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Theme 1 - North Atlantic Breeding Seabird Populations in Britain: Focus on Scotland

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Theme 1 - North Atlantic Breeding Seabird Populations in Britain: Focus on Scotland

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My BioArea looks at the coastline and islands of Scotland, examining their importance as breeding sites for internationally important populations of seabirds.
The cliff shown below is known as Noup Head, and is a major seabird nesting site in the Orkney Isles.

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Theme 1 - Britain's Breeding Seabirds: Global Importance

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Theme 1 - Britain's Breeding Seabirds: Global Importance

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The British Isles are one of the richest areas in the world for seabirds, and populations here are an important component of global biodiversity. Just under 8 million seabirds from 25 species breed in Britain and Ireland, including 90% of the world's Manx Shearwaters, 68% of Northern Gannets and 60% of Great Skuas.  This compares strongly with other major seabird centres: Falkland Islands (over 4 million, 22 species), Barents Sea (13 million, 25 species), New Zealand (20 million, 55 species).

Seabird populations in Britain benefit from: 1) an extensive coastline with varied nesting habitats (high cliffs, offshore islands, dunes and shingle beaches); 2) a diverse highly productive marine environment, rich in zooplankton and fish; 3) a ready food supply in the form of fisheries waste and discards; 4) minimal human exploitation of seabirds and their eggs.
This is an offshore Gannet colony at Hermaness, Shetland, with Great Skua in foreground.

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Theme 1 - Protection of Seabird Colonies

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Theme 1 - Protection of Seabird Colonies

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The conservation of seabird colonies is aided through a network of designated sites - Special Protection Areas (SPAs), notified under the EU Birds Directive (1979) to protect rare, vulnerable and migratory birds. The distribution of all existing and proposed SPAs in Britain is shown on the map here, with Scotland highlighted.  The Birds Directive states that conservation measures should be taken in both the land and sea areas, and so bird nesting areas have been supplemented by Marine SPAs to protect and manage sea areas that these birds use for feeding, wintering or migration.

In Scotland, there are 50 SPAs which have seabirds listed as a feature of interest.The map shows these sites are widespread around the coast. Some of the largest seabird colonies are found on the Northern Isles (Orkney and Shetland).

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Theme 1 - Seabirds in the Marine Ecosystem

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Theme 1 - Seabirds in the Marine Ecosystem

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Seabirds are species of bird that depend wholly or mainly on the marine environment for their survival. They spend the majority of their lives at sea, feeding at its surface or at varying depths in the water column.

Most of these species come ashore only to breed, and often return to the same sites year after year . So, the continued health and productivity of the seas around Scottish nesting sites is critical for these birds - the survival of chicks, and long-term population size, depends on sustainable supplies of fish and marine invertebrates.
Puffins at their nesting grounds in Shetland.

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The size of seabird colonies has been systematically monitored by governmental conservation projects throughout Britain since the 1980s. This allows population trends to be analysed annually, and identifies research needed to explore causes of declines in breeding populations.

In Scotland, nine of the commonest seabirds species have shown sustained declines over the past 20 years. The reasons for the declines are complex and may be a result of changes in fishing effort (resulting in changes to food availability), climate change (altering prey distributions and resulting in mortality of some species due to extreme weather events) and the effects of non-native species (such as rats on islands).

One species badly affected has been the Black-legged Kittiwake, a small species of gull which feeds on small shoaling fish such as sandeels. Since the 1990s Kittiwakes' abundance has dropped steeply in Scotland, and Orkney and Shetland have seen complete colony failures as birds have struggled to find sufficient food for their chicks. There is evidence that sandeel stocks have been depressed by warming ocean currents, exacerbated by over-fishing.

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Theme 2 - Species with Predator/Prey Relationships

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Theme 2 - Species with Predator/Prey Relationships

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1. Atlantic Puffin - Lesser Sandeel.  Sandeels are small (<20cm), energy-rich shoaling fish which are favoured prey of the Atlantic Puffin - photo below. Sandeels occur in shallow inshore waters over sandy seabeds, and historically have been an abundant and important component of food webs in the North Atlantic. In summer, Puffins breeding around Scotland make foraging flights from their island nesting colonies to shallow coasts to hunt sandeels.
2. Great Black-Backed Gull - Puffin.
These gulls are the largest breeding gull in Scotland. Their diet is varied, including rabbits, other seabirds, and a range of fish. The Northern Isles are one of their key breeding areas in the UK. To evade predators, Puffins make their nests in burrows in soil on cliff-tops, but adults are vulnerable to gull attacks particularly as they return to their burrows with fish.

