Simon Wotton dissects this years survey results.
The 29th annual report of the BTO/JNCC/RSPB Breeding Bird Survey (BBS) and Waterways Breeding Bird Survey (WBBS) has just been published, documenting the 30th year of fieldwork.
The report documents the population trends of widespread UK breeding bird species during the periods 1994–2023 and 1998–2023 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, for 119 species using BBS data and 28 waterway specialists using WBBS data. The results are used widely to set priorities and help inform conservation action.
The full BBS report can be downloaded here: BTO;JNCC;RSPB BBS Report 2023
2023 summary
In 2023, 2,751 dedicated and skilled observers gave their time to survey 3,931 1km-squares selected randomly across the UK. For this thirtieth year of fieldwork, UK coverage was close to the (pre-covid) 2019 levels, an encouraging sign that the scheme has not been adversely affected by restrictions in 2020. Some 7,015 different squares have been covered in total since 1994, with 178 covered in each of the 30 years. Just over 100 volunteers have carried out BBS fieldwork in all of its 30 years.
The most widespread species, as measured by the percentage of squares covered in 2023, were Wren (93%), Woodpigeon (91%), Blackbird (90%), Robin (88%) and Carrion Crow (87%).
For the UK, it was possible to produce robust trends for 119 species. Between 1995 and 2022, 35 species showed significant long-term increases – the greatest increase shown by Red Kite (+2,232%). 42 species showed significant long-term declines – the steepest decline shown by Turtle Dove (-97%). There were some significant changes between 2022 and 2023: 20 species showed a significant increase (the greatest by Firecrest, +84%), and 9 showed a significant decrease (the steepest by Kingfisher, -38%).
Red Kites and Turtle Doves have seen very different fortunes over the life of this survey. Norman Norris/Andy Hay. (c) RSPB Images.
Across the UK and in individual countries, there are widespread declines, between 1995 and 2022, among our aerial insectivores, including Swift (-66%), Swallow (-24%), House Martin (-44%), Spotted Flycatcher (-68%) and Pied Flycatcher (-59%).
BBS background
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.
BBS methods
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. 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 2022–23 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’ (27-year) trend, a one-year change is presented.
The BTO/JNCC/RSPB Breeding Bird Survey is a partnership jointly funded by the BTO, RSPB and JNCC, with fieldwork conducted by volunteers.
For more information contact Simon Wotton, Senior Conservation Scientist, Leah Kelly, Conservation Scientist, or Lydia Tague, Science Communications Executive, or follow us on Twitter @RSPBScience #WeBS #wetlandbirds.