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The Status of the Marsh Fritillary in Wales: 2017

Marsh Fritillary at Pembrey Forest, May 2017. Paul Gadsby

Signs of improvement…. After the very poor year for Marsh Fritillary in 2016 I’m sure those embarking on surveys for the butterfly both in the flight season and during subsequent larval web surveys/ monitoring in the autumn, did so with some trepidation as to what they might or might not find. Despite some extremes of weather during the flight period, the overall feeling was that the adult butterflies seemed to have fared better than in 2016. Did the Marsh Fritillary do better in 2017 and if so to what extent? Keep reading to find out……

Introduction

The conservation of the Marsh Fritillary, one of the most rapidly declining butterflies in Europe, hinges on knowing where our core populations are, how they are faring and making sure that sites are well managed for the butterfly. Where are they? – Population status surveys

To maintain an up-to-date picture of where our Welsh Marsh Fritillary populations are (distribution) Butterfly Conservation Wales (BCW) co-ordinates a Wales-wide programme of visits in which every population gets at least one survey visit every five years. As well as confirming presence or absence, these visits can also highlight concerns, such as management issues, that need following up. How strong are they? – Surveillance programme

To assess how strong our Marsh Fritillary populations are, and how this changes over time, the Wales Marsh Fritillary Surveillance Programme was established in 2012 by BCW in partnership

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with Natural Resources Wales (NRW). Annual larval web counts of key populations (21 currently) are undertaken and used to calculate both site-level and Wales-wide trends.

Population Status Surveys

The rolling programme of five-yearly site visits continued in 2017. Twelve sites were identified for survey which had no Marsh Fritillary records since 2012 or 2013. Nine of these sites were visited by BC Wales staff and volunteers, with support from staff at Natural Resources Wales (NRW). The remaining three sites had all been visited at least once since 2013, so were a lower priority for survey. Marsh Fritillary was recorded at five of the nine surveyed sites. The best count was 19 adults at Rhos Pwllygawnen SSSI in Carmarthenshire – a large site with plenty of excellent breeding habitat. The site was surveyed early in the flight season so peak numbers are likely to have been even higher. Further surveys are required at three of the sites which produced negative results, particularly at Park Farm (near Cross Hands) and Caeau Nantsais SSSI (in North Carmarthenshire) where surveys were done in less than ideal weather. Small populations could still be present at these sites; these are easily missed during a single visit. Other surveys

BC volunteers visited many of the well-known Marsh Fritillary sites in Wales, as well as some of the lesser-known ones. In addition, four new populations were discovered – in keeping with 2016 these were all in Carmarthenshire, mainly in the under-recorded north of the county. There was also some good news from Blaen Cib near Llandeilo (Carmarthenshire), where 13 larval webs were the first site records since 1996. At six populations Marsh Fritillary was recorded from breeding habitat located outside the known boundary – excellent news, as large sites are more viable in the long-term. Many of these additional areas of habitat were found during surveys in Carmarthenshire carried out by Richard Smith and other volunteers.

Marsh Fritillaries in 2017. Left: Adult female at Wallis Moor, Pembrokeshire (David Redhead). Right: A large larval web found in early October at Capel Isaac, Carmarthenshire (Richard Smith).

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Status overview

The 2017 sightings mean an addition of five populations and a ‘loss’ of three populations for the most recent five-year period (2013-2017). The ‘lost’ sites still support areas of breeding habitat and may be reoccupied in the future, or perhaps small populations are quietly hanging on at these sites undetected. The ‘net gain’ of two populations is good news in what was a pretty average year for the butterfly. It is likely that most of the recent gains are due to better recording effort rather than genuine site colonisations. Table 1 shows the change in status in the Welsh counties with resident Marsh Fritillary populations. Carmarthenshire continues to forge ahead with 41% of current populations; all of the new sites found in 2017 were in this county. Only 9% of Welsh populations are in the north of the country, where unfavourable land management continues to pose a serious threat to the butterfly. Action is urgently needed to secure the future of the Marsh Fritillary here. Table 1. Change in Marsh Fritillary population status in Welsh counties in 2017.

Plans for 2018 and beyond

We will continue to survey all current populations at least once every five years. Thirty-three sites have been identified for survey in 2018, of which 15 are a high priority for survey this year; these have no records of Marsh Fritillary since 2013 or 2014. Many of the lower priorities are sites with older records which haven’t been visited for some time, but which are still likely to support areas of breeding habitat (marshy grassland with Devil’s-bit Scabious present). The map on the following page shows the location of the priority survey sites. If you’d like to help out with surveys at a site near you, either during the adult flight season (late May – June) or the larval web survey season (late August – September) then we’d be delighted to hear from you. We can provide guidance, survey maps and in many cases we can help with access permissions too. Contact details for getting in touch are provided at the end of this newsletter.

