The results of Butterfly Conservation’s annual Big Butterfly Count reveal that this was the poorest summer for common garden butterflies since the count began in 2010.
While the long-term trends of butterflies and moths tend to result from human activities such as habitat destruction and climate change, short-term changes, from year to year, butterfly generation to generation, are typically caused by natural factors such as the weather and populations of parasites.
So, in cold, wet summers, such as in 2012, butterfly populations often crash, while in good summers, such as 2013, they bounce back.
The results of big butterfly count 2016, however, don’t fit this pattern. It was a pretty good summer with above average temperatures – yet butterflies on the whole fared badly.
The average number of individual insects of the 20 target species seen per 15 minute count during big butterfly count 2016 was the lowest recorded since the project began in 2010. A mere 12.2 individuals per count were recorded, down from 13.4 per count in 2015, 14.7 in 2014 and a whooping 23 per count in 2013.
The top 5 most abundant species in each UK country were as follows:
‘It’s surprising that numbers were even lower than during the cold, wet and thoroughly miserable summer of 2012, as this summer’s weather was distinctly better. Sure, the sunny weather was patchy: the far north-west enjoyed a fine spring and the south-east a good late summer, but the bulk of the UK suffered regular periods of poor weather, at least until the weather stabilised in mid-August.
‘The species that declined most this year either spend the winter as hibernating butterflies, like the Peacock and Small Tortoiseshell, or as hibernating larvae, like the Gatekeeper and Meadow Brown. This suggests that the unseasonal mild and wet winter had a big impact on the numbers that hibernated successfully. It’s also likely that predators and diseases were not checked by cold winter weather.
‘Additionally, some of the butterflies that fared poorly this year breed on low plants growing in pockets of bare ground amongst taller vegetation, such as the Small Copper and Common Blue. The mild winter and wet spring ensured that ground vegetation – especially coarse grasses – grew rampantly, covering the bare ground pockets containing the butterflies’ diminutive food plants resulting in food shortages.
‘The good news is that 36,000 people contributed to Big Butterfly Count, which shows that people care deeply about our butterfly fauna. Had counts taken place 40 years ago, during the long hot summer of 1976, the data would show how horrifically our common butterflies have declined – by orders of magnitude. Our base line for valuing butterfly abundance has shifted downwards.
‘At the National Trust we care for many of the UK’s top butterfly localities, so butterflies are high up on our agenda. And we want to see more butterflies in our farmed countryside, and in our gardens.
‘Perhaps our butterflies now need a traditional cold winter, as well as more scientific research and more recorders.’
National Trust’s butterfly expert
Click here for more about the Big Butterfly Count and view the full results.
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