Thursday, 20 March 2014

On tissues and brimstone butterflies...

Following the circulation of the recent newsletter that included a note on Mat Ridley`s monitoring of the tissue moth in a cave near his home at Carmel, Steve Lucas sent me an email. Steve is heavily involved with bat survey and conservation and, with appropriate licences, visits caves to monitor the bats present. It is also well to remember that it is illegal to deliberately disturb hibernating bats and to be aware that prolonged presence of people may modify cave temperatures, to the detriment of hibernating bats.
Steve has previously told me of recently finding a hibernating tissue moth in a cave at Pumpsaint and, this week, he told me of yet another find, this time in Ogof Pasg, a limestone cave on the north-facing slopes of Mynydd Du. Here he saw two tissues (and many heralds) on 5th January 2014. The tissue moth is rare in Carmarthenshire, with only a few records - from Pembrey (Jon Baker and myself), Tregyb Woods near Llandeilo (another Steve Lucas record), from  Rhandirmwyn and, of course, Mat Ridley`s from Carmel. There has been the suggestion that the Rhandirmwyn records are incorrect, but I have personally found - albeit sparingly- the food plant alder buckthorn growing  in the hedgerows in the Rhandirmwyn-Cilycwm area. As a consequence, to me, there is logical validity in these tissue records as, morphologically, any preserved Rothamsted specimens ought to be not difficult to identify. Whilst we know that there were certainly incorrect determinations with at least some of the later SN74 Rothamsted moth data (in particular the latter years), there may be the danger of `throwing out the baby with the bathwater`, unless a full consideration of the surrounding habitat and other factors are made when addressing the veracity of the Rothamsted SN74 data.
At the Ogof Pasg site, the tissues will have had to make an uphill journey of at least a kilometre, over bare moorland, to reach the hibernation cave - how do they find it? Possibly, it may even have been used for generations of tissue moths. They also use empty old buildings elsewhere in Britain and possibly in Carmarthenshire too. Are the Pembrey tissues using the mostly now secured (for bats), old munition bunkers at the former Royal Ordnance Factory (now the Country Park)?
The food plants of the tissue caterpillars are alder buckthorn and purging buckthorn. The former shrub is very scarce in Carmarthenshire, whilst the purging buckthorn is very rare - virtually only found on the Carboniferous limestone, plus a few plantings elsewhere. They are easily overlooked (unless you`ve `got your eye in`) but I suspect that alder buckthorn at least, is scattered and mostly unfound, in hedgerows on the Coalfield in the SE, but also on the Siluro-Ordovician rocks on each side of the Tywi anticline. It also probably occurs on the base-rich damp areas of the Old Red Sandstone.
The distribution of the brimstone butterfly (which has the same larval food-plants as the tissue) is mostly concentrated in the SE of Carmarthenshire but this is partially (but not entirely) due to `observer bias` - myself, Barry Stewart, Richard Pryce et al). A map that I collated almost twenty years ago (in 1995, and prepared by RD Pryce) is shown below and this certainly demonstrates the stronghold in the south-east of the county. In this particular area, it has been helped by deliberate plantings of alder buckthorn on urban-edge habitats, at WWT Penclacwydd near Llanelli (hence the good numbers annually seen there), and other localities. Barry Stewart observed, many years ago, that the `local brimstones` at Penclacwydd preferred alder buckthorn over purging buckthorn for ovipositing.

Missing from the map are some subsequent brimstone records - from Halfway near Llandovery, from elsewhere in the upper Tywi Valley and a record by Moth Group member Steve Clarke at Cwm-llwyd on the northern flank of Mynydd Du. There are probably also other later records that I`ve forgotten about.

 Above: late summer brood brimstone at Tyrwaun, Pwll.

3 comments:

  1. Two comments adding to your argument, Ian: 1) a Brimstone butterfly in the Cothi valley just south of Brechfa last summer, SN53 so well north of your map; 2) two records of Tissue at Dingestow Court, Monmouthshire where Alder Buckthorn is present but uncommon, both to lighted windows and neither in the regular 50+ Herald roost in the cellar there.

    Having said that, not all Rothamsted errors are misidentifications: some are inputting or miscoding errors eg where a different species was recorded but the code for Tissue was accidentally input instead. Even if there is a logic to accepting NE Carms Tissues, the records are not necessarily acceptable. Jon pended records until a pattern was established, but the problem is a lack of recorders at Rhandirmwyn now to establish that pattern.

    Maybe Isabel will settle things by catching a Tissue at Cilycwm this year.

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  2. I later recalled another brimstone record away from the `SE Coalfield area` - one seen by Julian Friese near Ffairfach, Llandeilo in c1998.
    Regarding the comments about the tissue moth in NE Carms ie the `Rhandirmwyn Rothamsted records`, I was unaware that any Rothamsted errors were due to inputting issues and had assumed that they were mis-identifications of preserved specimens in alcohol (or whatever they are preserved in).The tissue, due to its size and crenulated wing edges should be relatively easy to i/d. I either read, or was told, that due to cutbacks and staff changes at Rothamsted, the quality of data had diminished in later years. In support of what Sam is saying, I now have seen the number recorded of tissue records coming from the SN74 trap (c 18 or so) which, I feel, is excessive for a scarce, `thin-on-the-ground` moth - thus suggesting an error. A low number would be more plausible.
    The SN74 Rothamsted trap data has been discussed by myself, Sam and Jon over the years, and it really is a problem. There are records of scarce moths in that data source that appear to be `logical` given the habitat etc, yet it is spoilt by `difficult to sort` out errors. Jon`s approach of isolating the Rothamsted data from the main Carms database has to be the best approach and, at a later stage (perhaps when we have a better picture of the N Carms upland moth fauna), we can carefully, and with consensus, try to extract certain records that are plausible (especially those that are supported by seperate 1970s RSPB recording data from Gwenffrwd-Dinas).
    It is a great shame that this Rothamsted SN74 data is contaminated (to use Jon`s phrase), as the person who actually operated the trap (the late Dafydd Davies) is beyond reproach, as he was a careful recorder of natural history. It also leads to the thought that -unless there was the almost impossible scenario that the SN74 data was alone in being partially inaccurate- that much the UK Rothamsted data has the same problem.

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  3. 14+ Brimstones at WWT today - the most I've ever seen at this time of year there - or ever possibly?

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