2003 BUTTERFLY REPORT

BUTTERFLY REPORT, 2003

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2003 BUTTERFLY REPORT ROB PARKER Described by Butterfly Conservation as “A vintage year for butterflies”, 2003 has indeed been an outstanding season for most species in Suffolk. The reasons are fourfold: 1. A mild winter allowed the survival of a high proportion of overwintering eggs, larvae, pupae and hibernating adults from the (below average) 2002 season.

2. The abrupt transition to a hot, dry summer meant that many species emerged en masse, causing peak numbers to exceed the norm by some 10 to 15%.

3. The continuation of the hot, dry conditions was ideal for the multi-brooded species to reproduce well, and some had an extra brood.

4. Superimposed on this, was an excellent year for migrants, with an exceptional influx of Painted Lady arriving in May and their progeny emerging in July.

The net result was an abundance of butterflies; enough for the man in the street to notice, and to catch the attention of the local media. Suffolk’s Biodiversity Action Plan (BAP) species all had strong seasons, and most of our resident species fared well too.

Weather Average temperatures were up on historic averages in every month of the season, sunshine was materially up from January to April, and rainfall was significantly low in August and September. Table 1 shows month by month temperature and sunshine for East Anglia, presented as anomalies compared to averages over the period 1961 to 1990. During the season, rainfall almost ceased on 11 August and after 15 dry days qualified for 11 continuous days of absolute drought, through to 5 September, when there was a switch to local deluges. Days of rain (>1 mm) measured close to Bury St Edmunds are shown below. The Suffolk summer passed without interruptions from gales, contributing to what was overall an unusually favourable climate for lepidoptera.

Table 1 Month May June July August September

Max Temp Anomaly Deg C 17·6 21·9 23·1 24·3 20·9

% +1·7 +2·7 +2·0 +3·2 +2·4

Sunshine hrs 197 220 204 233 224

Anomaly Rain days Rain days % +3 +13 +8 +27 +56

av 9 8 8 8 8

at BSE 12 11 11 2 4

Sources: www.metoffice.gov.uk/climate and local meteorologist Alan Messem.

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Monitoring the BAP Species The known Dingy Skipper sites were carefully monitored during May, and the effort was rewarded with the discovery of several adults flying at the Chalk Lane site, which had been feared lost. The Center Parcs colony was stronger than ever before recorded, whilst Wordwell and RAF Barnham appeared to have normal seasons. Despite searches, no Dingy Skipper were found anywhere in other apparently suitable areas. The Silver-studded Blue was first seen at Purdis Heath on 6 Jun, the earliest-ever sighting for this species, and a sign that its flight period was about 10 days ahead of normal. The subsequent counts at the Minsmere sites produced peaks that were 16% up on last year, and the results from the other sites make it clear that the Silver-studded Blue has done well everywhere in the Sandlings. The White-letter Hairstreak is not so easily counted, and it too took to the wing early, with several sightings towards the end of June. Altogether 6 new colonies were found this year, and this is encouraging in the aftermath of Dutch Elm Disease. Separate detailed accounts for each of the BAP species follow as an annex to this report.

Migrants A few Painted Lady reached Suffolk early in May via the southern counties, but the last day of May and the first two of June brought a large scale invasion across the North Sea. A sighting of 400 at Culpho, near Woodbridge was followed by reports of hundreds all down the east coast from Lowestoft to Landguard. These were observed laying eggs on our thistles whilst dispersing generally westwards, and by July we were swamped with freshly-emerged Painted Lady right across the county, often 50 to a thistle patch or 30 to a buddleja bush. Good numbers of Red Admiral and Humming-bird Hawk-moth had travelled in the same migration, and their numbers picked up in similar fashion, giving delight to plenty of observers seeing them for the first time.

2003 was not an outstanding year for Clouded Yellow, though they did become evident in July, and in some places a locally bred generation was still flying into October and even November. Two Camberwell Beauty were reported, one near Woodbridge in July, and the second at Otley, early in August. On 10 August, a single Swallowtail, presumably a visitor from Norfolk, graced Leigh Davis’ Bungay garden. This year, we have had no confirmed Queen of Spain Fritillary, just one possible sighting.

Vagrants Occasional Large Tortoiseshell have been known to turn up without explanation, and 15 April saw one at Piper’s Vale, where it remained for 2 days, allowing itself to be photographed. Whether these are escapes or passengers off the ferry is hard to know, but such delightful visitors are always of interest. Hot weather can sometimes induce unusual dispersal behaviour, and this may be the explanation for a totally unexpected sighting of a single male Chalkhill Blue at Stonham Aspal, 30 miles from the nearest colony on the Devil’s Dyke on 31 July. Intriguingly, another singleton turned up in Essex on the same day, right at the hottest point of the summer. As the Devil’s Dyke lies in the Cambridgeshire Vice-county, this is a visitor. It has strayed into our recording area before though; to Felixstowe in 1996 and otherwise not since 1923!