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Niche partitioning is an interesting concept when looking at seabird feeding strategies. The fish and marine fauna of the North Atlantic generally provide an abundant food supply for seabird populations, but with many birds hunting the same prey species (e.g. small shoaling fish such as sandeels), how might direct competition at feeding grounds be mitigated? One answer might be foraging behaviour - we know that some birds are surface feeders while other are depth feeders (see table). Puffins 'duck dive' from the sea surface and chase prey, using their wings like flippers; they can dive as deep as 60m, although the average is 20m. By contrast, Common and Arctic Terns make 'plunge dives' to take prey that are just below the water surface (top 0.5m). So some birds exploit prey at different depths in the water column, and the length of foraging flights - whether birds feed inshore, close to the coast, or go further offshore to reach pelagic feeding grounds - may be important too in niche partitioning.

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Simplified trophic pyramid for marine ecocsystem, North Atlantic Sea

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1. Arctic Skua and other seabirds
Arctic Skuas are small, gull-like seabirds, and their foraging habits include actions known as 'kleptoparasitism'. This involves taking fish catches from other smaller seabird species such as Kittiwakes, terns and auks, by pursuit and attack in flight until the smaller birds drop their prey.  (This is not perhaps a formal 'host-parasite' relationship where one organism lives in or on another, but it does involve one organism taking resources from another). The photo shows an Arctic Skua chasing a tern for its fish prey.
2. European Shag and nematode worms
Shags feed on small fish, which are a source of infection of larvae of nematode worms.  Larval worms moult to become sexually mature adults which attach to the lining of birds' intestines and lower oesophagus. The parasite load can affect Shags' ability to fly when feeding.

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Little tern diving for fish at water surface

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Puffin swimming underwater

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Theme 2 - Ecological Niche of Two Animals

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Theme 2 - Ecological Niche of Two Animals

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To explore the niches of two organisms in my BioArea I will explain some key aspects of their habits and ecology - breeding and habitats, diet, seasonal activity patterns, position in food webs.
1. Lesser Sandeel, Ammodytes marinus, a species of small shoaling fish associated with shallow sandy inshore waters. Burrow in sandy sediments, emerging to feed close to burrows during daylight, April-September. Food includes zooplankton and fish larvae (a 1st-level consumer in the marine trophic web). Inactive during Sept-March except to spawn Dec-January, when aged 1-3 years and depending on geographic location. Sandeels are a major prey for marine predators, both fish and seabirds.
2. Common Guillemot, Uria aalge,
a species of auk, breeding on coastal cliffs around Scotland. Social breeder, nests in large, densely packed colonies on cliff faces (safe from mammalian predators) - photo below. Does not build nest, lays single large egg on bare rock / ledge. Feeds at sea, swimming below surface to catch mainly sandeels, sprats and other small fish (a 3rd level consumer in the marine trophic web). Nesting period in GB is March-July, leaving colonies in July-August when adults moult and are flightless. GB birds disperse and migrate throughout the NE Atlantic and North Sea in autumn/winter.

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Theme 3 - Habitat Loss, Fragmentation, Degradation

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Theme 3 - Habitat Loss, Fragmentation, Degradation

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Seabird populations rise and decline in response to marine habitat health. They make especially good indicators of changes taking place in marine ecosystems because they are high up the food web, long-lived, and conspicuous during the breeding season. Many environmental changes are human-induced, affecting marine food chains, or causing direct damage to birds individually or their nesting areas. The table here summarises pressures facing seabirds in Britain.

