BTO - British Trust for Ornithology - Scotland

The astonishing migration of Scotland’s Arctic Skuas

WEBSITEEDITOR — Fri, 13 Oct 2023 11:21:47 +0000

BTO Senior Research Ecologist Nina O’Hanlon explores the fascinating findings of the Arctic Skua tracking project. Yes

Senior Research Ecologist

Nina is a Senior Research Ecologist and part of the Wetland and Marine Research Team, based within BTO Scotland. Her role involves reporting, analysis and fieldwork with a focus on marine birds.

There’s something exhilarating about the aerobatic display that ensues as the skua pursues its chosen victim, both birds twisting and turning high in the sky and back down to the sea, until finally, the Kittiwake regurgitates its last meal or the Arctic Skua gives up and finds a new and unsuspecting target.

Migratory pirates

Skuas are often called the pirates of the sea, a name which is well-deserved: powerful and agile, they chase and harass other seabirds, stealing much of their food instead of catching their own – a behaviour known as kleptoparasitism. In North America, Arctic Skuas are even called Parasitic Jaegers due to their habit of pursuing species such as auks, gulls and terns and forcing them to drop their food.

With the populations of many of our seabird species falling, it is not surprising that Arctic Skuas – which depend largely on these other birds for food – have also experienced severe declines. The UK breeding population, restricted to north and west Scotland, declined by 70% between 2000 and 2019! And these declines have not just occurred in Scotland. Arctic Skuas are also struggling in other parts of northern Europe including the Faeroes, Iceland and Norway.

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Arctic Skuas are piratical and source most of their food by harassing other birds, like this Kittiwake, forcing them to drop their latest catch or even to regurgitate their last meal. This Arctic Skua has ‘pale phase’ plumage.

The UK breeding population of Arctic Skuas has declined by 70% between 2000 and 2019, a trend that is reflected in other parts of northern Europe including the Faeroes, Iceland and Norway.

These declines are thought to be due to poor food availability during the breeding season, which has caused declines in the seabirds the skuas steal from and therefore reduced the food available for the skuas. A lack of food means the skuas can’t provide for their chicks, so fewer young birds survive to fledge each year. This is exacerbated in some colonies by predation of chicks by the larger Great Skua, which increases in years where this species’ alternative fish prey is limited. Low food supplies may also have implications for the health and survival rates of the adult birds themselves.

To fully understand what is causing Arctic Skua declines, and to identify effective conservation actions, we need to understand where the skuas are distributed during the winter months.

Arctic Skuas are long-distance migratory seabirds, and spend only around a third of the year at the breeding colony: after raising their young, they leave their northern colonies to spend their non-breeding season in warmer, more productive waters in the southern hemisphere. Therefore, to fully understand what is causing the large declines in Arctic Skuas, and to help identify effective conservation actions, we need to understand where the skuas are distributed during the rest of the year, during the northern hemisphere’s winter months.

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One of the Fair Isle Arctic Skuas showing how the deployed geolocator is attached to the orange alpha-numeric engraved colour ring. This skua has ‘dark phase’ plumage. The inset shows a close-up of a colour ring and geolocator.

Tracking revelations

Recent advances in technology have allowed scientists to develop tiny tracking devices which are light enough to attach to birds, and enable us to follow their movements for potentially thousands of miles.

At BTO, we wanted to shed light on the migration routes and wintering areas of the Arctic Skuas breeding in Scotland. To do this, we decided to attach geolocators to adult Arctic Skuas breeding on Fair Isle, Shetland, and Rousay, Orkney, in 2017 and 2018.

These small tracking devices weigh less than 1 g and are attached to a plastic colour ring, which is engraved with a unique code and placed on each bird’s right leg. Each bird is identifiable by the code on its ring – for example, AAA, AAH, AAJ and so on.

Each skua’s movements are saved to the geolocators themselves, so we needed to recapture the skuas to remove the tracking devices and download the all-important data.