Trans. Suffolk Nat. Soc. 40 (2004)

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Residents Our commoner residents followed a trend of early appearance, high peak numbers and then a sharp drop-off for some species. Many recorders noticed a lull in early August, when the Ringlet, Gatekeeper and Meadow Brown all wilted, at the same time as the Vanessid numbers dropped off. The protracted drought may have had an influence here, though it was not sufficiently serious to dry out any larval host plants prematurely. It was good to have Small Tortoiseshell back in quantity, after a series of poor years, and Peacock and Comma were both reported in higher than normal counts in some places. The Brimstone delighted Ipswich residents by repaying their buckthorn planting efforts with a series of appearances in Holywells Park, where it left eggs to extend the breeding area by a few tetrads. Julian Dowding, as co-ordinator of the Buckthorn for Brimstones operation, has shown that our conservation endeavours really can make a difference. Small and Essex Skipper had another good year, but the Large Skipper was only average, as were Orange Tip and Purple Hairstreak.

Early/Late Records The good weather created earlier than ever records for 4 species: White-letter Hairstreak (20/6), White Admiral (16/6), Wall (22/4) and Grayling (21/6), whilst the fine autumn gave us 2 latest-ever records: Brimstone (16/11) and Meadow Brown (22/9). Plenty of the hibernating species were active through November, and one Peacock was still flying at North Warren on 17 December.

It remains to be seen how another mild winter will affect those species that ought to be inactive at this time of year.

Extra Broods The multiple brooded species mostly seem to have done rather well, with plenty of sightings of Small Copper, Common Blue and Brown Argus making the most of a warm September. However, an abundant autumn brood is not always beneficial if the eggs are not laid in time for the larvae to be well prepared for winter. Until next May, we shall not know. Hot conditions during the pupal stage can create aberrations, and on 31 August, Richard Stewart spotted a second brood Small Tortoiseshell of the form semi-ichnusoides. As late as 24 August, half-grown Small Tortoiseshell larvae were still being found, perhaps on their way to a partial third brood. In its coastal localities, the Wall was still flying in early October, though it remained scarce in West Suffolk. In Norfolk and Essex, the White Admiral also produced a partial second brood, which is exceptional, though not unprecedented. No second brood were reported from our own White Admiral woods, however.

Holly Blue The Holly Blue is subject to dramatic swings of abundance as it periodically falls prey to a parasitic wasp, and relatively few were seen this year, either in the spring generation, or in July. This year, records came from 75 tetrads, as against 112 in 2002 and 220 in 1996. However, one late sighting on 15 Sep could indicate a third brood for this species too.

Trans. Suffolk Nat. Soc. 40 (2004)

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Geographic Coverage The total for records received in 2003 is 8797 from 445 tetrads, about the same as in 2001, i.e. excellent, with contributions from 162 individual recorders.

However, the geographic cover is rather thin in the west of the county, and in a north-central area around Stradbroke (TM2373). The result can be seen in the map below, (created by Butterfly Conservation’s “Levana” software) and reflects a similar pattern to individual years of the Millennium survey. This achievement is a credit to all butterfly recorders, many, but by no means all, being members of SNS or Butterfly Conservation. At the conclusion of the 2004 season, the Millennium survey national distribution maps will be updated, so please keep the records coming in!

Coverage Map Suffolk 2003 KEY 1–9 species 9–16 species 20+ species

Suffolk 2003 All Records, 445 tetrads covered, with an average of 9·3 species per tetrad.

Blobs are correctly situated, but the county boundary is inaccurate in places.

Species Maps Distribution Maps for individual species have also been prepared for our 31 regulars, and these are available for reference as required. There are no maps for Swallowtail, Camberwell Beauty, Large Tortoiseshell or Chalkhill blue, though these bring the 2003 species count to an unusual high of 35.

Trans. Suffolk Nat. Soc. 40 (2004)

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Scarcity A crude assessment of relative scarcity can be deduced from a count of the number of tetrads from which each species has been recorded. Setting aside the few sightings of Camberwell Beauty, Swallowtail, Chalkhill Blue and Large Tortoiseshell, our rarest butterfly is the Dingy Skipper, which was found in only 5 tetrads (despite a dedicated search). The White Admiral was recorded from only 17 tetrads, though it is known to inhabit more. The Silverstudded Blue occupies a regular 18, and the White-letter Hairstreak 24. At the other end of the scale, 262 for the migrant Painted Lady challenged the Red Admiral’s 274, but this was just pipped by the Small Tortoiseshell at 276.

