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Elderly residents of the Holtspur area, between High Wycombe and Beaconsfield,
have told us that they recall seeing Chalkhill Blue butterflies in the Holtspur Valley. Unfortunately,
there were no written records of it ever having been seen there and modern surveys had failed to detect
it. However, this is a highly mobile species. The males (at least) are recorded well away from any known
colony every year.
So when we pushed back topsoil to make a feature called a 'scrape' (in winter 2003/4) in addition
to planting Kidney Vetch (to improve conditions for the scarce Small Blue which was sporadically
present on the reserve) we planted Horseshoe Vetch, the foodplant of the larvae of Chalkhill Blue.
We hoped that some vagrants of both species would wander back.
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Chalkhill Blue pair
Photo © Nick Bowles
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Horseshoe Vetch
Photo © Nick Bowles
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Horseshoe Vetch is the only known food plant of the Chalkhill Blue.
Which is a shame in more ways than one; it is relatively hard to grow, expensive to buy and disappears
from both overgrazed meadows and meadows that suffer grazing neglect. Even so, we committed to create
sufficient habitat to support a viable colony of the butterfly, over a number of years.
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The first scrape was an evident success in terms of the amount
of vetch that flowered within 4 years of us planting tiny plants into the bare sub-soil that we
had exposed. Our studies of the Chalkhill Blue, however, suggested that a single large area of
vetch would be less successful than several adjacent areas of vetch. So a second scrape, backed
on the 'up-hill' side by a low bank of spoil, was put in during the winter 08/09.
This second feature was positioned where the chalk was deeper beneath the
top soil, so we had to plant into a thin layer of topsoil rather than sub-soil. We had some
concerns that the Horseshoe Vetch would thrive here as it had in the first position. Luckily,
it seems to be coping well, but we will need to keep the area relatively clear of other rampant
vegetation for some years before it can 'look after itself'.
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Our first scrape exposed bedrock chalk,
which suits vetches better than grasses.
The yellow flowers of the vetches are obvious.
Photo © Nick Bowles
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There have been other beneficiaries of the second
scrape, like this scarce arable weed, Round-leaved Fluellen.
Photo © Nick Bowles
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Spring 2011 was really helpful to butterflies and moths.
One result was early flight periods in June and July, with dispersal of many species away from
larger colonies. This benefitted several species and in August we received news that a male
Chalkhill had been seen at Holtspur Bottom. Small groups of would-be observers were soon to
confirm that this wasn't a single vagrant male but several butterflies. Both sexes were seen
and eventually a female was observed egg-laying.
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The return of the Chalkhill Blue is very welcome. However, the true measure of the reserve's
successful management will be if we can maintain a colony here into the future. There will need
to be work to see that the amounts of Horseshoe Vetch continue to increase, probably through
planting small amounts every year, but hopefully through natural self-seeding. Probably though
the creation and 'plug' planting of further scrapes, as the existing scrapes slowly succumb to
denser vegetation, which outcompete the butterflies' foodplants.
We shall also survey the local area to see if other colonies are hiding, undiscovered nearby.
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Part of the Holtspur volunteer team erect
temporary fencing to protect essential
vetch foodplants from sheep.
Photo © Nick Bowles
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