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'High' On Heyshott

For me, today was the best day yet in 2011. As BC Regional Officer Dan Hoare and I chatted on the steep climb up Heyshott Escarpment, we could see the bonfire smoke rising through the trees, and the sun was just beginning to burn through the thin cloud. We joined up with an enthusiastic mix of Murray Downland Trust and BC volunteers to open up an area of overgrown hazel coppice on the lower slopes of the reserve. This will act as a habitat corridor to encourage the movement of Duke of Burgundy from the more exposed old chalk workings higher up the reserve, down into the lower wooded areas. The Murray Downland Trust manages this reserve superbly - having ecologist Mike Edwards on the team does help! We've been working on this site specifically for the benefit of Dukes for a few years now, and last season they went bonkers. Maximum daily counts of 2s and 3s gave way to 7s and 8s, before suddenly increasing to 51 last May. Looking at the work-in-progress I'm confident that these numbers will increase again - perhaps significantly.
John & Trisha Murray, Naomi Barnett, Mike Edwards, Rowan Edwards, Mike Snelling, Roger Martin, Robin (Brinsbury College), Mike Hadley and Dan Hoare enjoying a well-earned break.
The Dukes will like this.

Once the work was done, Dan and I couldn't resist climbing further up the slope to enjoy the views here. In only ten weeks time these humps and hollows will be home to numerous Dukes, Dingy Skippers, Grizzled Skippers and Green Hairstreaks. As we sat looking out over West Sussex, with buzzards wheeling overhead, I got the first feelings that spring is not far off now.

Neil
Thanks for the memories

My visit to Heyshott was one of the best days of the year. The work you and your colleagues have done up there is admirable.

Thanks

Hi Neil,

Sorry to clutter your blog up. A quick couple of questions if it's ok. I'm planning a trip to Sussex in May, hopefully around the 12th, 13th and 14th. To be honest, I'm specifically coming down for the Duke. Assuming spring isn't early or late (say average lol!), when does the Duke start to emerge on Heyshott Down? Heyshott is one of the sites I have highlighted, but is it necessarily one of the best places to see him? We hope to stay at Arundel or close by. Any help or information would be much appreciated.

Best regards

Pete Simpson

Thanks Roger - the best is yet to come, so I hope you can visit again some time. I think you're on hols this spring, but by next year the numbers should be very good indeed.

Pete - yes, your timing will be perfect, irrespective of it being an early/average/late year. Those dates will ensure success, but spring temperatures will determine if this is peak or pre-peak time. Heyshott is suddenly a very good place to see Dukes! Feel free to PM me nearer the time. I'm out surveying Dukes every day that the sun shines during the flight season and if any (proper) work comes in, it gets done in the dead of night if necessary. So I should be out-and-about and able to hook up with you. Good timing for PBF locally too.

Neil

Neil
WE are back in UK for Mayday - so I shall probably be at Heyshott the following weekend.
Be good to meet up again......

Hi Roger,
Sounds like a good idea to me! Here's a table of dates/abundances from last year to assist with planning.
May 12th – 7
May 14th – 10
May 15th – 9
May 17th – 12
May 18th – 8
May 20th – 27
May 21st - 51
Heyshott is a 'late' venue (steep, north-facing slope) and 2010 was a 'late' year.
Neil

I presume that in the same way that plants need a crucial temperature for growth to commence, butterflies do not really develop until certain temperature levels are reached. So whether it’s cold or VERY cold in December and January makes little difference. I suspect though that February is a critical month as temperatures can easily be high enough in some years to trigger development whereas in other years, it remains too cold.

Locally in the Cambs/Herts/Essex area temperatures so far this February are running at about 3°C above long term average. These figures are more representative of an average March. I haven’t looked at data for other parts of the country, but I suspect there would be similar anomalies. The signs are that we will remain in a generally westerly regime until the end of the month so that implies above average temperatures will continue for a few more days at least.

Of course, March might well be bitterly cold. But it this recent spell of milder than average weather does continue, then we could be in for an early butterfly season.

Jack

Hi Neil,

Many thanks for replying. I'll take you up on that offer to meet up. Really appreciated. I'll send you a pm with the exact dates nearer the time (say mid-Aprilish). Yes, would like to see PBF aswell on the visit.

Regards

Pete

Great pics and great work, Neil. Can't wait to get back there myself.

Hi Jack,
As you say, late winter temperatures will not have much influence on emergence dates (from pupae) in the spring. However, prolonged cold through the spring (March, particularly April, and even early May) will have a significant influence on the rate of pupal maturation, leading to delayed emergence. This was very marked in 2010. In West Sussex the first Green Hairstreak emerged on an 'average' date of 13th April, but over the following weeks the number of observed adults remained extremely low. On 13th May the long-prevalent northerly winds (responsible for unseasonably cold nights until this point) turned to the SW, with a consequent rapid rise in temperatures. The next few days saw a real avalanche of emergences, both of Green Hairstreaks (dozens appeared 'overnight') and other spring species. A one month separation between first sighting and first significant numbers is a reflection of the unusually (for recent years) cold and prolonged spring.
Neil

Neil, if there is a late frost or other unusual weather prior to the Dukes' emergence do they suffer from abberations in the same way that white admiral and silver washed fritillary do?

