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.

 

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Red fox captured by a camera trap
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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…

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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.

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

Red fox makes life impossible for skuas (and biologists) and divorcing royal skuas

We thought we already experienced the worst breeding season ever last year, but 2018 is even worse. While last year’s eggs survived for several days before they were eaten by the fox, this year nests are predated even before a second egg is produced. Also our activity does not seem to matter: whether we visited a nest or not, in most cases they are predated overnight. Only the nests near the lighthouse seem to stand a chance. That also limits our possibilities for retrapping loggered birds greatly. So far we retrieved 6 loggers, with only one remaining chance of retrapping a loggered bird that still has a nest. We hope that many pairs will try a second time, since it is still early in the season. Indeed, we still find new clutches from time to time, and yesterday evening we were lucky to find the nest of EG, featured in the previous blog post, with a freshly laid egg. Within ten minutes we managed to retrap her and removed her logger!

To confirm that it is really the fox taking the eggs, we placed three camera traps near skua nests. We also found out which fox den is active (a mother and two cubs) and put a camera trap near the main opening, hoping to record what prey are brought to the nests.

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placing a camera trap near the fox den

Apart from the fox, also the ravens are very active and might partly be responsible for the disappearing eggs. There is a nest on the walkway at the top of the lighthouse. From here, it has a perfect vantage point to oversee the area and spot incubating skuas…

Then it is time for some gossip! A much appreciated pair, with colour rings EE and SD, has been together since 2015. We named this pair after our royal family Maxima and Willem-Alexander, because EE winters in South-America and SD is the only bird in our sample that stays within Europe during winter. The sad news is… they separated! EE not only lost her logger, she also switched partners and is now together with JO in a different territory. JO is also a handsome fellow that winters off the coast of west-Africa. SD stayed in his old spot and has paired up with an ‘unknown’ (no rings) light morph female. However, both EE and SD seemed to have lost their clutches in an early stage, or did not lay at all.

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EE (Maxima on the right) with her new partner (JO)

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!