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Seabirds Count – the fourth Breeding Seabird Census

The results from Seabirds Count, the fourth census of Britain and Ireland’s internationally important populations of breeding seabirds, were published on 16 November 2023. 

Over 10,000 sites and 25 species were surveyed between 2015 and 2021 to provide a comprehensive update on the state of these populations and gain greater insight into the relationships between them and the pressures they face. 

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Background

The previous national seabird census (Seabird 2000, 1998–2002) counted over eight million seabirds breeding in Britain and Ireland, highlighting our international importance for many seabird species. Since then, there has been evidence of widespread declines in breeding success which may have contributed to declines in the breeding abundance of some species, detected by annual monitoring.

To understand changes in breeding seabird population sizes and distributions, a new census of Britain and Ireland’s breeding seabirds – Seabirds Count – was completed between 2015 and 2021. Its aim was to produce updated population estimates for the 25 species that regularly breed here. These census data provide a foundation for assessing current seabird population health, and so are vital for understanding the conservation status of our internationally important seabirds, the impacts of pressures such as climate change and fisheries on marine environments, and to inform marine planning. 

Seabirds Count, the fourth breeding seabird census of Britain and Ireland, was developed by a steering group consisting of over 20 organisations and was coordinated by JNCC. Census data were collected by approximately 1,000 volunteers and professional surveyors at over 10,000 breeding colonies and more than 5,500 1 km urban squares.  

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Results

Overall, the results from Seabirds Count show a mixed picture when looking at the direction and extent of population change in Britain and Ireland’s breeding seabird populations.

The overall picture is one of declines. Eleven of the 21 species, where we have confidence in their trends, have declined by over 10% since the previous census. However, the picture looks more positive for the breeding populations of five species which have increased by over 10% and a further five have remained stable (Figure 1).

A table of seabirds included in Seabirds Count showing their order in terms of improvement, staying the same or decline. Details are provided in the Seabirds Count publication

Figure 1. Summarised population change for the 21 species, where we are confident in their trends, between Seabirds 2000 and Seabirds Count.

Comprehensive population estimates have been produced for Manx Shearwater, European Storm-petrel, Lesser Black-backed Gull and Herring Gull. However, there is low confidence in their population trends since the last census due to changes in methodology and/or improved survey coverage which means there is insufficient comparability between Seabird 2000 and Seabirds Count population estimates.

Full species’ accounts of Seabirds Count census results can be found in the Seabirds Count publication.

The comparative dataset for Seabird 2000 and Seabirds Count is available to download (revised 13 December 2023). Please note that some errors were found in the original dataset, published on 16 November 2023, which have subsequently been corrected. Any copies of the dataset downloaded prior to 13 December 2023 will contain these errors.  For the corrected data, please download a copy of the revised version.

Little Tern, Roseate Tern and Mediterranean Gull are confidential species and the datasets for these are, therefore, only available on request. A portal that will allow for interactive interrogation of the census data will be available soon via the Seabird Monitoring Programme online database.

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Storm-Petrels and Manx Shearwaters

European and Leach’s Storm-petrels and Manx Shearwaters are nocturnal, burrow-nesting species that have historically been difficult to census accurately. Seabird 2000 was the first census to quantify colony sizes, implementing play-back methods which were developed in the late 1990s. These played a recording of the target species’ calls at sampling points in potential nesting areas to elicit vocal responses from adults occupying sites and used response rates to call-playbacks to estimate colony size. The methodological improvements implemented in Seabird 2000 (1998–2002) (Mitchell et al. 2004) were built upon, and refined during Seabirds Count by embracing new technology, and enabled the delivery of for more accurate population estimates.

Further detail on European and Leach’s Storm-petrels and Manx Shearwater survey methods and analytical processes can be found in their respective species accounts and in the method chapter of the Seabirds Count publication. The dataset used to produce the Manx Shearwater and European Storm-petrel estimates is available to download and survey reports are available on request. Leach’s Storm-petrel is a confidential species and these data are, therefore, only available on request.

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Urban-nesting gulls

Distributions of Herring Gulls and Lesser Black-backed Gulls have changed markedly over recent decades, with a substantial increase in the numbers breeding in urban areas. While standardised methods employed by the Seabird Monitoring Programme (SMP) to survey Herring Gulls and Lesser Black-backed Gulls provide reliable indicators of their natural (i.e. rural) population abundance trends, at the time of the last census there was no reliable equivalent method for their urban (roof) nesting populations, in part due to issues with applying traditional survey methods in urban environments. As such, published national population estimates of Herring Gulls and Lesser Black-backed Gulls from the Seabird 2000 census (Mitchell et al., 2004) are considered unreliable due to likely under-estimation of roof-nesting gull numbers.

To address this gap, a new survey methodology, sampling regime and analytical process were developed and implemented for Seabirds Count, to produce more robust estimates of breeding urban gulls. The survey method consisted of surveying a sample of 1 km squares in urban areas across the Britain and Ireland, stratifying sampling to account for different ratios of urban habitat sub-strata across different regions. The analysis consisted of utilising correction models produced from comparative aerial and ground-based surveys to account for the variable detectability that comes with surveying gulls breeding in urban habitats.

The urban nesting gulls survey was a huge undertaking and added over 5,500 1 km squares to the total sites surveyed during Seabirds Count. The results reveal the substantial numbers of roof nesting gulls in Britain and Ireland, highlighting the importance of this habitat to Herring and Lesser Black-backed Gulls where a significant proportion of their total population now breed.

Results from the urban-nesting surveys can be found in the respective species accounts published in the Seabirds Count publication. A full technical report is currently in production and will be available in due course.

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Results in seabird Special Protection Areas (SPAs)

Special Protection Areas (SPAs) are areas on land or at sea which provide protection for rare, threatened, or vulnerable bird species, and frequently include seabirds. Seabirds Count surveys covered breeding seabird colonies in 173 SPAs across Britain and Ireland where at least one seabird species was a qualifying feature.

While census data show that some species are doing well within SPAs, results indicate that many species are declining. Seabirds Count SPA population estimates and percentage changes since Seabird 2000 for feature species are summarised in each individual species’ account. Furthermore, a full summary of all population estimates, and total percentage change recorded for each species across all 173 SPAs is also available to download.

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Seabirds Count Steering Group Partners

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Additional Funders

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Seabird censuses

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