Thursday 8 June 2017

Black Hairstreaks 7th June 2017

There are five species of hairstreak butterfly that inhabit Britain and the rarest of them is the Black Hairstreak, with many enthusiasts travelling long distances to see them during their very short flying season.

I am fortunate that I live in Oxfordshire which is one of the strongholds of this butterfly in its very restricted range. They are only found in a string of ancient woodlands, relics of a once continuous forest that extended from Northamptonshire in the north, southwards through Cambridgeshire, Huntingdon, Buckinghamshire and Oxfordshire. The reason they are so restricted is that they do not disperse widely as they are very reluctant to fly any distance and it was only in the former extesnive forest that the continuous history of traditional woodland management  proved beneficial to Black Hairstreaks. This traditional form of management ceased around the end of the 19th century and as a consequence many colonies of this small butterfly died out but since then conservation efforts in the fragmented remains of the forest, especially in Buckinghamshire and Oxfordshire by BBOWT (Berks, Bucks and Oxon Wildlife Trust), have enabled the Black Hairstreak to increase and thrive although there is now a new threat caused by the burgeoning deer population browsing their foodplant, Blackthorn.

When the M40 was constructed through Oxfordshire some twenty years ago, an area of several hectares called the M40 Compensation Area abutting Bernwood Forest was created specifically for Black Hairstreaks. It was highly successful and a very large colony of Black Hairstreaks has now become established there. On recent annual visits I can recall seeing double figures of this enigmatic butterfly nectaring on a Wild Privet bush within metres of the forever busy and noisy Motorway. However, as of this year I can now no longer go there as the whole area has been 'deer fenced' to protect it from deer, as their browsing was degrading the habitat. For the greater good I am content to suffer this inconvenience and after all is said and done there are plenty of other areas nearby to seek out Black Hairstreaks, as evidenced below.

Black Hairstreak colonies are usually small, consisting of no more than a few dozen individuals but after a warm Spring such as this one numbers can be considerably more, and conversely, less after a wet, cold Spring. The colonies are often  restricted to a small, favoured part of a wood such as a sunny glade or ride with plentiful amounts of unshaded Blackthorn growing along sheltered edges of woodland and with Bramble, Dog Rose and Wild Privet flowers for the butterfly to nectar on. Fortunately this habitat is not in short supply in Oxfordshire and Buckinghamshire 

The first individuals are on the wing from about the first week in June onwards, give or take a few days, but the adults are only on the wing for a very short time and usually have gone by the first week in July. They are elusive, spending much time in the canopy of higher trees feeding on aphid honeydew, sometimes hardly ever descending lower but if you are lucky and patient they can be found, having flown down to nectar on their chosen flowers and then are very tame and approachable, so much so you can, with a little patience get them to walk onto your finger. Believe me I have done it!

Black Hairstreaks are not black but are brown and in fact they are quite plain.The upperwings are dark brown with small orange bands at the edge of the wings, more prominent on females.The underwings are a paler mouse brown with a broad orange band on the lower hindwing and a row of black and white spots along the inner edge of the orange band.The distinctive white 'hairstreak' runs across both underwings.

Black Hairstreak

So it was that today Peter and myself rendezvoused at a suitable wood with copious amounts of Blackthorn growing at its edges along the aforementioned sunny sheltered rides, the Blackthorn interspersed with the hairstreak's three nectaring plants. 

I was glad to be looking for Black Hairstreaks today as it is best to get out early in the hairstreak's short flying season in order to see them when they are newly emerged and are less likely to be showing signs of wear and tear. One also has to remember our capricious weather and that opportunities to see them flying can, and frequently are, limited by adverse weather.

The forecast for today was sunny spells but when we met at ten am it looked anything but, with much grey cloud, a gusting wind and little sign of sunshine. Undeterred we walked towards the wood and took a small ride to our right, bordered on each side with large mature Blackthorns, that wound its way into the green recesses of the wood, 

Black Hairstreak habitat
We came to a suitable patch of Bramble and stood by its delicately tinged pink flowers and looked but there was not a sign of any butterflies let alone a Black Hairstreak. Slowly though, the cloud was breaking up and occasional brief interludes of sunshine illuminated the Blackthorn. We split up with myself standing by the Bramble patch waiting, more in hope than expectation, for a hairstreak to fly down to nectar on the Bramble flowers whilst Peter walked on further to see if there were any other suitable patches of Bramble where a hairstreak might be found.

Ten, maybe fifteen minutes passed and I heard a vague cry from a now distant Peter. This could only mean he had found our quarry and I hastened up the track, the long lush grass brushing my trousers and taking care not to  crush the numerous Common Spotted Orchids, their pale purple flower spikes like so many church spires in the grass.

Common Spotted Orchid
I turned a corner and there was Peter photographing a Black Hairstreak nectaring on a generous patch of Bramble flowers. the familiar little triangle of closed brown wings was clearly visible as it delicately wandered over the petals with its proboscis between its legs, lapping up the nectar from the flowers. It was here for about five minutes but the occasional gust of wind made it flustered and it would flutter about before settling again but always moving higher before finally jinking its way up and over a Hazel tree standing behind the Bramble.

Black Hairstreak
Neither of us were truly satisfied with this brief view and decided to wait and see if it or another came back. It was not unpleasant now, as the sun was more continuous and it was quiet and secluded with just the two of us standing in the ride.The sunshine had brought out other butterflies too and we were visited by Red Admirals, Speckled Woods and I saw my first Large Skippers for this year.

Red Admiral

Speckled Wood

Large Skipper
After a while, and a little bored I walked twenty or so metres back down the ride to check another Bramble patch but was unsuccessful in finding any hairstreaks. I did however notice an area of slightly trampled grass below the Blackthorn and looked closer. Initially I could see no reason for anyone being interested in this part of the Blackthorn hedge but by chance the night before I had seen an image of a Black Hairstreak Chrysalis, which is a marvel of camouflage, looking just like a tiny bird dropping and is usually placed on a Blackthorn leaf or stem.

I looked closer, at first seeing nothing untoward. But then, yes, there right before me, on a shiny Blackthorn leaf was a tiny dark lump with a white mark at its centre. It was a Black Hairstreak Chrysalis. I was overjoyed  as this was a great find and something I had never seen before nor ever expected to find.  I called Peter and together we marvelled at this tiny vestige of the Black Hairstreak's life cycle. Reading up  about this I learnt that despite the superb camouflage many are predated especially by Willow Warblers!

We went back to the original Bramble clump to find the Black Hairstreak had returned or maybe it was another. We watched as it did pretty much what the previous one had done, nectaring on the Bramble flowers but again the gusting wind made it fidgety and like before it flew up and over the trees behind. Several more hairstreak visitations came and went before we decided we had enough.We estimated we had seen between three to five Black Hairstreaks but for me the great prize was finding the Chrysalis.

We visited another suitable area of habitat a short drive away where the main nectaring plant was Wild Privet and found another four Black Hairstreaks there, so maybe this is going to be a good year for them. I do hope so.

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