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Climate change is believed to be one of the primary causes of the decline in Scotland's seabird populations seen over the past 25 years, with evidence pointing to the effect of warming seas on marine food chains, and in turn on adult bird survival and breeding success.
Average winter sea surface temperatures (SST) in the North Sea have increased by around 1oC since the early 1980s (see graph below ). Sea temperature rise has led to a change in species composition and biomass of the North Sea zooplankton community, in particular a decline in copepods which are a major food source for the lesser sandeel - a key prey item for seabirds.
In the North Atlantic, decreased survival in both the Kittiwake and Puffin has been demonstrated with increasing SST. There is regional variation in such effects, but they seem especially evident in seas around Shetland, where climate warming effects are being overlain on the natural background oscillations of ocean currents which are presently in a warming phase. The later age of sandeel spawning (see Theme 3, Wildlife Exploitation), combined with past unregulated fishing of sandeels, also likely caused food scarcity and knock-on breeding failure in Shetland Puffins and Kittiwakes in recent decades.
Other detrimental impacts of climate warming on seabird breeding include:

mismatches between times of plankton blooms, prey abundance and bird breeding seasons - can lead to poor chick growth, shortened nesting periods and lower fledging success.

predicted increase in the frequency of extreme weather events - storms at sea can prevent adequate feeding, and severe weather at nest sites can cause mass mortality of chicks.

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Theme 3 - Habitat Change & Seabird Numbers

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Theme 3 - Habitat Change & Seabird Numbers

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Monitoring of seabirds from 1986-2016 in Scotland has looked at annual numbers of each species coming to their nesting sites, and at the breeding success of each species - i.e. the number of chicks produced each year.

Of 24 seabird species that bred in Scotland, 12 show trends of declining breeding numbers and breeding success. Between 1986 and 2011, after peaking in 1991, these species' average numbers declined steadily, falling to 50% below the 1986 level. Since 2011 there has been a slight recovery and in 2016 breeding numbers were 38% below the 1986 level. See graphs below.

Decline in bird numbers 1986-2011 was greatest for:

Arctic Skua (-77%)

Arctic Tern (-72%)

Kittiwake (-66%)

Herring Gull (-58%)

European Shag (-47%)

There is significant geographic variation in seabird numbers and breeding success over Scotland, with the Northern Isles - Orkney and Shetland - seeing the most serious declines. Likely relationships between habitat changes and bird populations are discussed in other Theme 3 boxes.

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Industrial sandeel fisheries around the Scottish coast have existed since the 1970s, with the fish being used in animal feed and fertiliser. Concern of over-exploitation of sandeel stocks was raised in the late 1980s as declines in breeding seabirds dependent on sandeel, such as Kittiwake and Tern species, were observed, especially around northernmost coasts and islands.
It is thought these birds are most vulnerable to reductions in pelagic fish stocks because they are small surface-feeding species, with specialised and energetically intensive feeding methods.

Research shows that sandeel stocks around Shetland and SE Scotland are vulnerable to decline because of oceanographic changes combined with their naturally slower growth rates (spawning at 3 years old) , and so in these areas sandeel fishing was limiting seabird survival and breeding. To try and address this, sandeel fishing off north-eastern Scotland has been banned since 2000 and the Shetland fishery has been scaled down.

But reducing sandeel fishing is not a simple 'cause and effect' solution to restoring seabird survival. A major factor influencing sandeel numbers is populations of fish predators, which compete with the birds - mackerel have boomed in the North Atlantic in recent years and their impact on sandeel stocks is probably greater than sandeel fishing. Also, legal requirements to reduce discard and by-catch from boats in North Sea fisheries has removed a major food source for scavenging birds such as Great Skuas and Great Black-backed Gulls, which now predate smaller seabirds more often at their nesting sites.

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Theme 3 - Conservation Status of Seabird Species

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Theme 3 - Conservation Status of Seabird Species

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On the IUCN Red List, one species, the Puffin, is classified as Vulnerable. The UK supports c.10% of the world Puffin population.
Other seabirds of Scotland's coasts have a IUCN 'Least Concern' status.
When looking at the 2015 UK assessment of 'Birds of Conservation Concern' (BoCC), several are identified as Red List and Amber List species.

