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THE
MOUNTAIN RINGLET IN CUMBRIA |
| The Mountain Ringlet Erebia epiphron is a speciality of the Lake District, this being the only place in England and Wales where it occurs. It is an enigmatic species, living on the high fells but only flying in sunshine! Its larval foodplant, Matt Grass, is everywhere, but the butterfly is found only in specific areas, apparently linked to the geology, soil type and possibly aspect. Don't believe everything you read in butterfly books about this species; this webpage is based on local knowledge and the efforts of members of Butterfly Conservation's Cumbria branch, who monitor the fells. One esteemed text, recently re-issued, quotes "evidence" that, because of global warming, a third of colonies have become extinct and on average other colonies have moved 140 metres higher up the fells. Apart from the fact that this would mean that most colonies were now on the very summits, which are usually avoided, there is actually no evidence, based on observation, that the species is in anyway declining in Cumbria. In fact, survey results from 2010 are very healthy, but that may only mean that a lot of effort was expended searching for this difficult species and the weather was reasonably favourable. The research quoted above was apparently based on surveys of sites in the last three weeks of July, as that is when the books say the species usually flies. In Scotland perhaps, but in Cumbria you will only find the tail-end stragglers by then (see below). Furthermore, the weather is crucial when conducting surveys. Two visits in 2010 to the same site, two days apart, yielded counts of 200+ and 5, the former when it was sunny the latter when largely cloudy! On one day you might conclude from casual surveys that the species was thriving, on the other that it was in difficulty! Just to show how difficult it is to monitor this species consider the following. Derek Ratcliffe in his New Naturalist book "Lakeland" wrote in 2002 of this species: "In good years it spreads from the main colonies at 455-760 metres, descending to lower levels (120 metres at Wasdale), but does not colonise new ground permanently. In 1977 I found a single female at 215 metres behind Patterdale, presumably from St. Sunday Crag above, yet over miles of Nardus grasslands on Helvellyn that day, I saw no more". I don't know of any records from St. Sunday Crag itself but years later, in 1993, several Mountain Ringlets were found on Arnison Crag just behind Patterdale. This is the most likely source of Derek's specimen and the species had probably been breeding in that area for all of those sixteen years, unknown to anyone. Another seventeen years passed before a breeding site was confirmed from this area! In 2010 there was no sign of the species on Arnison Crag, despite extensive searching, but further up the ridge that day there were large numbers on Birks. So it's only taken 33 years since Derek's first observation to get an established record of this site....which is why monitoring the species is so difficult! How many more such sites are there in the Eastern Fells? There is no doubt that it does spread out during the flight period in good or even most years, which is why records of ones and two's are of little value in monitoring the distribution of this species. But we are now fairly sure that breeding sites do move and absolutely certain that it breeds as low as 200 metres (see below). Breeding sites show a marked preference for the west and south-west of the region, especially around Wasdale, the Langdales and Honister where numbers have traditionally been highest and are holding up well. Colonies to the east, around Helvellyn, Haweswater and Kirkstone, are fewer in number and more isolated, although some are very strong. The Red Screes site, where the species was first discovered in Britain in the early 1800's, now appears to be weak, but new breeding sites have been found close by, one as recently as 2010. The species does appear to move about (sometimes downhill!), for reasons we don't yet understand. This is another reason why it is difficult to assess population changes; one site may become extinct but there may be two new ones nearby in some less accessible place that we don't know about! Mountain Ringlets may be found in the Lakes between the beginning of June and mid-July, but at one low level site emergence sometimes occurs before the end of May! However, numbers peak for most colonies around the last two weeks of June, followed by a fairly long tail when only small numbers tend to be found. Analysis of breeding records (i.e. sites where significant numbers have been recorded) over the last ten years gives a distribution:
This is a frustrating species for the casual observer to plan to see and why records over the years are relatively sparse, despite the increasing popularity of fell-walking! If you want to see the species, I'd suggest you pick the day in the last fortnight of June that has the best weather forecast promising long periods of sunshine with temperatures above 17 C at 500 metres!!! Try Hartsop Dodd, Kidsty Pike, Raise, Cold Pike/Little Stand, Brandreth or the Irton Fell/Illgill Head ridge rather than sites suggested in the books. Breeding sites are normally found between 550 metres and 700 metres (to set that in context, the very highest peaks in Cumbria are just over 900 metres). However, we know they can thrive at 250m just as well as at 650m if the conditions are right – we just don’t know what those conditions are yet!
