Shifting Butterfly Baselines

Meadow Brown

So the results are out. 2012 was the worst year for butterflies in the UK since detailed national population monitoring began in 1976 (see more results here).

On first hearing the results at the recent National Butterfly Recorders’ Meeting, myself and the others around me were shocked, if not entirely surprised, as species after species were revealed to have suffered big year-on-year declines or to have reached their lowest ever ebb in the UK Butterfly Monitoring Scheme (www.ukbms.org) run by Butterfly Conservation and the Centre for Ecology & Hydrology.

However, appalling though the results were, the species declines are not what’s stuck in my mind. Perhaps I’m just a bit ‘battle hardened’ when it comes to the parlous state of the UK’s butterflies. But I was shocked by two things in particular in the 2012 results.

The first was how good 2011 now looks in the population trends for some species. At the time, and it’s not so long ago, the summer of 2011 seemed awful. It was the coldest summer for 18 years and butterfly numbers dwindled away after a promising spring. Now, the summer of 2012 has given us some perspective and the preceding one seems almost balmy in hindsight.

Even more worrying, though, to me is the situation of the Meadow Brown. The UK’s most abundant butterfly, the Meadow Brown is ubiquitous practically anywhere with long grass during the summertime. Contrary to expectations, considering the weather, the Meadow Brown had a great year in the summer of 2012.

I noticed it myself during my own recording in the South West, and similar views were expressed by numerous recorders across the country. It is reflected in the results of Butterfly Conservation’s various schemes too. Meadow Brown was the most abundant butterfly in the Big Butterfly Count, up 186% on the previous year, and also in the Wider Countryside Butterfly Survey, where almost twice as many Meadow Browns were counted as in 2011. The UK Butterfly Monitoring Scheme results released recently, confirmed the case; Meadow Brown numbers were up by over a fifth on transects.

So, everyone agrees that the Meadow Brown, against all the odds, had a fantastic year and its abundance made a strong and lasting impression on butterfly recorders in an otherwise dire summer.

However, and this is the point, although Meadow Brown numbers were up considerably in 2012, they were still only average for the species since the 1970s. I found this deeply disappointing, disturbing even. What seemed like a spectacularly good year for a common butterfly turns out to be a mediocre performance looking back across the past few decades.

I’m suffering from shifting baseline syndrome. This term was coined in a 1995 scientific paper by Professor Daniel Pauly, a leading scientist studying global fish populations, but the concept is an old and intuitive one. We sense and measure change from reference points (baselines), but these themselves change over time. Thus, the Meadow Brown numbers in the summer of 2012 seemed high because we are using recent poor summers as our reference point.

We’ve forgotten that prior to that the baseline abundance of Meadow Browns was much higher. In this case, the UK Butterfly Monitoring Scheme, now in its 38th year, is able to put us straight, at least back to a mid-1970s baseline.

It is an alarming phenomenon. As time goes by and our butterfly and moth populations continue to decline, we remember less and less about how things used to be. We become grateful for the seeming abundance of Meadow Browns in 2012, rejoicing in what seems like a massive comeback, whereas butterfly enthusiasts of old might have wept in response the same sightings. We’ve lost so much of our wildlife in the UK over the past 60 years or so, that there are fewer and fewer people left who can remember what things were like before the post-war drive for agricultural efficiency decimated our landscapes.

We must resist shifting baseline syndrome and our long-term recording and monitoring schemes will help. Our aim should be not only to halt the decline of the UK’s butterflies and moths and to save threatened species from extinction in our islands, but to restore populations back to once-healthy baselines.

Richard Fox

Surveys Manager

Follow on Twitter: @RichardFoxBC