December 8, 2016, by Tim Radford
The Common Blue hasn’t fared well in the UK’s recent warm winters. Image: Andreas via Flickr
The floods, heatwaves and droughts caused by climate change may explain the loss of butterflies in the UK in recent years, rather than global warming.
LONDON, 8 December, 2016 – British scientists have begun to establish just what it is about climate change that might have precipitated a decline in British butterflies.
And it may not be the gradual but inexorable global warming as a consequence of the combustion of fossil fuels that is behind the decline. It may instead be extreme events – calamitous floods, unprecedented heatwaves and extended droughts.
The scientists report in the Journal of Animal Ecology that they had at their fingertips some high-quality data from the UK Butterfly Monitoring Scheme, which recorded abundances of 41 species of butterfly at 1,800 sites over a period of 37 years.
Since the UK also has weather records to match, they could begin to read the impact of climate change on a much-loved, and much-studied, group of insects.
Gradual climate change is likely to deliver bad news for some species, but opportunities for others. In a temperate zone, some creatures can simply shift their ground, or change the timing of their breeding patterns. So biologists have been watching closely.
“A novel finding of this study was that precipitation
during the pupal (cocoon) life stage was
detrimental to over one quarter of the species”
In the high latitudes, butterflies have responded by shrinking in size. In the alpine regions, species have moved uphill as temperatures have risen. In crowded, intensively farmed but conservation-conscious Britain, some species have fared badly.
And it now turns out that extreme weather – itself linked to climate change – is part of the problem. Those butterflies that overwintered in the UK were hit by unexpected heat in winter but benefited from extreme heat in summer.
Extreme cold in winter helped, but cold spells in summer created different problems.
“A novel finding of this study was that precipitation during the pupal (cocoon) life stage was detrimental to over one quarter of the species,” says Aldina Franco, a conservation ecologist at the University of East Anglia in the UK.
“This study also found that extreme heat during the overwintering life stage was the most detrimental extreme weather event affecting over half of UK species. This may be due to increased incidences of disease or potentially extreme hot temperatures acting as a cue for butterflies or their larvae to come out from overwintering too early, and subsequently being killed off by temperatures returning to colder conditions.”
Extreme heat in the adult stage, however, helped at least one-third of UK species. “This is not an unexpected finding, given that butterflies are warmth-loving creatures. Years with extreme warm summers and winters may have mixed effects. For example, although the summer was warm, the number of butterflies counted during the Big Butterfly Count was particularly low,” Dr Franco says.
“Our study indicates that this could have resulted from the detrimental effects of the warm winter; for example, the recent low counts of Gatekeeper, Common Blue, Comma, Peacock and Small Tortoiseshell butterflies could be explained by their negative response to warm winters just experienced.” – Climate News Network
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.