How to catch a skua with a chicken egg

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.

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Arctic skua eating a 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!

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the clapnet hidden under moss and the festive skua meal consisting of two chicken eggs and a sardine
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Geert with a skua lured with a chicken egg to the clapnet

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 !

Winter feeding red foxes harmful to breeding birds at Slettnes

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.

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pair of Arctic skua after they lost their nest

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!

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remains of a reindeer calf inside a red fox 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.

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how friendly they may look: in the current numbers they pose a threat to the birds at Slettnes

 

A dwindling colony?

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.

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From the 2017 report of the ICES Working Group on the Integrated Assessments of the Barents Sea (WGIBAR).

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.

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A one egg clutch: very common this year.

 

So this is our idea of how the bad food situation has affected the colony in the past few years at Slettnes:

  1. Because of the lack of food there are fewer host birds breeding in the area and feeding out at sea (kittiwakes and Arctic terns)
  2. As a results fewer Arctic skuas start to breed, resulting in a colony with a much looser structure than in good years
  3. 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).
  4. All this gives better opportunities for the Red Fox to enter the colony and predate the skua nests
  5. The skuas also produced smaller and fewer eggs in 2015-2017 than in 2014.
  6. 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.

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Circa 400 reindeer inhabit the area, potentially trampling nests.

A new season at Slettnes, Norway

We are back at our scenic study area in Slettnes in the far north of Norway. ‘We’ in this case consist of: Hans Schekkerman, Rinse van Vliet, Marc van Roomen, Janne Schekkerman, Geert Aarts and Ingrid Tulp. Goals for this year is to retrap as many Arctic Skuas and red-necked Phalaropes, with geolocators loaded with data of their whereabouts from the previous year(s), as possible. Last year was extremely early with first skua nests hatching already at 12 June, this year is the opposite. First nests are expected to hatch only at 28th of June. There was an exceptional load of snow in Northern Norway this year, the vegetation is two weeks behind a ‘normal’ schedule. But given that there is enough snow free area at Slettnes, this cannot be the reason for the late start of the skuas. Hopefully the loggers will reveal what kept them so long before arriving here. Up to now we only managed to recapture 4 skuas. We still miss a lot of known birds. Up to now we resighted 37 of the total of 73 birds colour-ringed in the previous years. Many of them still need to start breeding. Yesterday (13 June) we found several one egg nests that just started. All in all we have the impression that breeding numbers are considerably lower here in Slettnes in the period we are coming here (since 2014) than they were in 1998, when the last inventory was carried out. To check this idea, we are going to do a colony wide census this year, something we did not do systematically yet in the recent years.

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The red-necked phalaropes are at a more normal time schedule. Groups of males and females are on the lakes, twittering and chasing each other. Hormones are swarming around along the lakes edges! The first birds already have nests. We use a new method to catch the swimming phalaropes: a mistnet held flat between two persons immerged in the water just below the water surface, wait until the birds swim over it and then quickly lift the net from the water and flapping the bird! Yesterday we caught five birds within ten minutes this way. We already managed to retrap three loggered males (of which one unfortunately lost his logger).

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Also we have far more vagrant species than in any of the previous years, even a bee- eater made it as far north as here!

Slettnes: successfull field season despite low breeding numbers

DSC01292The season is coming to an end. At least for us staying in the area. There are still skuas with chicks, although not many. In total we recaptured 19 loggered Arctic Skuas and retreived their migration information over the last year. We gave all these birds new loggers and caught an additional 7 birds that also got loggers. Quite unexpectedly we got yet another logger back. The other day we met a British couple that were staying in the area already for a week. They were making a film on the nesting and hatching of a red-throated diver nest. They found one of our loggers with a bit of the blue ring attached. They picked it up but later put it down on a tussock, because they thought we put it there intentionally for some kind of measurements.

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our heroes: the UK couple with “the precious”

Then they ran into Barbara Ganter and Hans-Ulrich Rosner, our fellow researchers working on Dunlin in the area, who told them that we would be extremely interested in getting the logger back!When we met the couple they had just spent 2 hours searching for ‘the precious’, but could not find it back. Together we searched for another hour systematically and checked every tussock in an area the size of a quarter football field. Just at the point when we were about to give up, one of them found it back!! The couple was so relieved! And they were the heroes of our day of course! That brings our total to 20! Last year we ringed 53 birds. It is clear that a large part of those either did not return, did not breed, or whose eggs hatched before we had a chance to catch them. One of the things we will dive into in the analyses if the El Nino may have had any effect on the early breeding season for some pairs or the lack of breeding for other pairs.

