US social scientist Kenneth Boulding : ‘If you believe exponential growth can go on in a finite world, you are either a madman or an economist’.

Tuesday, 20 July 2010

20/7/10: Another new White-letter Hairstreak colony in Bexley

Following on from my White-letter Hairstreak butterfly find at Crayford Marshes (see 2/7/10 posting), late this afternoon I checked Barnehurst Golf Course for the presence of White-letter Hairstreak for the second time in a fortnight.

I had had a possible 4 sightings on 6th July, 3 along the fairly substantial strip of English Elm along the western margin of the site bordering Manor Way, and 1 at the eastern end parallel to Perry St, where there is another reasonable amount of Elm. All were briefly in flight and I could not see where they settled to get a proper view and confirm presence.

Today, besides a possible sighting at the Perry Street end, I obtained a definite identification by the Old Manor Way entrance at the west end of the site (TQ 506 760). I had been pondering the dearth of suitable nectar sources in the immediate area when I saw a small brown butterfly land on a cluster of the few Bramble flowers not yet setting fruit, just as I was about to exit the Golf Course and head for home. I swung my binoculars onto it just in case it wasn't another Gatekeeper, and because I'd seen a possible White-letter Hairstreak on an Elm 'bush' here two weeks ago. And lo, and behold, a W-LHS it was! Cue a bit of fist-pumping, but not too obviously in case any passers-by thought I was some kind of nutter ..... The insect was about 8' from me and only a few yards from gardens and houses on either side. The time was 18.17 and it was a warm, sunny afternoon with a slight breeze. The area where it was feeding was still getting some sun from the west at this time.

A White-letter Hairstreak was seen feeding on Bramble flowers here at the 'stub end' of Old Manor Way, by the entrance to Barnehurst Golf course, early this evening. Dead, ivy-clad Elm to the left, live Elm centre, Pedunculate Oak right. Swathe of Bramble, Stinging Nettle and Mugwort in the foreground.

A bit of subtle management to improve W-LHS habitat would probably be useful here. The Elm is reaching a decent height before succumbing, but there is relatively little coming through in the way of mid-height (or even small) suckers. This is because a considerable number of dead Elm have been left in situ and are covered in Ivy, shading and swamping out new growth. Several medium-sized Sycamores are taking up space that Elm could colonise. And in one area a Russian Vine from a neighbouring garden is covering an increasingly large area within the Elm zone whilst a dense swathe of bordering nettles is hindering any Elm colonisation along the margins of its present extent.

At any rate, the fact that I've trebled the apparently 'known' number of W-LHS sites in the Borough in 2 weeks rather supports other people's theories that the species is under-recorded - it's not the sort of thing that one is necessarily going to find on the basis of a few cursory glances up at a bunch of Elm trees. Indeed the LNHS butterfly recorder tells me it has already shown a very large increase in records between the 1980s and 1990s - the second-highest of any butterfly species in London - which suggests better recording rather than a massive population increase and spread.

Elsewhere on the Golf Course today, Essex Skipper, Gatekeeper, Meadow Brown, Holly Blue, Small Copper and Red Admiral were seen. The usefulness of the oft-maligned Common Ragwort as a nectar source for several of these butterflies, at a time when not much else is available in such grassland, was especially evident.

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