Brown Hairstreak (Thecla betulae)
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© Eddie John
The Brown Hairstreak is an elusive species of hedges, scrub and woodland edges where it requires a good supply of young Blackthorn (Prunus spinosa) growth for breeding. It has declined substantially in Britain due to extensive hedgerow removal and the annual flailing of many remaining hedges. (For further details on this species see http://www.butterfly-conservation.org/).
Status details :
Status since 1983 is Stable with a decrease of -12.6%
Status over the last 20 years is Rapid decline with a decrease of -54.5%
Status over the last 10 years is Stable with a decrease of -5.0%
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 rare canopy dwelling species is not suited to transect monitoring, however it has been recorded, generally in very low numbers, on more than 50 sites. Egg counts during the winter have shown it to be more widespread than once thought, being found in low densities along many suitable hedgerows in south/south-west England for example. Although not significant, there is a suggestion in the data that numbers have increased since 1976. Some of this increase may be due to an increase in recording effort following the discovery of its greater distribution. However, it is suggested that it's distribution has also increased, possibly as a result of more appropriate hedgerow management with agri-environment schemes for example, and so this increase is likely to be a reflection of this. More recently there has been a decline on monitored sites which most likely reflects a run of years with poor weather during the flight period of this late summer species.
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, Brown Hairstreak has been recorded from 128 transects in the Butterfly Monitoring Scheme. Of these, annual indices of abundance have been calculated from 75 sites, with an average index of 1 individuals per site.
For 25 of these sites, Brown Hairstreak has been recorded well enough to calculate annual indices of abundance in more years, allowing trends to be calculated.
In 2016, 35 individuals were recorded from 13 sites, producing annual indices at 11 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 (4)|
|Stable sites (13)|
|Increasing sites (2)|
|Declining sites (4)|