New paper: dramatic decline of the Arctic Skua colony at Slettnes

We haven’t been able to go to Slettnes during the last breeding season in 2020 and 2021, hence the paucity of blog posts here. However, there is some news to report: our paper on the dramatic decline of Arctic Skua numbers at Slettnes has been published in Bird Study!

The first year that we worked in Slettnes, 2014, was a good year for the Arctic Skuas. Losses due to predation were few, food was abundant, and consequently, many pairs managed to raise chicks. Since then, almost no chicks fledged from the Slettnes colony, and the number of breeding pairs dwindled.

In our paper, we collated virtually all data that we collected during 2014-2019: nest counts, clutch and egg sizes, adult body mass, daily nest survival rates, annual apparent survival rates of adults, levels of aggressiveness in nest defense, the time spent at sea (from the geolocator wet/dry sensor), number of adults at the territory, fox sightings, and camera trap photos. We combined our data with data collected during 1997-1998 by Kirstin Janssen (Arctic University of Norway, Tromso). During 1997-1998, Kirstin found more than 175 nests per year and estimated the colony to hold about 250 breeding pairs. Some 20 years later, this number has halved… and I fear that numbers will have gone further down in 2020-2021.

In the paper, we argue that the decline is likely due to a combination of low food abundance and increased predation by Red Fox. Nowadays, even in years with high food abundance, Arctic Skuas at Slettnes may not be able to reproduce due to the high predation pressure.

You can find and read the paper here (open access).

Caught by cameratrap: Red Fox taking egg from an Arctic Skua nest in the reflection of the midnight sun, while one of the adult skuas dive-bombs the fox. Time of the crime: 01:38.

Major seabird hotspot in the North Atlantic

Migratory birds depend on multiple sites, sometimes separated by thousands of kilometers and across many countries. Conserving all sites used by migratory birds is challenging, especially for species that use oceanic areas on the ‘high seas’. The first step is identifying these areas.

A collaborative project led by Tammy Davies from BirdLife has shown that an area in the North Atlantic – of which already was clear that it was of huge importance to Long-tailed Skuas – is also used by many other seabirds. In total, an estimated 5 million birds use this area annually! Obviously, this area needs to be protected. A proposal to designate this area as a Marine Protected Area is now considered by the OSPAR committee.

For this analysis, geolocator data of Long-tailed Skuas from Ammarnas has been used. The paper, published in Conservation Letters, can be read for free here.

Figure from the paper, showing the origin of seabirds using this hotspot in the North Atlantic.

Geolocator data from Ammarnäs and Slettnes part of AAMA study published in Science

Last week, a paper in Science presented the Arctic Animal Movement Archive – a collection of animal movement data from the Arctic, hosted by Also geolocator data obtained in Ammarnäs and Slettnes – from Arctic Skuas, Long-tailed Skuas and Red-necked Phalaropes – are part of the AAMA. The paper can be found here (please get in contact if you can’t access the paper…).

Tracking data from several decades, many species, and across the Arctic and subarctic region are included in the AAMA. This allows studying changes in movement patterns at large scales and across species – which is highly relevant in the face of a rapidly warming Arctic… In the Science paper, several case studies are presented showing long-term and large-scale changes of animals in their movements.

The publication of the paper sparked quite some media coverage:

30 October: Robs’ public defence

Dear all,

After five PhD-years, 13 field seasons and walking several thousand kilometres across the tundras of Ammarnas and Slettnes, I am very happy to announce that on 30 October, 11 AM, I will defend my PhD thesis entitled ‘Seabirds linking Arctic and ocean’ in the aula of the Wageningen University, Generaal Foulkesweg 1, Wageningen.

This is a public event, so anyone interested in skuas and phalaropes, or seabirds in general, is warmly invited!

Thanks to all who have helped me to get here. It has been an incredible journey!

All the best, Rob


Common Ringed Plover geolocator study in Ammarnäs

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.

Nest searching around Båssajaure.

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.

Nest of common ringed plover.

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.

A Wolverine!

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?

