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)
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First glimpse of breeding conditions at Slettnes

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).

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EG in windy conditions.

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!

New release on survival and growth of Golden plover chicks

Last february our last paper was published in Behavioral Ecology and Sociobiology.

We want to share this work with you. In this paper we studied the growth of golden plover chicks by radio-tracking individuals from hatching till fledging and related variation in chick growth to food availability (as sampled by pitfall trapping) and weather conditions. Very interesting for as we found notable differences among years reflecting a higher importance of food availability than weather conditions on the growth of the chicks.

We invite you to discover all the details by reading the paper! You can find it here !

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Golden plover chick with radiotransmitter

The new field season is approaching!

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).

The best bird of the season happened to be a mammal

This years’ field season has ended! Geert and Ingrid left Slettnes and Morrison and Rob left Ammarnäs on 2 July. Despite the poor breeding season for both skua species, some valuable data and observations have been collected. In total, 14 geolocators have been retrieved from Arctic Skuas, some with 1.5 years of data on some of them. The Long-tailed Skuas of Ammarnäs will have to wait another year before they can hand in their geolocators.

As I wrote in the previous blogpost, we have recaptured several Red-necked Phalaropes with loggers: 4 in Slettnes (1 female) and 4 in Ammarnäs (all females). One was deployed in 2014 and another in 2015 and they should have more than one year data. The high number of females is exciting (see my previous post).

Unfortunately, we have been unable to recapture any of the eight geolocators deployed last year on Dunlins, although we resighted three of them early in the season. High predation pressure, shown by both an artificial nest experiment (using quail eggs in fake nests to measure predation rate) and monitoring of Dunlin nests, is the likely explanation of this failure. Hopefully they return next year again!

On our last day in Ammarnäs, we went up to Björkfjället to finish the artificial nest experiment. We also wanted to see the Shorelarks, a species that has declined tremendously in the Swedish mountains. We were also hoping to catch a glimpse of the Wolverine that Martin saw a few days earlier. After a failed attempt to see this mysterious species, one of the large European mammalian predators, we didn’t really expect to find it. Then, at a distance of ca. 3km, I noted a Wolverine running downhill to a Reindeer carcass (with a White-tailed Eagle feeding on it)! We couldn’t believe our eyes! See the blurry video at long range below, where it is carrying a bone uphill. I couldn’t have dreamed up a better way to end the field season!

Phalarope females

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!

 

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 !