Moth trends for UK macro-moths
BRC is working with Rothamsted Research and Butterfly Conservation to produce updated moth trends for UK macro-moths using the extensive data from the light trap network that forms part of Rothamsted Research’s Insect Survey. The light trap network monitors nocturnal moths across the UK, using a collection of standardised moth traps that are run every night of the year. The network has been running since 1968 and during that period traps have being run in more than 500 location across the country. Each year, around 80 to 100 traps operate ; there is turnover in traps leaving or joining the network.
The Rothamsted Research light trap network data have been used periodically over the years to produce national moth trends with the most recent being presented in 2013 for The State of Britain’s Larger Moths 2013. The trends presented in this study were 40-year trends (1968-2007) and were given for 337 species.
In the current project we adapted the method developed for analysis of butterfly trends by the United Kingdom Butterfly Monitoring Scheme (UKBMS) to the moth data to see if it could provide robust trends. It was also hoped that the new method (Generalised Abundance Index, GAI), combined with the additional years of data collected since the previous analysis, may allow trends to be produced for a larger number of species as well facilitate the production of confidence intervals for the trends produced.
The data used in the analysis contained more than 4.5 million records, relating to 12.5 million individual moths of more than 700 species across 540 traps between 1968 and 2016. Using the analysis we were able to provisionally produce temporal trends for 432 species, increasing the number of species with trends by more than 90 species. Each trend produced also included confidence intervals estimated using bootstrapping. The figure below shows the provisional results for the Garden Tiger moth, Arctia caja, which is a widespread, easily recognised moth that has declined by almost 90% between 1968 and 2016.