Purple Emperor (Apatura iris)
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© Nick Greatorex-Davies
In Britain the Purple Emperor is an elusive and generally rare butterfly that is confined to well wooded areas in southern England usually where Goat Willow (Salix caprea) (its chief main foodplant) grows in abundance. (For further details on this species see http://www.butterfly-conservation.org/).
Status details :
Status since 1979 is Stable with a increase of 42%
Status over the last 20 years is Stable with a increase of 41%
Status over the last 10 years is Rapid decline with a decrease of -61.4%
Log collated index plot
This chart shows the index of abundance (LCI = Log Collated Index) over time. It shows fluctuations in
populations from year to year, and is scaled so that the average index over the whole series is equal to 2
(horizontal line). For greater detail about how this index is derived, click on the green question mark above.
Trend description :
This very localised canopy species is rarely seen and the transect method is not the most suitable method for monitoring it. Despite this, Purple Emperors have been seen on more and more transect sites and although not significant the long-term trend is of an increase across the UK. It is recorded regularly on a number of transects in the SW/SE including West Dean Wood in West Sussex and Bentley Wood in Wiltshire.
This map shows the distribution between 1995 and 2016. Data is derived from the Butterflies for the New Millenium dataset via the NBN Gateway
This chart shows the average number of butterflies seen on transects between Arpil and October across all sites (fitted values from a Generalised Additive Model). The blue line gives average counts over the full BMS series (1976 to date) and the red line gives the average for the last year.
This map shows symbols for the mean abundance at transect sites, with the colour of the symbol reflecting the level of abundance. Means are over all years. Grey background squares are the occupied cells as shown by the Butterflies for the New Millenium over the previous ten year period.
In total, Purple Emperor has been recorded from 79 transects in the Butterfly Monitoring Scheme. Of these, annual indices of abundance have been calculated from 120 sites, with an average index of 0 individuals per site.
For 30 of these sites, Purple Emperor has been recorded well enough to calculate annual indices of abundance in more years, allowing trends to be calculated.
In 2018, 49 individuals were recorded from 15 sites, producing annual indices at 14 of these.
Links to counts
This map shows the trend in abundance at particular transect sites for which data has been received within the last five years. Trends (increasing, declining or stable) are assessed at sites where the species has more than five years of annual index data. Use the option boxes below to view plots for individual sites.
Links to lists of sites with particular statuses
|Extinct sites (1)|
|Stable sites (10)|
|Increasing sites (3)|
|Declining sites (2)|