Left: Four-year-old Arctic Skua with still some barred feathers. Right: The most exciting time of the day: reading out retrieved loggers!
Left: Four-year-old Arctic Skua with still some barred feathers. Right: The most exciting time of the day: reading out retrieved loggers!

We are also seeing back the first birds that were ringed as chicks in 2014. That was a very good breeding year resulting in some 100 chicks ringed of which a large proportion also colour ringed. They do not breed yet, but hang around and sometimes seem to team up with a breeding pair.

In contrast to other areas in Europe we had extremely good and warm weather. Yesterday it was even 27 degrees! The caretaker of the lighthouse told us that no one in the nearby village Gamvik could remember that such temperatures were ever recorded before! Even swimming in the Barents Sea is not an achievement anymore.

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Lighthouse in Mediterranean weather!
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Announcement of talk by Hans.

On last Sunday Hans gave a presentation at the lighthouse for locals of Gamvik and tourists. It was well visited and it was striking to notice that people do not seem to be aware that they are in a very special place, home to the largest colony of Arctic Skuas! We are leaving Slettnes now and will return next year to meet up with our world travellers once more.

 

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Pair of dark phase Arctic Skuas, both with loggers.

Food shortage at Slettnes

vole regurgitated by by skua
vole regurgitated by skua
very tame Arctic skua
very tame Arctic skua

You wouldn’t think we are at 71°N, with today’s temperature: 22°C, warmer even than in Rome and hardly any wind. This means mosquito bonanza!

Nearly all Arctic Skuas have hatched by now, but we have seen no chicks older than 1 or 2 days and several nests with dead chicks. The feeling that the food situation is bleak this year settles in more and more. Arctic Terns are not breeding either and one skua threw up a vole. The outskirts of the colony are either vacant or birds hang around but have not produced eggs.

The only breeding pair of Great Skuas lost their chicks within a few days, another sign that even they cannot feed their chicks. The logger information shows that the breeding Arctic skuas go out to sea sometimes for more than a full day leaving their partner at the nest.

In the meantime we managed to recapture 19 individuals from last year. It was a struggle against time, since many nests hatched so early. Catching them on a nest with a chick does not seem to work at all. Apparently the chicks need less brooding than e.g. waders and if we take the chick away they won’t return to the nest to sit on the egg left. Also we found out there are at least 50 ways why the catching fails, despite the fact that the snare system works well in principle. Either the battery power is too low, the bird simply escapes, the distance is too far for the remote control, the bird won’t sit down or in the worst case, the coil of the snare is broken.

The loggered birds showed the same variation as last year, wintering in south-America, South Africa, the Caribean, West Africa and one even off the coast of Spain. Of the four couples we recaptured the partners each went their own way, so they probably meet each other only here on the breeding grounds again.

On the Red-necked Phalarope front we also had some successes: 4 recaptured birds. One loggered bird lost its logger and one lost its nest, making catching impossible. Three of them went to the Arabian Sea, one even as far south as Mozambique. Of two of the birds we had tracks from last year. The tracks in the consecutive years were nearly copies!

dead Arctic skua chick
dead Arctic skua chick found in a nest

Strange season at Slettnes

DSC00715After five days in the field we are more and more puzzled about this season. We had the first Arctic skua chick yesterday, which is extremely early, and many more nests are about to hatch. These birds must have started laying eggs mid May! Also the Fieldfare chicks nesting near the lighthouse are about to fledge and the vegetation is two weeks ahead. At the same time many skua territories of last years are not occupied and in many territories birds are just hanging around. We also still find nests that were just started. The Red Fox is present again and indeed we found two nests predated already.DSC00733

Up to now we recaptured 7 Arctic Skuas and their loggers show the wide variety we are used from them: wintering in south America, South Africa and the Caribbean. The 4 out of 7 that we recaptured last year as well, took remarkably similar routes.

Today was rainy with 6/7 Beaufort, not really weather to catch skuas. Besides we had some troubles with our catching device, the snare. It is quite ingeniously constructed around a remotely controlled vacuum cleaner spring, but now it needed some special technical attention (and a new set of batteries as it turned out later). Nevertheless we went outside to check territories at the outskirts of the area and look for Red-necked Phalarope nests. Tomorrow is going to be sunny and the day after even 15 degrees! Time for a dive in the Barents Sea!