The 28th annual report of the BTO/JNCC/RSPB Breeding Bird Survey (BBS) and Waterways Breeding Bird Survey (WBBS) was published last week. In today’s blog, Senior Conservation Scientist Simon Wotton explains the latest results and the incredible effort that goes into producing this report.
BBS and WBBS document the population trends of widespread UK breeding bird species during the periods 1994–2022 and 1998–2022 respectively. These are the main schemes for monitoring the population changes of the UK’s widespread breeding birds, providing an important indicator of the health of the countryside. Trends are produced each year, with 118 species again reported using BBS data and 28 waterway specialists using WBBS data. The results are used widely to help inform conservation action.
2022 summary
For the UK, it was possible to produce robust trends for 118 species. Between 1995 and 2021, 37 species showed significant long-term increases – the greatest increase shown by Red Kite (+2,105%). 41 species showed significant long-term declines – the steepest decline shown by Turtle Dove (-97%) as mirrored in the recent national Turtle Dove survey.
The BBS report suggests that Swift numbers have declined by 62% in the UK since 1995, with similar reported declines in England (-62%), Scotland (-58%) and Wales (-74%). A similar figure for Northern Ireland is not presented, as the species is not recorded in enough BBS squares here to be able to produce a robust trend. You can help by using Swiftmapper and submit records of breeding Swifts.
Swift numbers have declined by 62% since 1995 (c) Ben Andrew (rspb-images.com)
Phenomenal coverage
In 2022 a total of 2,738 dedicated and skilled observers gave their time freely to survey 3,919 1km-squares selected randomly across the UK. This is an encouraging recovery following the covid restrictions of 2020.
Not only that, mammal monitoring was conducted on 88% of squares in 2022. In 2022, a minimum of 14,494 km was walked by BBS volunteers during the surveys. A total of 231 species were recorded in 2022 on BBS squares. The most widespread species, as measured by the percentage of squares covered in 2022, were Wren (92%), Woodpigeon (91%), Blackbird (89%) and Robin (87%).
BBS background and history
The BBS was launched in 1994 to provide more representative habitat and geographical coverage than the main survey running at the time, the Common Birds Census (CBC). The CBC ended in 2000, and the overlap period between 1994 and 2000 allowed BTO to develop methods for calculating long-term trends (from the 1960s to the present) using information from both schemes.
The BBS National Organiser, based at BTO HQ, is responsible for the overall running of the scheme, and is the main point of contact for the network of volunteer Regional Organisers. Regional Organisers are responsible for finding new volunteers and allocating squares to observers in their region. At the end of the season they validate submissions made online, and collect paper submissions for inputting.
How do they do it?
The BBS is a line-transect survey based on randomly located 1-km squares. Squares are chosen through stratified random sampling, with more squares in areas with more potential volunteers. The difference in sampling densities is taken into account when calculating trends.
BBS volunteers make two early-morning visits to their square during the April–June survey period, recording all adult birds encountered while walking two 1-km transects across their square. Each 1-km transect is divided into five 200m sections for ease of recording.
Birds are recorded in three distance categories, or as ‘in flight’, in order to assess detectability and work out species density. To assess further the detectability of species the option of recording how birds were first detected (by song, call or visually) was introduced in 2014.
BBS is possible thanks to the efforts of the thousands of volunteer surveyors (c) Heather Stuckey (rspb-images.com)
Observers also record the habitat along the transects, and record any mammals seen during the survey. Surveying a BBS square involves around six hours of fieldwork per year, and the aim is for each volunteer to survey the same square (or squares) every year.
The BBS provides reliable population trends for our commoner and more widespread breeding species. Trends can also be produced for specific countries, regions or habitats. To ensure robust results trends are only produced for species with sufficient data. To judge this we look at the average number of squares on which a species has been recorded per year during the trend period.
For UK BBS trends we consider species above a reporting threshold of 40 squares. For countries within the UK, English Regions and UK WBBS trends, the threshold is an average of 30 squares during the trend period. The one-year change for 2021–22 is shown where the sample size reaches the reporting threshold for one of the longer trend periods. Therefore, if there is a 10-year or ‘all-time’ (26-year) trend, a one-year change is presented.
The full BBS report can be downloaded here.
The BTO/JNCC/RSPB Breeding Bird Survey is a partnership jointly funded by the BTO, RSPB and JNCC, with fieldwork conducted by volunteers.
The Breeding Bird Survey is always on the lookout for volunteers. If you are able to identify UK breeding birds by sight, song and call, then do get in touch. If you have the necessary bird ID skills to take part in the Breeding Bird Survey but want to learn more about survey methods, there are a number of BTO training courses covering this subject.
Continue reading
Would you like to be kept up to date with our latest science news? Email with the heading 'enewsletter' to be added to our quarterly enewsletter.
Want our blogs emailed to you automatically? Click the cog in the top right of this page and select 'turn blog notifications on' (if you have an RSPB blog account) or 'subscribe by email'.