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Sarah Harris (left) and John Calladine (right) from BTO tagging an Arctic Skua on Fair Isle.

Each skua’s movements are saved to the geolocators themselves, which means that we needed to recapture the skuas to remove the tracking devices and download the all-important data. Thanks to a lot of dedicated effort in subsequent years, six devices were retrieved from Fair Isle and four from Rousay.

So where did the Scottish Arctic Skuas go?

During our autumn, most individuals from both the Fair Isle and Rousay colonies migrated south after the breeding season, moving through the North Sea and the English Channel then along the Iberian Peninsula and off West Africa. However, in both years it was tracked, skua AAU from Rousay headed west instead, then migrated southwards over the Atlantic before heading south-east to the coast of Portugal.

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Southbound (autumn) and northbound (spring) migration routes of the tracked Arctic Skuas from Fair Isle (2017–19) and Rousay (2018–20). The colours and three-letter codes correspond to individual birds. The triangle shows the location of the breeding colonies in Scotland. The break in the journey lines is caused by the researchers removing data from the geolocators from around the spring and autumn equinoxes. The geolocators use the timing of sunrise and sunset to estimate their position across the globe, but day length is the same globally around the equinoxes – this means that the geolocators cannot estimate their location accurately during this period.

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Circles show the midwinter locations of each tracked Arctic Skua from Fair Isle and Rousay in the Canary Current (off West Africa), Benguela Current (south-west Africa) and Patagonian Shelf (off eastern South America). Wintering locations of the birds with two years of data (AAA and AAN from Fair Isle, and AAU and AHN from Rousay) were virtually the same each year. The triangle shows the location of the breeding colonies in Scotland.

Amazingly, given the relatively small number of birds that we tracked, we saw that skuas from the same colony wintered across the whole range of the Atlantic Ocean. AAU and two other birds from Fair Isle wintered around the Canary Current off West Africa, whilst the remaining individuals continued south and then either headed west to winter around the Patagonian Shelf, or east to the Benguela Current – covering distances over 10,000 km! Although existing ringing data has suggested that Arctic Skuas breeding in Scotland winter off West and southern Africa, our tracking study was the first time they have been shown to winter off South America.

Existing ringing data has suggested that Arctic Skuas breeding in Scotland winter off West and southern Africa, but our tracking study was the first time they have been shown to winter off South America.

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The Arctic Skua tracking study revealed the mid-Atlantic to be an important feeding and resting area for the skuas on their northbound migration.

In spring, individuals that wintered around the Patagonian Shelf and Benguela Current returned north, mainly via West Africa. However, unlike in autumn, all individuals, including those wintering in the Canary Current, headed into the mid-Atlantic before returning to Scotland. This revealed that the mid-Atlantic is an important staging area (like a favourite motorway service station) for Arctic Skuas during their northbound migration, where they feed up to get in good body condition before the breeding season. This mid-Atlantic area is a region of high marine productivity, and therefore high food availability. Part of the region was recently designated as a Marine Protected Area due to its importance for numerous seabird species including Kittiwakes, Arctic Terns and Puffins.

Our study revealed that the mid-Atlantic Ocean is an important staging area for Arctic Skuas, where they feed up to get in good body condition before the breeding season.

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The main staging areas of Fair Isle and Rousay Arctic Skuas during southbound autumn migration (orange) and northbound spring migration (green), with core wintering distributions shown in purple. Staging areas are locations where birds typically paused their journey to rest or feed. Letters refer to the three wintering areas: CC – Canary Current; BC – Benguela Current; and PS – Patagonian Shelf. Geolocator data from the skua ACL from Rousay showed the bird did winter off the Patagonian Shelf but there were not enough data to produce a robust representation on the maps.

The wider picture

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Researchers have also been tracking Arctic Skuas breeding in the Faeroes, Norway and Svalbard. This pair was photographed in the Varangerfjord, in north-east Norway. The different plumages are called ‘phases’ or ‘morphs’; Arctic Skuas are known for occurring in both a dark phase (the bird on the left) and a pale phase (the bird on the right).