In spite of its preference for altitude the species does avoid the summit tops, as it is nearly always found in sheltered spots or flushes at the base of crags. Matt Grass, its larval food plant, occurs in every 2 km square of the Lakes. BUT there have been no records ever from some fells (although well walked) such as Great Gable, Bowfell and the Band, The Fairfield Horseshoe, and Skiddaw, despite the abundance of Matt Grass throughout. The species is very strong just to the north of the Wrynose Pass, but curiously has never crossed the road to the Coniston range! Plants on which the Mountain Ringlet nectars, such as Thyme, Tormentil and Meadow Buttercup, tend to be found at the base of crags and gullies, where mineral enrichment occurs. They are virtually absent on the summit tops, making this another reason why the species is unlikely to move higher in the Lakes. There appears to be a very strong geological link to its habitat requirements (see map below). Known sites are found only on certain of the igneous Borrowdale Volcanic rocks - the Skiddaw and Silurian Slates to the north and south respectively have no colonies. It may be that the areas avoided, being more acidic, are mineral deficient (especially in calcium). Matt Grass is so lacking in mineral nutrition that even the sheep leave it alone (which is why it becomes dominant if the fells are over-grazed).
Indeed, the colonies in the west of the Lake District could all be considered to be one super-colony as they are all inter-connected by the ridges that radiate out from the central dome of the Scafells. Any interchange that does occur here will enable genetic mixing and strengthen future generations. It may be the case that colonies in the east have a different genetic make up and, being more isolated, could decline through lack of genetic mixing. On the other hand it may be the case that this area is under-recorded and there may be more inter-linking sites than we know about at present! Within a colony there are genetic differences of size, brightness and number of spots. English specimens differ slightly from those of Scotland, which differ again from European specimens. There has been much speculation about the potential loss of an alpine species like the Mountain Ringlet as global warming occurs. It is just speculation, as so little is known about the habitat requirements and ecology of this species. The site that always features the earliest emergence (Irton Fell) is the one found at lowest altitude (200-250m) and is on the milder west coast, where it enjoys the benefits of warm Gulf Steam air and higher humidity - just the sort of conditions Global warming is supposed to bring. This colony has been observed for over 60 years, with little apparent change in strength, even in recent years. On the other hand, despite global warming, we have just had one of the hardest winters for sixty years - snow covered the fells continuously for five months in 2009-10 and numbers of Mountain Ringlets recorded in 2010 did seem to be good, but this may only be the result of more determined monitoring. Flight times were not noticeably different in 2010, perhaps because the months between April and June enjoyed dry sunny weather just at the time larvae were developing and pupating. Could it be that the amount of snow cover is important? At low altitudes this protective cover is not present and appears not to be needed. At high altitude it may be beneficial, in which case the species may well benefit from moving to higher ground in Scotland, but this is not possible in the Lake District. It's such a complex picture. To throw another spanner in the works, many pupae are devoured by Field Voles, a species notorious for rapid fluctautions in numbers from year to year even without hard winters! Any effects of global warming will manifest themselves in changes in the habitat, but we need to understand the precise habitat requirements of this species before we can assess what changes are taking place! Butterfly Conservation Cumbria branch is working hard to try to understand those requirements. All in all, the Lake District Mountain Ringlets are a fascinating and unsolved enigma! If you have any comments on the above theories please get in touch. If you are walking in the Lake District in June or early July please look carefully and report any sightings via this website.
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