BBS trends for 2020
In 2020, England, the Channel Islands and Isle of Man COVID-19 restrictions were eased in time for Late visits but in Scotland, Wales, and Northern Ireland, some restrictions continued through the Late visit period, understandably, resulting in limited coverage. Reductions in Scotland, Wales and Northern Ireland were so severe that the sample of surveyed squares was too small and seasonally biased to give reliable trends. Travel restrictions also caused subtle habitat biases, with fewer upland and remote habitats surveyed. As a consequence, we were only able to estimate some trends for England, but unfortunately not elsewhere.
Below, we provide the 2020 trend table for download in Excel format, as in previous years, along with the 2020 population trend graphs. These results are for the species for which we were able to estimate robust trends but the change estimates reported should still be treated with caution because uncertainties remain, such as the precise impact of a shift in average survey dates compared to previous Late visits. For some species we can only report either the all-time or the one-year trend. Given the constraints of the data, and a desire to limit over-interpretation of these indicative trends, we have not produced the usual confidence intervals around the smoothed trends and cannot infer which changes are statistically significant.
A research paper detailing the process of identifying which species’ trends appear to be least impacted by COVID-19 coverage is being prepared for publication. For a more informal description of the 2020 data analysis and interpretation of these data, please see pages 10 and 11 of the BBS Report 2020.
BBS population trend graphs
All BBS graphs are displayed in the same way. Beware, however, that the index axis does vary in scale. As mentioned, we have not produced confidence intervals around the smoothed trend this year.
BBS index graphs show:
- smoothed trend — dark green line
- annual index values — blue dots
Barn Owl - England
BBS trend table
Trends for species in brackets are reported with caveats:
We do not report population trends for five species of gull (Black-headed, Common, Great Black-backed, Herring and Lesser Black-backed), as a large proportion of the records are of non-breeding, wintering or migratory individuals.
Trends for rare breeding species with substantial wintering populations (e.g. Fieldfare) are excluded.
Trends for Common Tern, Cormorant and Grey Heron are reported with the caveat that counts may contain a high proportion of birds away from breeding sites.
Trends for Barn Owl are reported with the caveat that the BBS monitors nocturnal species poorly.
Counts for Lapwing are corrected to exclude counts from non-breeding flocks.
The ‘Sample’ for the long-term trend refers to the mean number of squares per year on which the species was recorded during BBS. Normally the one-year trend sample size would also give the average number of squares per year, but as 2020 coverage was so reduced, the sample size given this year is simply the number of squares each species was recorded on in 2020.
Trends are presented as the percentage change over the whole 24-year survey period and the most recent one-year change from 2019 to 2020.
The long-term changes cover the lifetime of the survey, with the first and last years removed for statistical reasons.
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