting, but there is also some anguish. Especially since the only background information we had was that plovers occur, but no further information about densities. I must say that I felt very discouraged and crestfallen after that first day. The general area was vast and suitable plover habitat was scattered all over the place. Partly because of the geophysical properties of the area, partly because of the snow cover. Also, we only saw a few ringed plovers and neither of them showed any sign of having a nest around.
The next couple of days were better. We decided to reconnaissance in an area further east, around Båssajaure (Lake Båssa). Initially we did not find many plovers. Actually, we had better luck with mammals. In a distance, out on the ice of an unnamed lake, we spotted something brown lumber around: a wolverine!!! The beast could be seen for 45 minutes as we slowly approached, carefully searching the slope facing the lake for plovers. In the end we were only 150 meters away before it decided to cross the lake to continue to search for food on the other side. As we continued forwards we found the first two plover nests and the first geolocators could be deployed.
After that we realized that we had found our spot. During three overnight trips, we were able to locate 12 nest and catch 23 plovers, which all were fitted with geolocators. On the best day we tagged no less than six birds within 8 hours! Now the long wait starts: will the birds be back next year?
Its been just over a week that Morrison and I arrived in Ammarnäs. Our expectations were high: there had been rumours about high lemming numbers over the past weeks and months. But we also had some concerns: did the lemmings survive warm periods with rain in early spring?
After arrival in the early morning of 10 June and a nap, we went up to the main Long-tailed Skua study area: Raurejaure, to explore the first part of the area. Our heart sunk when the skuas that we encountered were hardly alarming or defensive, and we were unable to locate any nests: was this going to be yet another non-breeding year? I couldn’t quite believe it! Normally, there are about four pairs in the area that we checked; now there were only two pairs present.
Next day things were looking much, much, much brighter! Up in Gelmetje, we found several nests, including two of birds with geolocators of which we retrieved one. From then on, it just got better and better. Nests of skuas carrying geolocators were found, and we were very successful in trapping these individuals. At the time of writing, one day before we leave Ammarnäs, we retrieved 15 geolocators! Tomorrow morning we’ll do our final attempt to trap SV, the final loggerbird that we failed to catch so far…
So why didn’t we find nests on the first day? One reason is, that the first pair we encountered nested on a very unusual location: on top of a big rock. This is so unusual, that I blindly assumed the bird that was sitting there wasn’t incubating… Another pair, further into the area, had a very similar nest location. Reportedly, snow cover had been extensive into the first days of June, that is, when Long-tailed Skuas lay eggs. Apparently, these birds selected the first parts that became snow-free. Still, we haven’t even seen this in 2015, when snow melted even later.
Another remarkable phenomenon we have encountered this year more than earlier years, is change of partners and territories. For example, AF had been breeding up on a large hill since 2007, but has now much downhill to pair up with KR, the former partner of KJ. NZ changed location about 1 km to pair with KO, that used to be with KG. In each case, males kept their territories but females switched partner and therefore territory.
Regarding the results of the geolocator tracking: that has to wait. All batteries are flat, meaning we’ll need to send them to the manufacturers to download the data. If we are lucky, together they may contain 31 full annual cycles! Fingers crossed…
So, finally a breeding year for the Long-tailed Skuas in Ammarnäs!
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.
Please read the full paper here.
A paper I wrote with Rohan Clarke, Peter Pyle and Kees Camphuysen has been accepted for publication in The Auk, the journal of the American Ornithological Society! It can be downloaded here and is titled “Timing and duration of primary molt in Northern Hemisphere skuas and jaegers”.
The paper presents estimates for primary moult timing and duration in all four northern hemisphere skuas: Great, Pomarine, Arctic and Long-tailed Skua, including multiple age-classes (for as far as they are identifiable…). Moult data is difficult to obtain for oceanic wanderers like skuas, as they perform their moult at sea where fieldwork is costly and capturing seabirds is ‘challenging’, to say the least. Recently, people realized that molt data can be obtained from (digital) photography. With a growing popularity of bird watching, bird photographing, pelagic birding trips, and the sharing of large numbers of images over the internet, a very comfortable and cheap way to collect data has emerged. Over the past years, we collected photos of nearly 2000 individual skuas, photographed at sea or near-shore by about 600 photographers. Many photos were found at online sighting portals like www.waarneming.nl and ebird.org, but we were also greatly helped by many people sharing their pictures through e-mail. From these pics, we inferred the primary moult score and subsequently estimated three moult parameters: the mean start date of moult, the standard deviation in this start date, and the mean moult duration.
What we found in this study is that, as expected, larger species took longer to moult, but this also meant that larger species had a hard timing in avoiding temporal overlap between moult and migration. In general, migratory birds avoid overlap of moult and migration, but we found that Great Skua moult throughout its autumn migration! A rare strategy, possibly facilitated by a very low migration speed through an area with good food availability. Another interesting find is that among the three smaller species, their very first moult cycle took longer than later ones. As soon as they started migrating, moult cycles would run more or less parallel to adults. We suggest that this shorter moult cycle reflects a time constraint set by migration.
This study would not have been possible without all photographers willing to share their pictures. A huge thanks to them!
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.