Vice

CountyCounty

2012-2016

colonies

2013-2017

coloniesNew sites Rediscoveries Sites 'lost'

Net

change

35 Monmouthshire 1 1 0

41 Glamorgan 22 22 0

42 Brecknockshire 8 8 0

44 Carmarthenshire 51 54 4 1 2 +3

45 Pembrokeshire 25 25 0

46 Cardiganshire 11 10 1 0

48 Merionethshire 5 5 -1

49 Caernarvonshire 6 6 0

52 Anglesey 1 1 0

Total 130 132 4 1 3 +2

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Map of survey priorities for Marsh Fritillary in Wales in 2018.

Surveillance Programme

A standardised approach to larval web monitoring (UKBMS, 2012) is used in the surveillance network. Coverage has grown from an initial ten populations in 2012 to 21 populations in 2017 (16% of Wales’ Marsh Fritillary populations). The map on Page 9 shows the location of these sites. Web surveys are undertaken by a combination of BC Wales staff and volunteers, NRW and the Wildlife Trusts, as well as Jacobs Engineering UK Ltd (on behalf of Welsh Government). Annual larval web indices (number of larval webs per hectare) are calculated to ascertain site-level trends; these are combined to produce a Wales-level species trend which is vital for reporting on conservation progress for the butterfly.

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2017 update

Larval web counts were undertaken at 19 of the 21 populations contributing data to the Wales surveillance network. Despite a dry sunny start, September was generally an unsettled month with Storm Aileen bringing strong winds and Wales getting more than its fair share of rain which brought flooding to many areas. The wet weather caused a few, but thankfully not too many, problems during the monitoring period – transects at some sites were more difficult to walk due to increased water levels and some surveys had to be rescheduled due to heavy rain. Web numbers across most of the sites in the network were generally poor although overall the Marsh Fritillary does appear to have fared better than in 2016. Seven sites showed an increase and a further seven a decrease in web indices compared to 2016 (a very poor year for butterflies in general and the Marsh Fritillary in particular). Five sites showed no change and one site was not surveyed in 2016 and therefore no comparison was possible. On monitored sites showing increases, web indices were up by between 83% and 2024%. The smallest increases were at Tir Stent in Merionethshire, where only two tiny webs were recorded compared to zero the previous year, and Blaen Cynon SAC in the Heads of the Valleys area, where an impressive 372 webs were recorded compared to 196 the previous year. Aberbargoed in Monmouthshire recovered well from 2016 with an index up by 231% (exactly 100 webs recorded), as did two of the Pembrokeshire sites (Ambleston and Puncheston Commons) with increases of 224% and 299% respectively - welcome news after web numbers crashed the previous year. In Carmarthenshire, Butterfly Conservation’s Caeau Ffos Fach Reserve and The Wildlife Trust’s Rhos Cefn Bryn reserve, had the largest web count increases with counts of 87 (689% increase) and 11 (2024% increase) respectively; not large counts themselves but much better than in 2016. On sites where web numbers were down compared to 2016, the declines were much less severe than the crashes seen the previous year. Declines of between 34% and 57% occurred at Welshmoor in Glamorgan, North Crematorium/Bryncarnau Grasslands in the Heads of the Valleys area and Yerbeston Tops (Shortland and Copybush Moors) in Pembrokeshire. On the remaining sites web numbers declined very little from the previous year. Welsh Strongholds

In 2017 the highest web density was at Puncheston Common in Pembrokeshire where 56 webs were counted at a density of 127 webs/ha. Rhos Glyn-yr-helyg in Cardiganshire maintained its recent high web counts with 334 webs counted at a density of 102 webs/ha – almost no change from the previous year (103 webs/ha). Across the network web densities were generally higher than the previous year with eight sites exceeding a density of 10 webs/ha compared to only four in 2016. However, five sites known to have supported some of Wales’s strongest populations in the last five years returned zero counts including Morfa Harlech NNR and Rhos Llawr Cwrt. The zero count at Rhos Llawr Cwrt is the first in the site’s monitoring history, although a small number of webs were found off-transect. Two other sites, Tir Stent and Welshmoor Common, which have also supported significant populations of the butterfly in the recent past returned counts of only a few webs.

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Wales-wide trend

At a Wales level, the combined data from the 21 populations continues to show an overall long-term decline between 1993 and 2017 (see graph below). The TRIM1 output (blue line on graph) shows a slight recovery from the very poor year of 2016 but web indices were still at their second lowest levels since 2009 and eighth lowest levels since monitoring began in 1993. To better separate patterns of general change from annual fluctuation, the TRIM output was run through TrendSpotter software, which produces a smooth trend through the abundance data (red line). This indicates that in the most recent five-year period (2013-17) a decreasing trend is evident in contrast to an increasing trend of the previous five-year period (2008-2012). The overall decline continues to be non-significant, however, whereas in previous years we were able to report that despite an overall decline, an increasing trend was evident from 2008 this is no longer the case. This trend is not surprising given that the UKBMS results show that 2017 was the seventh worst year for butterflies in the 42-year series which makes it five below average years in a row, not helped by variable and extreme weather.

