Big Butterfly Count data proves its worth

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Citizen science is flourishing in the UK and around the world, particularly as a means of monitoring wildlife and the environment at a large scale, and Butterfly Conservation's Big Butterfly Count is a great example. With less than 16,000 Counts submitted in the inaugural year of 2010, participation has soared almost four-fold over the eight years of the event, with an amazing 62,500 Counts contributed by 60,400 people this summer.

Nevertheless, some scientists and policy makers remain wary of the results of mass-participation citizen science. Their concerns stem both from the involvement of large numbers of often inexperienced members of the public, which may lead to species identification errors, and the use of simple sampling techniques, which are necessary to enable untrained volunteers to take part. As a result, they argue, the data gathered and the results obtained are unreliable and of limited use.

This summer, a new study comparing the data gathered through Big Butterfly Count with the rigorous sampling of the UK Butterfly Monitoring Scheme (UKBMS) - the major UK-wide monitoring programme for butterflies, has bolstered the credibility of the citizen science scheme. Leading the research, Butterfly Conservation’s Senior Ecological Statistician, Dr Emily Dennis, showed that despite all the potential pitfalls in the Big Butterfly Count methodology (e.g. non-standardised sampling and unverified records) the scheme could produce butterfly population trends that closely matched those from the UKBMS. The study was a collaboration between Butterfly Conservation, the University of Kent and the Centre for Ecology & Hydrology.

Looking just at records from the three-week period in which Big Butterfly Count takes place, species population growth rates derived from the UKBMS mirrored those from Big Butterfly Count over the years analysed (2011-2014).  Of course, butterfly flight periods shift from year to year depending on the weather (many were early in 2017, for example, due to the warm spring) and this presents a problem for a short-term ‘snap-shot’ survey such as Big Butterfly Count. In some years the Count period may fall right on the peak in numbers of a particular species, but in others it may take place when populations are only just starting to emerge or already ebbing naturally. The study found that the impact of these natural variations on the Big Butterfly Count trends could be corrected using weather data.

Mass-participation citizen science projects such as Big Butterfly Count are not a replacement for the standardised monitoring of the UKBMS. For one thing, Big Butterfly Count only generates trends for 18 widespread butterflies, whereas the UKBMS also measures the changing fortunes of almost all of our threatened butterfly species. But the Big Butterfly Count also has some advantages; it samples private gardens and urban areas to a much greater extent than the UKBMS, and another recent study suggested that butterflies are faring particularly badly in urban areas. As a result of the new research, it is possible that Big Butterfly Count data, which are already used in distribution mapping after verification by County Recorders, could also be incorporated into the UK population trends of widespread species to represent more fully the range of habitats in which they live.

The full paper is open access and available online:

Dennis, E.B., Morgan, B.J.T., Brereton, T.M., Roy, D.B., Fox, R. (2017). Using citizen science butterfly counts to predict species population trends. Conservation Biology http://onlinelibrary.wiley.com/doi/10.1111/cobi.12956/full

by Richard Fox, Head of Recording

Follow Richard on Twitter @RichardFoxBC