Whilst we were tracking Arctic Skuas in Scotland, researchers in the Faeroes, Norway and Svalbard were doing the same. A total of 129 Arctic Skuas have been tracked across these four populations since 2009, with many individuals, including four from Scotland, being tracked for multiple years. In nearly every case, skuas with multiple years of data wintered in the same areas and followed similar migratory routes each year.

As we saw in Scotland, skuas from the same breeding population migrated to different wintering areas across the entire Atlantic Ocean. Most individuals from these more northerly populations spent time in the mid-Atlantic Ocean to feed up during both autumn and spring migrations, further highlighting how important this area is for migrating Arctic Skuas.

By tracking Arctic Skuas from multiple populations, we can also explore whether differences and similarities in migratory routes, staging areas and wintering areas are reflected in differences in population trends. For example, Arctic Skuas are declining in Svalbard to a lesser extent than they are in Scotland, the Faeroes and Norway. Most skuas from Svalbard didn’t winter as far south as those from the other populations, and they tended to stage further west in the mid-North Atlantic during migration. This could indicate that the Svalbard skuas are finding more food or are encountering fewer threats in these areas, compared to the staging areas used by the other populations.

The impact of our research

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Skuas that migrate south through the North Sea, including those from Scotland, might be vulnerable to increased collision risk with offshore wind farms.

Now we have a better understanding of where Arctic Skuas are distributed outside the breeding season, we can start to explore which threats they might encounter during migration and in what we refer to as their wintering areas (although, of course, it is summer in the southern hemisphere when the skuas are there).

For example, individuals migrating south through the North Sea, including those from Scotland, might be vulnerable to increased collision risk with offshore wind farms.

By tracking Arctic Skuas from multiple populations, we can start to explore whether differences and similarities in migratory routes, staging areas and wintering areas are reflected in differences in population trends.

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The study identified an area in the South Atlantic Ocean off the Namib Desert coastline as an important staging area for Arctic Skuas that breed in Scotland.

Knowledge of the birds’ non-breeding locations will also help us identify the most effective conservation actions for these birds. Although a large area of the mid-Atlantic has already been designated as a Marine Protected Area, the tracking data highlight an area off West Africa that is also important for staging and wintering Arctic Skuas. If this was also designated as a Marine Protected Area it would benefit a wide range of seabirds, not just the skuas – as it is not just Arctic Skuas that are in decline. Many long-distance migrant seabirds are declining globally, and their conservation is a challenge: they depend on productive marine conditions over large ocean regions, and are likely to encounter a range of threats along their extensive migratory routes.

International collaborations, a key focus of World Migratory Bird Day, are therefore essential to conserve migrant seabirds such as Arctic Skuas, and allow us to continue to enjoy them, whether at their breeding colonies or passing by on an autumn seawatch.

Special thanks to the amazing BTO fieldwork team of Sarah Harris and John Calladine, the fantastic Helen and David Aiton on Rousay, and everyone who helped with fieldwork as well as all landowners, including Fair Isle Bird Observatory and NatureScot who provided in-the-field-support in Scotland. Thanks also to the rest of the BTO project team – Chris Thaxter, Greg Conway, Dawn Balmer and Liz Humphreys – and to Rob van Bemmelen and Katherine Snell.

Since the Arctic Skua research programme was established in 2017, BTO donors have donated more than £225,000 to fund the work. We are enormously grateful for this very generous support from a small number of committed individuals. The research could not have been delivered without this funding.

World Migratory Bird Day 2023

This blog post was created to celebrate World Migratory Bird Day (WMBD) 2023, a global event which increases the level of awareness about the threats that migratory birds are facing.

The theme of WMBD 2023 is Water, which highlights the importance of this resource for migrating birds – including for species like the Arctic Skua, which spends most of its life at sea and migrates thousands of kilometres over the ocean and across both hemispheres every year.

