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Chalk-hill Blue (Polyommatus (Lysandra) coridon)
© Nick Greatorex-Davies
The Chalkhill Blue, as its name suggests, is restricted to chalk and limestone grassland where its foodplant Horseshoe Vetch (Hippocrepis comosa) grows. Though still widespread in these habitats it is far less common than it once was because of the destruction of herb-rich calcareous grassland due to agricultural intensification. (For further details on this species see http://www.butterfly-conservation.org/).
Family: Lycaenidae
Status: Rapid increase
Status details:
Status since 1976 is Rapid increase with an increase of 42.8%
Status over the last 20 years is Stable with an increase of 11.6%
Status over the last 10 years is Stable with an increase of 9.9%
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 butterfly has shown big fluctuations in its all-sites index over the monitoring period. During the seven year period 1990 to 1996 the index increased to an all-time high in 1996. Since then the index has declined substantially to well below average. Indices are calculated from relatively few sites, as reflected by the size of the standard error bars on the graph and so need to be treated with caution. A similar number of sites have shown increases as decreases. The decline at Fontmell Down has been particularly dramatic. Data also indicate that populations on some sites have remained more or less stable. Because the data show mixed results changes probably largely reflect the local management of sites.
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, Chalk-hill Blue has been recorded from 323 transects in the Butterfly Monitoring Scheme. Of these, annual indices of abundance have been calculated from 295 sites, with an average index of 164 individuals per site.
For 133 of these sites, Chalk-hill Blue has been recorded well enough to calculate annual indices of abundance in 6 or more years, allowing trends to be calculated.
In 2006, 43473 individuals were recorded from 125 sites, producing annual indices at 101 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
• Colonised sites (3)
- Stable sites (64)
- Declining sites (14)
- Increasing sites (24)
