Fluctuations in the abundance of butterflies, 1976–82

Abstract. 1. A scheme for monitoring the abundance of butterflies at about eighty sites in Britain is described. 2. Indices of abundance are presented for twenty‐nine species for the years 1976–82. 3. There are marked differences between species in the scale of annual fluctuations. 4. Some species show correlations between successive index values; for example the summer generation index of Pieris brassicae is highly correlated with the spring generation index. 5. The annual changes in the index values of many species are highly Correlated. The index values themselves also show positive correlations, but these are less strong. 6. The drought of 1976 is believed to have severely depressed populations of many species in 1977. 7. The data do not indicate any general fall in butterfly numbers over the period at the sites in the scheme. 8. The sites are not representative of the countryside as a whole, but, for a number of species, it is considered that the index values reflect wider trends.