Hampshire and Isle of Wight Butterfly and Moth Society
Hampshire and Isle of Wight Butterfly and Moth Society
| Family: | Lycaenidae |
| Subfamily: | Polyommatinae |
| Genus: | Polyommatus |
| Species: | coridon |
| Authority: | (Poda, 1761) |
As its name suggests, the Chalk Hill Blue is found on chalk downland, although limestone downland is also used. The adult butterfly is most-often seen in bright sunshine, where the ground may appear to shimmer with the activity of hundreds, if not thousands, of males searching for a mate just a few inches above the ground. The distribution of this species follows the distribution of Horseshoe Vetch which, in turn, follows the distribution of chalk and limestone grassland. This species is therefore restricted to England, south east of a line running from West Gloucestershire in the west and Cambridgeshire in the east. This species is absent from most of central England, northern England, Scotland, Wales, Ireland, the Isle of Man and the Channel Islands.
| #Individuals | #Tetrads | 2022 | 2023 | Abundance Trend | 2022 | 2023 | Distribution Trend |
|---|---|---|---|---|---|
| 54842 | 15155 | -72% | 80 | 61 | -23% |
| #Records | #Individuals | Earliest Record | Latest Record | |
|---|---|---|---|---|
| All Records | 24,020 | 630,983 | 17/06/1990 | 31/10/2011 |
| 2023 | 1,019 | 15,155 | 29/6/2023 | 29/9/2023 |
| Location | Date | Quantity | |
|---|---|---|---|
| Earliest Record | Brading Down LNR 2 transect: Section 4 | 29/6/2023 | 1 |
| Latest Record | Mottistone Down transect: Section 4 | 29/9/2023 | 1 |
| Highest Count | Compton Farm | 15/7/2023 | 999 |
One of the issues with 'raw' trend data is that there is inherent bias based on the number of recorders. For example, the number of individuals and populated tetrads recorded are likely to increase if there is an increase in the number of recorders. In order to remove this bias, the normalised trends use data that has been recalculated using the average number of recorders over the trend period. This normalisation gives a much better picture of the true trends.
Average #Recorders: 80.12
Average #Recorders: 80.12