This week saw the publication of a new book entitled Seabirds Count – A census of breeding seabirds in Britain and Ireland (2015-2021). The book, co-produced by JNCC, RSPB, BirdWatch Ireland, the National Parks and Wildlife Service (Ireland), and published by Lynx Edicions, documents results from the fourth census of Britain and Ireland’s internationally important breeding seabirds. Today’s blog, by Dr Allan Perkins, Senior Conservation Scientist, gives a brief overview of what the book covers and why such censuses are important.
Assessing population change
Alongside an online resource (which will follow shortly), the book provides an updated assessment of seabird population sizes in Britain, Ireland, the Channel Islands and Isle of Man, and makes comparisons with previous census results spanning five decades.
Manx Shearwater adult in flight (c) Greg Morgan (rspb-images.com)
Seabirds Count covered all 25 of our regularly breeding seabird species, including nocturnal burrow-nesters such as Manx Shearwater as well as inland and urban-nesting gulls. Several rare species are also documented. The census provides the most complete picture we have of seabird population size and change since its predecessor, Seabird 2000, at the turn of the 21st century.
Although many seabird colonies are monitored regularly, such as at nature reserves, a large proportion are rarely visited, let alone surveyed. Some seabirds are also difficult to count, such as the nocturnal burrow-nesting storm-petrels and shearwaters which mainly nest on remote islands. Periodic censuses are therefore crucial to obtain a complete picture of what’s going on in terms of changes in population size and distribution.
Setting a baseline
Importantly, as well as allowing comparisons with previous censuses, the results also provide a baseline for assessing future impacts on our seabirds from growing pressures such as climate change, offshore windfarms, outbreaks of HPAI ‘avian flu’ and other diseases, and for measuring the success of conservation actions such as the removal of invasive non-native mammals from islands. For example, the completion of Seabirds Count in 2021 came just before severe outbreaks of HPAI avian flu affected our seabirds in 2022-23, and together with repeat surveys this year, it has provided the opportunity to assess HPAI population-level impacts on badly hit species such as Northern Gannet and Great Skua.
A nod to the fieldworkers
Seabirds Count was a huge undertaking, with data collected over a 7-year period by around 1,000 volunteer and professional surveyors whose passion and commitment to the project saw them spending many hours counting seabirds from land and sea.
Fieldwork during Seabirds Count (c) Tim Dunn
Colony locations were very diverse and included ‘seabird cities’ along our sea-cliffs, remote islands only accessible by boat (with multi-day stays often required to survey storm-petrels and shearwaters), windswept moorlands inhabited by skuas and gulls, and towns and cities where many of our gulls now breed. Over 10,000 ‘natural’ sites and more than 5,500 urban 1 km squares were surveyed across Britain and Ireland, generating over 40,000 records.
Thanks also to the deskbound
The analysis and write-up took a further two years, involving dozens of collaborators writing and reviewing chapters as well as collating and checking the data. The amount of planning and coordination required was also immense, involving many people from over 20 organisations. Similarly, without the generous contributions of five marine renewable companies, UK, Welsh, Scottish and Irish governments some of the most important sites and species would not have been surveyed. We extend our thanks to everyone involved in the project.
Seabirds Count revealed that almost half of species that regularly breed in Britain and Ireland have declined over the past 20 years, and just five have clearly increased.
Leach’s Storm-petrel (-78%) and Arctic Skua (-66%) underwent the largest percentage declines, with Black-legged Kittiwake, Common Gull and Great Black-backed Gull declining by more than 40%, and Northern Fulmar and Arctic Tern by 35%. Another four species including Atlantic Puffin declined by 15–24%.
By contrast, there were modest increases for Great Skua (14%) and Razorbill (18%), a 38% increase for Northern Gannet, and large increases of 152% for Roseate Tern and a whopping 1,612% for Mediterranean Gull. Five species remained stable (change within +/-10%) – Great Cormorant, Common Tern, Sandwich Tern, Black Guillemot and Common Guillemot.
Sandwich Tern pair and chick (c) Chris Gomersall (rspb-images.com)
Trends were less certain for another four species – Manx Shearwater, European Storm-petrel, Herring Gull and Lesser Black-backed Gull – due to methodological improvements and better coverage in Seabirds Count. Populations of the first two have probably increased, but by an unknown amount overall. Natural-nesting populations of the two gull species have declined by over 40%, but it is likely that urban-nesting gulls have increased, including the colonisation of some inland towns not occupied during the previous census.
Scotland saw the largest and most widespread declines, whereas many populations in England, Wales and Ireland increased. However, with Scotland hosting around half of all our seabirds, trends there have driven an overall decline across Britain and Ireland. Causes of decline include reduced availability of food due to climate change, fishery management and agriculture, whilst severe weather events such as winter storms can cause mass mortality events for seabirds such as auks and European Shag.
The Seabirds Count population estimate for all 25 species was around 4.6 million pairs of breeding seabirds. For some species, Britain and Ireland hosts a large proportion of their global or regional breeding populations, including most of the world’s nesting Manx Shearwaters, Northern Gannets and Great Skuas. A further two species have over half of the North Atlantic population breeding here: Lesser Black-backed Gull and Common Guillemot.
In addition to these, five species have over 30% of their North Atlantic population breeding in Britain and Ireland: European Storm-petrel, European Shag, Herring Gull, Roseate Tern and Razorbill. The Seabirds Count results therefore make an important contribution to our current understanding of seabird population sizes in the wider North Atlantic region.
Reasons for hope
Not all species have declined, and trends varied between countries and regions. For example, although Common Guillemots declined overall, this was driven by trends in Scotland whereas the smaller populations in England, Wales and Ireland all increased. Seabird conservation projects and ongoing management have also led to local or regional increases in some species, with terns and burrow-nesting species good examples.
Terns have benefitted from annual management to protect colonies from vegetation succession, predation and human disturbance, whilst burrow-nesters such as Atlantic Puffin, Manx Shearwater and European Storm-petrel have increased on some islands following the removal of invasive non-native mammals.
However, to halt and reverse the overall decline in our seabird populations, much more needs to be done to protect these birds and their breeding and foraging areas from the multitude of threats they face.
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