Wednesday, 5 April 2006

Common Moths undergo pronounced decline

It is about this time of year that I first put out my moth trap; a powerful light positioned above a collecting box. This enables me to record the many different species of moths that are nocturnal visitors to my garden, which would otherwise go unnoticed. The special mv bulb emits a light that is particularly attractive to moths, and those that collide with the bulb drop into the box below, ready to be identified and released the next morning. At the height of summer, following a warm, dark night, there may be dozens of moths in the trap.

Moth trapping is more than just an increasingly popular hobby, because the information collected can tell us about changes in the distribution and abundance of many of the 2,500 moth species to be found in Britain. Systematic recording using moth traps is at the centre of a new study published by Butterfly Conservation and Rothamsted Research. The Rothamsted network of light traps has been operating since 1968, collecting information from an average of 83 traps per year at sites across a range of habitats, from gardens and woodland through to moorland and coastal sites. An analysis of the trapping records, funded by the Esmée Fairbairn Foundation, has highlighted some staggering changes to the populations of many of our ‘common’ moths. The study charted what happened to 337 moth species over the period 1968 to 2002 and showed that two-thirds of the species had undergone a decline. The populations of 75 species had declined by over 70%, with an additional 57 species showing declines of over 50% and 60 species showing declines of over 25%.

Perhaps the most alarming thing about these findings is that virtually none of the declining species was previously thought to warrant any conservation action – these are species regarded by many as being ‘common and widespread’. Some of the biggest declines have hit familiar garden species, like Heart and Dart, Garden Carpet, Scalloped Oak and Common Wainscot. Since those species that use gardens tend to be generalists, the fact that they, too, are in decline should be sounding alarm bells. The reasons for such a general decline across species are likely to lay with habitat loss and a decline in habitat quality, with increasing pesticide use, light pollution and global climate change also playing a part.

Although the study did reveal an increase in a small number of moths, these were typically introduced species or those expanding their range northwards from the Continent. The results reinforce what many of us have noted over the years, a general reduction in the number of moths seen in car headlights while driving about at night and smaller catches in our traps.

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