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Home » Key Findings » Overall changes in abundance
Overall changes in abundance
Collated indices of abundance are calculated for 50 species and generations. The average of these indices gives an indication of how well butterflies have fared in general.
As a result of the generally poor summer weather in 2004, numbers of many species of butterfly might be expected to have been rather depressed, but this was not generally the case and 2004 proved to be an above average year for butterflies and almost as good as 2003. The warm dry May may have benefitted the young stages of some species reducing the effect of the poor weather later in the season.
Fluctuations in the mean index of abundance. Values are means (± SE) of collated index values for 33 species.
Collated indices were calculated for 50 species and generations. Of these, 23 showed an increase between 2003 and 2004, 26 a decline and one no change at all. Some of the changes were very small. For 33 species (second generation/flight only of bivoltine / Spring/Autumn species) for which collated indices are most reliable, 15 showed an increase, 17 a decrease and one no change.
