Slettnes: interesting but alarming results

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.

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Unravelling the mysteries of the Dotterel

The higher ridges and plateaus rising high above our study areas in Ammarnäs are home to an elusive bird: the Dotterel. Over the years, whilst working on Long-tailed Skuas and Red-necked Phalaropes, we have often heard Dotterels displaying and passing by from one ridge to another. Yet, our knowledge about their breeding ecology, habitat use and migration ecology is rather limited. Therefore, we have started a colour ringing project by which we hope to learn about their basic ecology such as habitat use, survival and site faithfulness.

Dotterels breed in low densities which makes it difficult to find a nest; over the years we have only incidentally found one. This year we have managed to find 8 nests! We find nests by following a male, which is the breeding sex, back to the nest. This may not seem difficult, but the bird’s plumage matches perfectly with their habitat which makes it almost impossible to locate a breeding individual, especially since they are only flushed when approached very closely. The trick is to search for a foraging male, and to stick with it when found! So far, we have caught seven males on the nest, using a walk-in-trap, for colour-ringing and sampling.

The males have proven to be very committed fathers. It amazes us that some males stay on the nest until we mildly push it off to measure the eggs and estimate the stage of incubation. The males behave very calm and often continue breeding as soon as we have finished our measurements as if nothing happened.

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On the other hand, female Dotterels are less committed to their brood and leave most of the breeding duties to the male. It is thought that females migrate further north after completing a clutch to do another breeding attempt. Surprising was our observation of a breeding female on the nest! Most females we encounter are in small groups of 2-6 birds. We have managed to catch some of these females using mist nets and tape lure. Let’s find out if we can get some ring recoveries in future seasons, possibly further north…

The 2018 field season is almost at an end. A few days are left to check Dotterel nests, ring chicks and explore some ridges before we migrate back south.

Morrison Pot

Fox caught red-handed / 27 years old male Arctic Skua / Logger retrieved of a tough phalarope

Lots of news to report from Slettnes! We are enjoying much activity at sea, where huge feeding frenzies of gulls (mostly Black-legged Kittiwakes and Herring Gulls) feast on pelagic fish together with Minke Whales and occasionally joined by White-beaked Dolphins, Humpbacks and Fin Whales. Many skuas (including migrating Pomarine and Long-tailed Skuas, plus the locally breeding Arctic Skuas) join the party as well. The Arctic Skuas seem to do very well in obtaining food.

Fox caught red-handed

On land however, things are not going that great for the Arctic Skuas. As reported before, most freshly laid clutches disappear after one or two days. To find out who takes them, we deployed camera traps at skua nests. Although it seems that nests with cameras are less quickly predated as other ones, we managed to capture two Red Foxes in the act of taking skua eggs! See below…

27 years old male Arctic Skua

Yesterday, we captured a male with a somewhat worn metal ring and a ring number that clearly didn’t belong to the series we have used since 2014… It turns out this bird has been ringed on 3 July 1991 as a chick at Slettnes, by Karl-Birger Strann. Actually, it was amongst the very first Arctic Skuas ringed here by Karl-Birger. By coincidence, the next colour-ring on the string read ‘KB’!

Seabirds typically have a slow reproduction but can get pretty old. In fact, the oldest confirmed wild bird is a seabird – a Laysan Albatross of over 60 years called ‘Wisdom’. For Arctic Skuas, the longevity records for European birds lists a 31-year-old Finnish bird as the oldest known individual, with an Icelandic 26-year-old bird as a second. Hence, KB beats the Icelandic bird, and if it manages to survive some more years, maybe it will beat the Finnish as well? We’ll see…

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KB – 27 years old and still going strong! Paired to CW – a light morph female wintering in West Africa. We hope to find out where KB winters as well.

Logger retrieved of a tough phalarope male

When Slettnes finally experienced a day with calm weather last week, Hans and I went out ‘phalaroping’: catching Red-necked Phalaropes using a mistnet. We captured several birds, and were surprised to even capture a male carrying a geolocator! To our surprise, this bird already carried a geolocator during 2015-2016, and got a new one in 2016 that we now retrieved. After three years, it was finally released of its 1.0g logger!

Virtually all geolocators of Red-necked Phalaropes were retrieved one year after deployment, with a few after two or even three years. Two or more years of data from the same individual allows us to study the consistency of individuals in their movements. In Red-necked Phalaropes wintering in the Arabian Sea, this is especially interesting because this area is known for its high variability in where and when food is available. Most Red-necked Phalaropes seem to respond to this variability by moving a lot, except a few – including this bird… The question is: are these movements individual strategies repeated every year, or are they flexible responses to current conditions, changing from year to year?

Unfortunately, after two years the battery of these geolocators is empty, which made it impossible for us (but not for the manufacturer) to download its data. While we wait for this, please have a look at this video (in Dutch) in which we take off the logger and show the track of this individual from 2015-2016.

 

Another failed breeding year for the Long-tailed Skuas in Ammarnäs, despite good Lemming numbers!

In Ammarnäs the Dutch/German/Swedish crew have had their first week of fieldwork. Summer came early this year and most of the tundra snow cover has melted. The first rumours of lemming presence and territorial Long-tailed Skuas observed by others at the field station made us eager to get out in the field. We were accompanied by journalists from Radio Sveriges who were keen on learning more on the research that is done at Ammarnäs. Peter gave an excellent interview that was aired on national radio on Friday the 15th.

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Peter is explaining our projects to Jonatan Martinsson from Radio Sveriges.

However, a few moments after crossing the treeline for the first time in 2018 we saw that our worst case scenario had played out on the tundra. The pair of Long-tailed Skuas that traditionally breeds at the Geppejaure area had left their territory already. Two colleagues at the station had observed them showing aggressive territorial behaviour just 3 days earlier.

After entering the Raurejaure area and exploring some good skua spots we had to draw a most disappointing conclusion: it’s going to be yet another non-breeding year, again! This is the third non-breeding year in a row… The strange thing is: up at the tundra Lemmings are present. We found quite some winter nests and corridors, which betrays their presence, and Tim and Noel even caught one alive! We also observed other raptors that may rely on Lemmings, such as Rough-legged Buzzard, several Short-eared Owls, and Hen Harrier on the tundra, and breeding Tengmalm’s Owl is present in the village. However, number of waders are low which could indicate high predation pressure. We were surprised to find one skua nest with a single egg that was already hatching. This means an extremely early start from this pair, and possibly also most other pairs that have tried but already failed. The day after we could at least see the first Long-tailed Skua chick for most of us who have only been in Ammarnäs in non-lemming years. However, on Björkfjället a large flock of 77 Long-tailed Skuas is already present, which indicates that most individuals have given up their breeding attempts and will soon be out to sea.

On the bright sight, we have more time to spend on our new Dotterel project! We have seen several individuals displaying and found our first territorial birds up at Gájsátje, the mountain that we have nicknamed ‘Miracle Mountain’. First catching attempts failed, as a territorial female escaped from our net, but looked promising! Tomorrow we will continue exploring Björkfjället and try to find nests of Dunlin and Dotterel.

Morrison Pot & Tim van der Meer

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)

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