Hi Susie,

Yes quite possibly, but the frost would have to be very late in the year, i.e. July/August cusp or thereabouts when the larvae are pupating. A late Spring frost would have no impact upon the emergent insect in this respect.

Felix.

The question:
Is it the temperature just AFTER pupation or just BEFORE emergence of adult that can give rise to aberrations? Most likely the former but it is possible that even both scenarios could have an effect.

Jack

Hi Jack,

'Tis in the last 24 hours of larval stage and the first 48 hours of pupal stage (or there abouts) that the insect is susceptible to such triggers. It has long been known that extreme shocks of either heat or cold during the last 24 hours of the larval stage and the first 48 hours of the pupal stage can disrupt the natural process of metamorphosis and inhibit or disrupt the processes in which organic chemicals create the colouration of the wing scales. Much work has been carried out around this subject and countless experiments have been performed on many species.

The extremes of temperature required for such aberrations to form however are right on the cusp of what would be fatal to the insect. Hence these types of aberrations are scarce. There are exceptions however, and certain species (such as the purple emperor) are particularly susceptible to producing aberrant forms induced by temperature shock, indicating that aberration occurs at a lower temperature (or higher temperature when considering cold-shock) than would generally considered to be fatal.

Aberration in purple emperors is actually quite common; which can be evidenced in the amount of aberrations seen in any particular year as a percentage of actual adult butterflies observed.

Felix.

Hi Susie,

Most of these environmentally-induced aberrants, including the numerous White Admirals, SWF, Comma etc seen at Southwater Woods, appear to be caused by large diurnal temperature swings (warm days and cold nights) during the period of pupation and very early pupal development (late May to mid June). Dukes pupate quite late in the 'preceding' summer (late July and August), when temperatures are relatively stable and diurnal ranges are quite low. They are therefore less likely to be affected in this manner.

Aberrant forms of Duke of Burgundy are quite rare, apart from ab. gracilens, and all the 'abs' that I have personal experience of are genetically controlled. This includes the rare ab. leucodes shown below. Leucodes appears at first sight to be a very faded, almost sun-bleached individual, but the patterning over the proximal area of the hind wings and colour of the thoracic hairs are a give-away. Within the limits of natural variation, many males within woodland (cf scrubby grassland) populations are noticeably 'dark'. However, I'm sure that some of the dark 'abs' recorded in the past are environmentally-induced, due to the conditions outlined above occurring unusually late in the year.

Neil

Hi Felix,
That's not the first time you've been quicker on the keyboards than me. I must improve my words-per-minute.
Neil

Sussex Kipper wrote: I'm sure that some of the dark 'abs' recorded in the past are environmentally-induced, due to the conditions outlined above occurring unusually late in the year.

Quite possibly, although it's worth mentioning that some colonies produce 'dark' individuals on a regular basis, with 'dark' individuals being the norm in the population. Such specimens have greatly reduced areas of orange markings (particularly in the males where the hindwings are pretty much totally dark with the exception of the fringe and the marginal markings.

Felix.

What is it about Southwater Woods?

I suspect that the culprit in this locality is high temperatures rather than low temperatures. Both extremes (ie day/night 'swings') are not required.

High temperatures produce a certain kaleidoscope of aberrations and low temperatures produce others. In some species (white admiral ab.nigrina for example) the same aberrations are produced at both ends of the temperature spectrum.

There are plenty of other SWF populations that are more likely to be in late frost pockets than Southwater, and yet do not have a history of spewing out rare 'thermo-abs'.

Light deprivation throughout the larval stage also induces aberrant forms in the adult insect, as does an atmosphere unnaturally rich in oxygen.

Could it be just the relative topography of Southwater Woods that provides the excessively warm microclimate required? or perhaps something to do with the metalled roads within the woodland complex pushing the ambient temperature at ground level within the woodland up just that tiny fraction of a degree that makes all the difference?

Felix.

Ps. Sorry for the

Horsham Natural History Society

On Monday (21st February) I gave a talk to a sizeable audience of Horsham Natural History Society members, about the 'Private Life of the Purple Emperor'. Judging by the avalanche of good questions at the end, I'm pleased to say that most must have stayed awake, while I indulged in one of my favourite topics for an hour. It was nice to see Susie in the crowd, and I received a generous £50 donation towards our conservation 'fighting fund'. I couldn't have asked for a friendlier audience.

Hi Felix,

I wish I knew the 'secret' of Southwater Woods, but there must be something affecting the local microclimate here. The area is relatively 'high' wrt the surrounding landscape, there aren't many metalled tracks through the complex and emergence dates for WA and SWF are not 'early' here, so I suspect it chills. It would make a fascinating study for someone - I wish I had the time! It would be very interesting to track down a local amateur meteorologist and get some hard data.

As you say... it only takes a minor temperature anomaly to do the job. PBF emergence dates within a sloping woodland complex such as Rewell Wood can vary by up to 10 days, dependent upon elevation differences, within 1 Km.

Neil