BTO’s Arctic Skua tracking project aims to understand where these birds spend their time when they’re not at their breeding colonies, so we can better inform global efforts to protect this species.

Tracking Rousay’s Arctic Skuas was made possible by the dedication and skill of the fieldworkers behind the project. Read more in our other blog for WMBD 2023, written by skua experts Helen and David Aiton.

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Volunteer for the Seabird Monitoring Programme

Alongside our tracking projects, we carry out long-term population monitoring of the internationally important breeding seabird colonies in the UK. Together, data from these projects help us understand their declines and drive positive change.

If you would like to help us monitor seabirds like the Arctic Skua, visit the Seabird Monitoring Programme pages to look for vacant survey sites near you.

Look for survey sites

On World Migratory Bird Day, BTO Senior Research Ecologist Nina O’Hanlon explores the fascinating findings of the Arctic Skua tracking project.

1 October 2023

Picture the scene: a flock of Kittiwakes, casually dip-feeding and floating around on a calm sea. Then, suddenly, havoc arises as a dark shape zips into view – an elegant but formidable seabird – an Arctic Skua.

BTO Scotland

13 Oct 2023

Scotland

BirdTrack migration blog (15–21 September)

SCMAYSON — Fri, 15 Sep 2023 08:37:38 +0000

Now we are moving into mid September, BirdTrack reporting rates have increased for many passage migrants and winter visitors. This is especially true for several duck and wader species, which come to estuaries and wetlands across Britain and Ireland to feed up in large numbers.

Nina O’Hanlon

Senior Research Ecologist

Nina is a Senior Research Ecologist and part of the Wetland and Marine Research Team, based within BTO Scotland. Her role involves reporting, analysis and fieldwork with a focus on marine birds.

BirdTrack

Look out for the smaller Little Stints in amongst flocks of Dunlin. These small waders pass through Britain and Ireland each autumn.

Arrivals of Snipe, Dunlin and Curlew Sandpiper have noticeably increased recently, with the peak passage of Curlew Sandpipers likely to occur over the next week. Wigeon, Teal, Pintail and Shoveler also saw an increase in reporting rates which will continue over the next month, with birds moving south from their widely dispersed breeding grounds, from Iceland and Fennoscandia to Russia. Skeins of Pink-footed Geese continued to arrive adding to the autumnal feel despite the unseasonably high temperatures across much of the country last weekend. Seabirds also continue to feature, with reports of Leach’s Petrels beginning to increase.

As with last week, Meadow Pipits continue to be well recorded with clear skies in many areas over the weekend providing good visible migration opportunities. Reports of Chiffchaffs are also starting to increase, as mid to late September is the peak time for autumn passage of birds moving south from Fennoscandia. Keep an ear out for their “hweet” call.

Rarity highlights from the past week include a stunning American Yellow Warbler on Foula, Shetland – as bright as its name suggests – whilst a Sharp-tailed Sandpiper (an eastern Siberian breeder) was found at Montrose Basin in Angus. The Red-footed Booby remains off Scilly, and a Brown Booby has also been frequenting several buoys off Cleveland.

The silvery underwings of Sooty Shearwater are a good identification feature and can be seen even at long range.

Looking ahead

High pressure is set to build over the weekend with some dry, sunny spells and relatively light winds before heavy rain and thunderstorms are expected on Sunday, moving up from the south. Into next week, a period of low pressure will bring heavy rain and strong westerly winds – not the most favourable conditions for migration.

However, more waders are expected with arrivals of Dunlin set to continue along with Bar-tailed Godwits, Knot and Little Stints. The peak autumn passage of these latter three species typically occurs in mid September. A high proportion of birds found will be juveniles, which generally migrate later than adults. Juvenile waders tend to stop to feed up more regularly than adults, as older birds can make longer, non-stop, migratory journeys.