Linus Hedh

A Common Ringed Plover with a freshly deployed geolocator.

Final sweep up at Slettnes

The short field season has ended at Slettnes, both practically – because we left the area after two weeks – but sadly also for the birds, because we must conclude that also the 2019 breeding season failed completely. None of the colour-ringed birds we resighted managed to prevent foxes from taking their eggs, but also unknown birds (to us) failed to do so. Because working in the field and approaching nests always carries the risk of leaving traces which might lead potential predators to nests, we also recorded nest fates of nest that we did not visit, but only observed from a distance. Also those nests disappeared within a few days after laying the first egg.


Red fox captured by a camera trap

Hans holding ‘Spotty’, the dark phase skua with the typical white spots on its wings

So what did we learn from this season? The plans of this final sweep up season for Rob’s PhD project was to try to recapture as many as possible of the loggers that we put out in 2014-2016 and still had not recaptured, read colour rings to see who returned, and to get a general impression of the success of the breeding season. Well the breeding season was (again) quite dramatic, due to low food (fish), not only near Slettnes, but also in the Varangerfjord, where the arctic terns and kittiwakes apparently left their colonies due to food shortage (as we heard from Tomas Aarvak of Birdlife Norway). Our birds laid relatively small eggs and apart from two pairs, all clutches consisted of one egg only. Either because they were not able to produce more than one egg, or their nests were already predated before they managed to lay the second one. In combination with the high fox activity, not a single chick was produced this year. With a lot of effort we managed to recapture six birds and relieve them from their loggers, and we identified 37 other individuals by their colour rings, that will contribute to estimates of annual adult survival rates. Survival in these skuas is high; a typical adult life span is about eight years. As to replace itself each bird has to produce only one son or daughter in this period that becomes a breeding adult. This means that even a few lost breeding years in a row may not be a problem for the population. However, every once in a while the birds should be successful and in such a year all things should come together: enough food, low predation rates and enough birds in the colony to enable a successful defence against predators. With the declining number of breeding pairs at Slettnes such a window of opportunity is urgently needed. Here the last truly good year is now as long ago as 2014. Indeed, this season we encountered several skuas ringed as chicks in 2014 for the first time as adults in the colony. Fingers crossed that these may breed successfully in the years to come…

ZA, ringed as a chick in 2014 and now returned to the colony

Late year at Slettnes Arctic skua colony

Late season at Slettnes

Sometimes a biologist feels like Sherlock Holmes. Every breeding year in the Arctic is different, but how come the skuas are so late this year? We are here for over a week now and only today at 19th June the majority of the skuas start to lay eggs, roughly two weeks later than on average. Did they really only start now or did they try before, but were their eggs taken by foxes or other predators and is this the second wave? It is difficult to find out, but given the high predation rates the latter may well be the case. Also the food situation does not seem to be brilliant, with low feeding concentrations of seabirds at sea indicating that there is not a lot of fish out there. It does not resemble last year at all  when masses of birds were feeding out at sea.

To discover who is taking skua eggs we placed eight camera traps at different nests. The camera responds to movement, that can be either cause by the incubating bird, a predator or a reindeer moving through the area. Somehow the camera traps seem to protect the nests as we have the impression that nests with camera traps survive longer than those without. At the only one (so far) in which the egg disappeared the picture says it all and gives a nice summary of life at Slettnes: the midnight sun, a skua taking off and a red fox stealing the egg in the middle of the night. If skuas have no nest, catching them to retrieve loggers is practically impossible. But despite high predation rates, we managed to catch back three birds, of which one has a logger that contains data since 2015! Now that more birds with loggers started breeding we have more opportunities to retrieve loggers of birds that we failed to catch last year because they lost their clutch.

caught by cameratrap: fox taking egg of Arctic skua nest in the reflection of the midnight sun. Time of the crime: 01:38


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.

Norwegian Lemming (Lemmus lemmus) in Björkfjället.

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.

A very unusual nest location (of AF/KR), on top of a rock!

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!

Long-tailed Skua happily breeding.

New field season approaching

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!