It’s always fun to trace the chain of Chinese whispers between primary research and scary news stories about the ravages of climate change. Many BBC science stories are particularly easy to trace back to source, based as they are on a single scientific paper, from which they are separated by only a single press release. But even when the whisper chain is a short one, there is plenty of room for the distortion of sobre science to alarmist headline, especially when the press release contains everything you need for the job. So it was with the BBC’s ‘Bid to aid daddy longlegs numbers’ published on Thursday:
Climate change is killing off cranefly and in turn threatening the survival of upland wild bird species that feed on them, RSPB Scotland has warned.
The Telegraph also reported the story:
Daddy longlegs decline could spell extinction for golden plover
So did the Daily Mail, which isn’t even supposed to believe in this new-fangled climate change business:
Warmer summers ‘killing off daddy long legs and beloved British birds’
And Science Daily:
Drop In Daddy Long Legs Is Devastating Bird Populations
All the stories drew entirely from a press release issued by RSPB Scotland, which they have simply condensed and bolted on their own introduction and headline. (Science Daily also spliced in an extra quote from a co-author of the research paper). Here’s the headline of the presser:
Warmer weather pummels plovers
Craneflies – better known in the UK, at least, as daddy longlegs – are gangly insects that appear en masse in temperate regions for a few weeks in spring, providing a bonanza food source for breeding birds and other predators. Judging by the news stories, climate change is killing them off by drying out the soil in which their larvae live, which is in turn killing off the birds that rely on them.
But according to the research paper, published in the journal Global Change Biology, it is far from clear that golden plovers are even declining, let alone being ‘killed off’, ‘pummeled’ or ‘devastated’, as shown in the paper’s Figure 5:
The data represent just a single, small population. But neither is there much evidence that golden plovers are undergoing a national, European or global decline. Lead author of the paper, Dr James Pearce-Higgins of RSPB Scotland, confirmed this when we spoke to him on the phone.
The population studied by Pearce-Higgins and his colleagues sits on the southern edge of the species’ range in the English Peak District. This was by design, in that the intention was to examine how global temperature rises might affect species distributions. While evidence is accumulating that many species expand their ranges northwards in response to a warming trend (in the Northern Hemisphere), evidence for predicted contractions at the southern limit of species’ ranges is sparse. But even in what might be expected to be a particularly sensitive population, there is no downward trend in plover numbers over the last 35 years, despite a local rise in mean August temperatures of 1.9C over that period.
That is not to say, however, that temperature rises are not having an effect on the population. Pearce-Higgins et al have developed a model that does seem to explain much of the variation in plover numbers over the 35-year period. The model integrates previous work by the group, which found that plover mortality rises in cold winters, with new data showing that high August temperatures kill off cranefly larvae leading to fewer adults emerging the following spring when the birds are feeding their chicks. So, rising temperatures are a double-edged sword for plovers. Mild winters increase survival, but hot summers reduce breeding success. The model suggests that there might have been a switch in the relative importance of these two effects in recent years, with spring food availability becoming a more important determinant than winter temperature of population size.
There remains, of course, a lot of unexplained variability in the system, and Pearce-Higgins is reticent to attribute any short-term population fluctuations to specific effects:
From about the mid-’90s to mid-2000s, when the time series stops, there’s actually – although we don’t put this in the paper – there’s actually a significant decline in golden plover numbers […] I guess I was being cautious really, in terms of attributing the decline to what’s going on, particularly as, if you look across the whole of the UK, there isn’t much evidence of a golden plover population decline, and I’m very well aware that lots of other factors are affecting their population […] If you take the trend from the mid-90s through to when we finish about 2005, there is a decline there, but obviously that’s an arbitrary cut-off.
So, all the news stories – and, indeed, the RSPB’s own press release – are wrong to suggest that climate change is reducing plover populations. While they all treat the issue in the present tense, as if golden plovers are being devastated by climate change in the here and now, the only evidence of population decline presented by paper comes from the application of the model to future population trends.
The researchers take the 1.9C local temperature rise over the past 35 years and extrapolate it over the next 100 years. The resulting rise of 5.2C above the 1971-2005 mean would, according to their model, result in a 96% chance of extinction of the population. A 1.9C local rise in August mean temperatures would seem very large, however, when global temperatures have increased by 1C over the past century, and it’s certainly much bigger than the rise in temperature experienced by central England over the same period.
The researchers also apply their model to a range of other temperature scenarios:
In other words, things have to get pretty warm before even a small population on the edge of the species’ range starts to feel the heat. And yet it is only the extrapolation of the 1.9C rise that makes it into the press release and, therefore, the news stories.
Not only have news reports confused current declines with possible declines in the future, but they deal only with an apparently unrepresentative worst-case scenario, and they apply data from a single population at the southern extremity of the species’ range to the species as a whole to announce that a species that isn’t even declining is being driven to extinction.
Given that all the news coverage of the paper was based almost verbatim on the press release, it is perhaps surprising that Pearce-Higgins is happy with how the RSPB presented the research:
I don’t think the press release is particularly misleading really
‘That’s the challenge’ he says,
to try to get across what is quite a complicated message, but with an important underlying message, in a way that is acceptable to the media, but that also does justice to the science.
Readers can make up their own minds whether the RSPB press release does justice to the science. But it certainly seems to have been acceptable to the media, who didn’t need to look any further to get their alarmist climate stories. One particular quote in the RSPB press release proved particularly attractive, being used by the BBC, Telegraph and Daily Mail. It’s from Pearce-Higgins:
This is the most worrying development that I have found in my scientific career to date.
Perhaps that’s what he means by the ‘important underlying message’.