Internationally important numbers of Knot and Bar-tailed Godwits will stay and winter in estuaries around Britain and Ireland. However, Little Stints are largely passage migrants. These miniature waders only stop here briefly during their long southbound migrations between their breeding areas in Siberia and wintering grounds in Africa, with some individuals migrating over 12,000 km! Given that most will be juveniles, the number of autumn passage Little Stints not only depends on the weather but also on the year’s breeding success. This weekend marks the start of the winter priority period for the Wetland Bird Survey (WeBS), with Sunday being the core count date, so do keep an eye out for these waders while you take part.

Seawatching should continue to be fruitful, with this week typically being the peak passage time for Sooty Shearwaters. These elegant seabirds are all dark with silvery flashes on the underside of their long stiff wings. They have a powerful flight, and in high winds glide characteristically in high arcs over the waves. Mid September is also a good time for passage Arctic and Long-tailed Skuas – equally elegant seabirds that are a joy to watch.

1 September 2023

Snipe, by David Scott / BTO

Wetland and Marine Research Team

Surveys Team

BTO Scotland

15 Sep 2023

BirdTrack Migration

A BTO Bird Camp bonanza

WEBSITEEDITOR — Thu, 24 Aug 2023 11:31:41 +0000

Following a great summer of Bird Camps, our campers, Youth volunteers and BTO staff share their experiences and thanks with the wider public.

Bird Camp staff, volunteers and campers

SOC/BTO Scottish Bird Camp

Buoyed by the success of the first-ever Scottish Bird Camp in 2022, the Scottish Ornithologists’ Club (SOC) and BTO were excited to launch Bird Camp 2023, which took place over the weekend of 26–28 May.

Once again, we based the camp in East Lothian, and campers began to arrive late on Friday afternoon – all tooled up with binoculars, scopes and cameras (so many cameras!) – to get settled into the accommodation.

Perhaps miraculously, we enjoyed superb weather for the whole weekend and all the planned activities could go ahead! It was an action-packed weekend which included moth trapping, arts and crafts, nest monitoring, a boat trip to Bass Rock, building bird boxes, a ringing demonstration and a nature walk at the coast.

Our huge thanks go to the group of amazing young people who joined us for the weekend. They did everything with great enthusiasm and were always keen to learn more. They were great company and we’re sure we’ll be seeing them again in the future!

Thanks also to all our volunteer leaders, and everyone who helped make it such a special weekend.

Steve Willis – Scottish Bird Camp lead for BTO Scotland

Read more about the SOC/BTO Bird Camp 2023 on the SOC Blog.

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The SOC/BTO Bird Camp was made possible by the generous support of our funders:

The family of Ronald Guild - teacher, environmental activist, lifelong lover of nature and of all things East Lothian
The Cameron Bespolka Trust
The British Birds Charitable Trust
Anonymous SOC Lothian Branch members

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Bird Camp Wales

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On 16–18 June, I attended BTO Bird Camp Wales for the second year in a row, in Pembrokeshire. There were a lot of old faces and friends there, but also some new people who came. It was lovely to see everyone again in person because I have only been in contact via WhatsApp since last year. My friends at school don’t have the same interests as me so I love bird camp because it lets me make friends with people who do.

I loved every minute of bird camp but here are my favourite bits:

The places: Some of these are amazing! We went to places like Skomer Island and Stack Rocks. At these places, we saw some of the star species like Puffins, Guillemots, Peregrines and Manx Shearwaters.

The food: There was lovely food back at camp that the volunteers had made for dinner and lunch. My favourite food was the chilli on the first night there.

I loved bird camp with all my heart and hope to go again next year. Thank you to all the staff for making it a blast for me and everyone else.

The staff: The volunteers working with us were beyond wonderful and I learnt so much from them. I hope to work with them in the future again. Faye and Chris (BTO Youth staff) who ran the camp were as wonderful as the volunteers and I hope to meet them again next year.

I would talk about the bad bits of bird camp – but there are none! I loved bird camp with all my heart and hope to go again next year. Thank you to all the staff for making it a blast for me and everyone else.

