Purple Hairstreak (Favonius quercus)
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© Eddie John
The Purple Hairstreak is primarily a butterfly of oak woodland that spends most of its time in the tree canopy and is infrequently seen on butterfly transects though it may be one of the commonest butterflies on a site. Caterpillars feed exclusively on oaks (Quercus spp.) and colonies can sometimes be found on isolated trees. (For further details on this species see http://www.butterfly-conservation.org/).
Status details :
Status since 1976 is Rapid decline with a decrease of -62.7%
Status over the last 20 years is Rapid decline with a decrease of -56.5%
Status over the last 10 years is Stable with a decrease of -20.9%
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 elusive canopy dwelling butterfly does not lend itself to being monitored by the transect method. Therefore not surprisingly the data show no significant trend, though at some sites numbers recorded are sufficient to show both increases and declines. After a substantial drop in abundance at monitored sites in the mid-1980's numbers have risen back and fluctuated little around the average for the series since the early 1990's.
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 Hairstreak has been recorded from 409 transects in the Butterfly Monitoring Scheme. Of these, annual indices of abundance have been calculated from 429 sites, with an average index of 5 individuals per site.
For 219 of these sites, Purple Hairstreak has been recorded well enough to calculate annual indices of abundance in more years, allowing trends to be calculated.
In 2017, 1265 individuals were recorded from 117 sites, producing annual indices at 101 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
|Colonised sites (11)|
|Extinct sites (9)|
|Stable sites (132)|
|Increasing sites (15)|
|Declining sites (43)|