Long-term butterfly monitoring scheme in Britain.

Briefly, at each site the recorder makes a series of counts, walking a fixed route once a week from April to September, noting any butterflies seen within 5 metres. To provide standardisation, walks are carried out only between 10.45 and 15.45 BST, and then only if the weather meets specified criteria. Transect routes are divided into sections, usually according to changes in habitat, so the scheme provides information on habitat preferences of different species, and gives a means of objectively assessing the effects of management on species.

Over 100 sites from the whole of Britain and Northern Ireland now contribute to the Scheme each year. Results are analysed in several different ways. At each site, the mean weekly count of each species is totalled to provide an annual index of abundance.

The index of abundance is not a population estimate, but has been shown to be related to propulation size (Pollard, 1977). The annual indexes of abundance from all sites are then collated to give either an "all sites" or regional index (Moss and Pollard, 1993). The fluctuations of the regional or "all sites" trends, can be used as a baseline for comparison with specific sites to assess the effects of local management (Pollard and Yates, 1993).