Henry (12) – Bird Camp Wales camper

Read more about Bird Camp Wales 2023 >

Bird Camp England

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Summarising the Bird Camp experience is as difficult as resisting the temptation to raise your binoculars when you’re there. I had an incredible experience as a camper in 2022, and this was mirrored for me in 2023, when I found myself on the other side of the experience as a youth volunteer. I loved seeing lifelong memories being made and new friendships forming, just as I had experienced the year prior.

We had fifteen enthusiastic and knowledgeable campers who each had their own creative flair. I particularly enjoyed seeing the campers working on exhibition pieces for parents and guardians to see at the end of the weekend. These included paintings of habitats, nature journalling, and even acrostic poems! Our base of operations was the classroom at Flatford Mill in Suffolk where exhibition pieces (and sightings lists!) were worked on between wildlife-watching trips.

One of the many highlights of the weekend was the boat trip from Harwich Harbour. The coastal air added Little Terns, Cormorants, seals and more to the sightings lists, following on from the day before, which included the excitement of seeing Turtle Doves!

Seeing the fantastic young people all having a blast reminded me of the importance of these camps. No matter your birding knowledge or confidence level, for those two nights, Bird Camp is your home.

As well as the boat trip, campers were given insights into how to contribute to BTO science – bird ringing and point count surveys – and taking part in moth trapping and pollinator surveys. And of course, the healthy competition of the bioblitz and relaxation from the mindfulness session brought campers closer together too.

I was hugely grateful for the England Bird Camp after I attended as a camper last year, for the way it opened up the world of birdwatching for me. This year, seeing the fantastic young people all having a blast reminded me of the importance of these camps. No matter your birding knowledge or confidence level, for those two nights, Bird Camp is your home.

Adam (16) – Bird Camp England 2023 Volunteer and Youth Advisory Panel Member

Read more about Bird Camp England 2023 >

Bird Camp Northern Ireland

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Where do I start? How about with the weather? I would say it rained for about 75% of the weekend. But despite this not once did I hear a young person complain. Instead, they put on their coats, grabbed their binoculars and marched out into the rain. This is the second year BTO has run a camp in Northern Ireland, and in both years I have been so inspired by the knowledge, curiosity and enthusiasm the young people have for the natural world and everything it brings.

For me, the highlights of this camp include the bioblitz in Davagh Forest, archery at Gortin Activity Centre and the bird ringing demonstration run by Stephen, Sorrel and Emma. After the disappointment of having no birds at last year’s ringing demonstration, it was amazing to catch 22 birds this year. The team was amazing and kept all the young people interested and getting to release a goldcrest is an experience I will never forget.

Bird Camp also happened to fall on my birthday this year. A 5:30 wake up, a titanic cake decoration, 14 young people singing happy birthday, and spending 3 hours in the rain sums up one of the stranger birthdays I’ve had, but I wouldn’t have had it any other way.

I have been so inspired by the knowledge, curiosity and enthusiasm the young people have for the natural world and everything it brings.

Each year, I’ve taken something different away from Bird Camp. Last year I learned never to treat a bird as if it’s boring. Doesn’t matter how common you think it is, to someone else it could be the most exciting bird they’ve seen all year.

This year, I learnt how to adapt to changing circumstances and be flexible and how to prepare for and run a session of my own. Most of all, I learned that there is no such thing as bad weather, just the wrong clothing. Oh, and I’m also apparently amazing at archery!

Benjamin – Bird Camp Northern Ireland 2023 volunteer, Youth Representative for Northern Ireland and Mental Health & Mindfulness (MMH) project participant

Read more about Bird Camp Northern Ireland 2023 >

BTO Bird Camps in England, Northern Ireland and Wales are made possible thanks to the support of the Cameron Bespolka Trust.

Young people are the future of BTO

With your help, we can reach more young people through events like Bird Camp.

Donate to the BTO Youth Appeal today

2 August 2023

Following a great summer of Bird Camps, our campers, Youth volunteers and BTO staff share their experiences and thanks with the wider public.

BTO Youth Appeal 24 Aug 2023