 |
||||||||||||||
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
||||||||
White-letter Hairstreak (Satyrium w-album)
© Eddie John
The White-letter Hairstreak is a very elusive butterfly that spends most of its time high up in the canopy of Elms (Ulmus spp.), on which it breeds, in woodlands and hedgerows. The butterfly is still widespread but far less common than it was before the ravages of Dutch Elm Disease. (For further details on this species see http://www.butterfly-conservation.org/).
Family: Lycaenidae
Status: Rapid decline
Status details:
Status since 1976 is Rapid decline with a decrease of -74.8%
Status over the last 20 years is Rapid decline with a decrease of -78.4%
Status over the last 10 years is Stable with a decrease of -23.4%
Back to the topLog 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 normally elusive canopy species is poorly monitored by the transect method and it is only occasionally recorded on most transects where there are populations. The data show no significant trend. Only at Northward Hill and, early on, Avon Gorge have numbers been recorded in double figures, or even annually (at Northward Hill it was recorded almost annually in at least double figures for a 17 year period, highest count 211 in 1984). At Northward Hill numbers recorded have declined dramatically in recent years though the foodplant, elm, is still abundant at the site.
Distribution...
This map shows the distribution between 1995 and 1999. Data is derived from the Butterflies for the New Millenium dataset via the NBN Gateway (www.searchnbn.net).
View the distribution on the NBN GatewayPhenology...
Phenology plot
Phenology plot
This chart shows the average number of butterflies seen on transects between Arpil and October. The black line gives average counts over the full BMS series (1976 to date) and the red line gives the average for the last year.
Abundance...
Abundance
This map shows symbols for the mean abundance at transect sites, with the size of symbol reflecting the level of abundance. Means are over all years.
Coverage
In total, White-letter Hairstreak has been recorded from 173 transects in the Butterfly Monitoring Scheme. Of these, annual indices of abundance have been calculated from 239 sites, with an average index of 2 individuals per site.
For 98 of these sites, White-letter Hairstreak has been recorded well enough to calculate annual indices of abundance in 6 or more years, allowing trends to be calculated.
In 2006, 166 individuals were recorded from 44 sites, producing annual indices at 34 of these.
This map shows the trend in abundance at particular transect sites. Trends (increasing, declining or stable) are assessed at sites where the species has more than five years of annual index data. Click on the green question mark next to the species name above for more details on how trends are calculated.
Links to lists of sites with particular statuses
• Extinct sites (2)
• Colonised sites (2)
- Stable sites (16)
- Declining sites (4)