Progress towards a representative surveillance network

Work to develop the Marsh Fritillary surveillance network continues, the aim being to make it more representative of our Welsh populations, with the majority of the key populations included. In 2017 work continued to finalise monitoring methodologies and standardise the data from two of our largest Marsh Fritillary sites: Fairwood Common on Gower (part of the Pengwern Common population) and Castlemartin Ranges on the Pembrokeshire Coast. NRW and BCW also set up web larval web transects at Rhos Talglas, an SAC/SSSI for the Marsh Fritillary in Cardiganshire. Hopefully these three populations will become part of the surveillance network in 2018.

Larval web trend for Wales 1993 - 2017 showing TRIM and TrendSpotter outputs.

1 TRIM analysis provided by the UKBMS. The multiplicative overall slope estimate in TRIM is converted into one of

six trend classification categories: Uncertain: no significant increase or decline, but not certain if trends are less than 5% per year.

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Plans for 2018

There are still a few gaps in network coverage which we will work to address in 2018 and beyond. These gaps include north Carmarthenshire, Ystradgynlais area (south Brecknockshire/north Glamorgan), north-east Pembrokeshire and the Tonyrefail area of east Glamorgan.

Concluding thoughts Butterflies in general currently appear to be at a low ebb, not helped by the variable and extreme weather which adds a further blow to butterfly populations already struggling against habitat loss, pesticides and nitrogen pollution. The Marsh Fritillary is a species that does experience boom and bust cycles as part of its population dynamics and should therefore be able to recover if good habitat is maintained. Each Marsh Fritillary metapopulation, however, needs a network of several sites close to one another to ensure its long-term survival. These sites need to support extensive suitable habitat of good quality and be well-connected to the rest of the network. Habitat condition mapping for the Marsh Fritillary strongly suggests that although the butterfly appears to be surviving in some landscapes and in some cases doing quite well, most of the networks are in fact insufficient for the long-term survival of the butterfly with some populations, including some of our larger ones, seemingly not part of a network at all. We need to improve the viability of our metapopulations through landscape-scale conservation work. Starting with the most persistent populations, we need to secure and build on the amount of suitable habitat to provide this butterfly with a future in Wales and a buffer against climatic challenges to come. Distribution surveys show that there are now 132 Marsh Fritillary populations in Wales with a small but positive net change in the past five years. This is good news and the information from surveys, surveillance and habitat mapping is allowing better targeting of our conservation work within this site network and enabling us to chart our progress towards conserving this species in Wales.

Get involved! We are always grateful for more help with surveys. If you’d like to help with the colony visit surveys in late May/June or larval web counts in September then please contact George or Clare (details on Page 8). We can provide survey guidance, maps and forms, and in many cases we can help with land access permissions too. Thank you!

Species records

If you recorded Marsh Fritillary, or any other butterfly species, last year, please send the records on to your County Recorder if you haven’t done so already. This will ensure that they are included in Butterflies for the New Millennium, the national recording scheme. A list of current county recorders can be found at: http://butterfly-conservation.org/2390/recording-contacts.html

Please also send any fritillary sightings through the 2018 season to Richard Smith

(rgsoverton@gmail.com) for inclusion in Frits About newsletters.

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Thanks!

As always, we are enormously grateful to all the individuals and organisations that carried out surveys and monitoring for the Marsh Fritillary in 2017. Without the help of volunteers our knowledge of the Marsh Fritillary in Wales would be very poor indeed. Please continue to help with surveys in the future – the information generated is incredibly valuable. Thanks also go to Ian Middlebrook for the TRIM and TrendSpotter analysis.

Contacts

George Tordoff, Senior Conservation Officer Email: gtordoff@butterfly-conservation.org Tel: 01792 642972 / 07794 521017

Clare Williams, Senior Conservation Officer Email: cwilliams@butterfly-conservation.org Tel: 07974 158814

References

Brereton, T.M., Botham, M.S., Middlebrook, I., Randle, Z., Noble D. & Roy, D.B. 2017. United Kingdom Butterfly Monitoring Scheme report for 2016. Centre for Ecology & Hydrology & Butterfly Conservation

UKBMS. (2012). Ng2: Monitoring Marsh Fritillary Larval Webs & Nf3: Marsh Fritillary Larval Web Monitoring Form. Available from ‘Resources’ area of the UKBMS website: http://www.ukbms.org/resources.aspx

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Map showing the location of the 21 populations currently contributing larval web data to the Wales trend analysis (red dots). Current (2013-2017) Welsh populations of the Marsh Fritillary shown in blue. Map also shows populations where work is currently progressing towards their inclusion in the network (orange dots) and additional gaps in the network that have been flagged up and which will be targeted in 2018 (yellow dots).