BoCC Red List = species showing Severe declines. Examples: Arctic Skua, Herring Gull, European Shag, Puffin

BoCC Amber List = species showing Moderate declines. Examples: Arctic Tern, Guillemot, Fulmar

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Seabird breeding sites on Scottish islands are vulnerable to predation by non-native mammals. Brown and black rats and American mink are key problem species, taking eggs, chicks and sometimes adult birds. There are records of local extinctions of some colonies of ground-nesting seabirds such as terns, gulls, Storm-Petrels, Manx Shearwater and Atlantic Puffin. Ailsa Craig, an island off the Scottish NW coast supported 250,000 pairs of Puffins in the 1860s, but by the end of the 19th century brown rats had colonised and in 50 years Puffins were extinct as a breeding bird here. Successful rat eradication took place 1989-90, and Puffin are recolonising, but slowly - 130 pairs bred there in 2018.
The Shiant Isles in the Hebrides are a different case, where extermination of c.3,500 black rats recently took place in order to protect existing, nationally important colonies of Puffins (10% of of UK population) and Razorbills (7% of UK population). Poison bait traps were laid in 2014, and monitoring shows that no rats were present 2016-18. It's hoped that bird breeding success will increase with rat-free conditions, and also restore safe nesting conditions for Manx Shearwaters and Storm Petrels, which used to breed here before the arrival of rats in 19th century. Strict biosecurity measures for visiting boats are operated now, to ensure recolonisation by rats does not occur.

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Theme 3 - Cultural Response to Seabird Losses

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Theme 3 - Cultural Response to Seabird Losses

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The huge scale of seabird declines in northern Scotland has dismayed conservationists, islanders and naturalists. The loss of whole colonies of Puffins, Kittiwakes and Terns has made headlines in national and local newspapers. There is a particular sadness for those who visited the cliffs and islands in earlier years, to experience the spectacular noise, smells and sights of 'bird cities' clinging to the rocks in the wild sea, to find that now there is emptiness and silence at those coasts.
But, as local newspapers in Shetland say, although smaller in size the seabird colonies here are still good for visitors to see, and tourists can help support conservationists' case to protect the marine environment.

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Theme 3 - Cultural Response to Seabird Losses

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Theme 3 - Cultural Response to Seabird Losses

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The Shiant Isles are important in Europe for their numbers of breeding seabirds - 62,000 Puffins, 9,000 Guillemots, 8,000 Razorbills. The islands are owned by naturalist and author Adam Nicholson, who has written with great sympathy of his bond with the three islands, and his responsibility to help ensure that the birds return each summer to take their ownership of the coasts and cliffs and fields. I recommend reading his books and viewing two programmes he has made.

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Theme 3 - Cultural Response to Seabird Losses

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Theme 3 - Cultural Response to Seabird Losses

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"The Last Seabird Summer?", Part 1. TV programme with Adam Nicholson (2016)

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BC - The Last Seabird Summer? Series 1 (2016) - Part 1: Living With The Birds

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BBC - The Last Seabird Summer? Series 1 (2016) Series following Adam Nicolson and the seabirds of the Shiants, a small cluster of Scottish islands. With crisis threatening their future, Adam traces the history of our relationship with seabirds.

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What you hear when standing near a cliff with half a million breeding seabirds -  guillemots, kittiwakes, fulmars, gannets and gulls . To complete the experience imagine the smell of guano and the air full of wings!

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Above the pounding of waves at the foot of the cliffs, a cacophony of the seabirds colony: Guillemots, Kittiwake, Fulmars, Gannets and gulls. Light rain starts to fall. Recorded at Bempton Cliffs, North Yorkshire by Richard Margoschis.

British Library Reference:  1CD0091587 CD1 BD5

Image Reference: https://pixabay.com/en/cliffs-rock-water-nature-coast-404051/

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Theme 3 - Cultural Response to Seabird Losses

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Theme 3 - Cultural Response to Seabird Losses

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"The Last Seabird Summer?", Part 2. TV programme with Adam Nicholson (2016)

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BBC - The Last Seabird Summer? Series 1 (2016) - Part 2: Trouble at Sea

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BBC - The Last Seabird Summer? Series 1 (2016) Series following Adam Nicolson and the seabirds of the Shiants, a small cluster of Scottish islands. With crisis threatening their future, Adam traces the history of our relationship with seabirds.