The annual Big Butterfly Count is a huge citizen science project run by Butterfly Conservation every year since 2010.
In late July and early August, volunteers find a sunny spot and count how many butterflies and day flying moths (I will just say butterflies from now on for brevity) they see in a 15 minute period across a range of habitats including gardens, parks, fields and woods. The project only records from a target list of 20 species that are found across the country and are relatively easy to identify.
The sheer scale of the project, this year 80,000 volunteers carried out nearly 130,000 counts, yields data that can be taken as a reliable indication of how our butterfly populations are faring. The Sid Valley has an active citizen science population who carried out nearly 200 counts, a small number for reliable statistical analysis but a basis to make useful comments.
This is a brief overview of the 2024 results. More than half of our counts were carried out in countryside and a small number of sites yielded very large numbers of the meadow species which skews our results somewhat and so our valley is not directly comparable with the national picture. We have a high proportion of grassland and no very large urban centre, but we can get useful information from our local data, especially if we make comparisons over time. As there are different numbers of counts per year and per habitat the report focuses on the number of each species seen per count.
Overall, we see more butterflies in our valley than the national average, 12.6 per 15 minute count compared with the national average of 7.1. The numbers of the 20 species seen locally were down from 14.5 per count in 2023, a drop of 13%. The three main meadow species, Meadow Brown, Gatekeeper and Ringlet appear to have done well and the Silver Y moth has jumped up the ranking. These increases could be down to an extra proportion of grassland sites included this year. We will have to wait for a more sophisticated analysis before further comment can be made.
The really alarming figure is the drop in the proportion of the other species seen. This year’s top five accounted for over 81% of the total. Last year, the same species accounted for only 53%. Put the other way, the 15 least seen species dropped from 47% of the 2,090 butterflies recorded locally last year to just 19% of the 2,250 seen this year.
The numbers of Peacocks and Red Admirals per count appear to have halved from last year but this may be another effect of the shift in the proportion of grassland sites surveyed. Some gardeners may be pleased by the apparent decline in the Large White (also known as the Cabbage White because it likes to lay its eggs on cabbage plants which the caterpillars will totally destroy) but its loss is a sign of other problems and not a cause for celebration.
The once common Small Tortoiseshell has almost disappeared from our valley with just 5 recorded. Recent national figures have shown a similar disastrous drop in the numbers of this beautiful butterfly that was so common in my childhood.
A more comprehensive report will be available at a later date.
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