Perhaps this year, everyone was so pleased to see the Small Tortoiseshell back that they were sure to record it; impressive anyway, that it became 2003’s commonest/most widely distributed butterfly. A league table has been prepared, and follows as an annex.

Transects Detailed data was submitted for the transects at North Warren (Rob Macklin), Fynn Valley (Richard Stewart), RSPB Minsmere (Robin Harvey), Bradfield Woods (Steve Hunt), Center Parcs (Robin Bevington) Walberswick (via CEH) and Bury St Edmunds (Rob Parker). In addition, single-species transects for Silver-studded Blue were conducted at Aldringham Walks (Rob Macklin) and Martlesham Heath (Phil Smith). Special thanks are due to all those transect walkers for their regular counts over all 26 weeks of the season.

Annex: Detailed reports for BAP species.

Dingy Skipper Survey, 2003 This years searches for the Dingy Skipper were fraught by poor weather, yet some good results were achieved by determined visits to known colonies and sites where colonies have existed in the past. All visits were conducted with the landowner’s consent, or along public rights of way. A total of 10 sites were visited during the 2003 flight period, and Dingy Skipper were found at 5 of these, including the important Chalk Lane site, where it had been feared that the colony had perished. The butterfly appears to be holding its own in a very limited area of the Suffolk Brecks, though there has been progressive degradation of habitat at some sites, and the projected Thetford southern link road does present a threat to the main colony at RAF Barnham.

The Dingy Skipper was on the wing from mid April elsewhere in UK, and on the Devil’s Dyke (Cambs/Suffolk border) by the end of April, but there were no early records from Suffolk, and the survey was conducted between 5 May and 5 June – the time expected to include the main flight period. Nothing was found on 5 May at the Wordwell site, and the first sightings occurred on 15 May. Individual site reports follow: King’s Forest (Wordwell) Five volunteers checked the Wordwell colony on 15 May, and found a minimum of 6 flying along the favoured ride in bright intervals. The strip of land that has been rotovated to benefit the Basil thyme case-bearer seems to be in good condition for the future, and the Dingy Skipper were using the other side of the ride, where the Bird’s-foot trefoil was growing through moss, close to the shelter of conifers.

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King’s Forest (Chalk Lane) We were delighted to see 3 Dingy Skipper flying on 15 May, on the northern verge of Chalk Lane, in what had been a known colony in the past, but is no longer sheltered as the area to the north has been clear-felled (and re-planted).

There is a good deal of Bird’s-foot trefoil in this area, so it is to be hoped that the colony will regain its strength. A separate visit by the Suffolk Moth Group led to a further sighting of 2 Dingy Skipper in the same place on 23 May. King’s Forest (John O’Groats Cottages) Occasional past reports from this area made a search worthwhile, and this was conducted in good weather on 15 May. Some Bird’s-foot trefoil was growing along a wide ride, but no Dingy Skipper were found. The Mother Shipton moth (a similar looking insect) was present, however.

Elveden (Center Parcs) A bright interval on the morning of 19 May provided an encouraging result from this site, where only one individual had been spotted during the 2002 season. A total of 5 Dingy Skipper were observed, one on the “David Bellamy meadow”, and the rest on the adjacent rough ground. Two were in courting flight. Although the grass is rank in places, parts of the rough ground held strong patches of Bird’s-foot trefoil, close to the shelter and bare ground provided by a drainage channel. Access has been improved by the creation of a mown path in a loop through this area, and the shorter turf and bare soil here seemed to attract the butterflies.

RAF Barnham This important site was visited by a party of six on 20 May, regrettably in unfavourable weather conditions. There have been some alterations to the habitat as a result of the dismantling of the fences surrounding the plantation areas, and, more importantly, due to the rapid growth of the trees, which are shading out some of the areas in which the foodplant grows. The visit was worthwhile, even though nothing was seen simply because the weather was not adequate for the butterfly to fly. Fortunately, 2 Dingy Skipper seen just outside the boundary fence on 24 May confirmed that the colony survives. A further visit on 5 Jun, rather late in the flight period, found 3 well worn adults still flying between rainstorms. The projected route for the Thetford southern link road lies across the northern edge of the present colony, and threatens its future.

Barnhamcross Common This site lies adjacent to RAF Barnham, and occasional strays are seen on the south edge of Barnhamcross Common, which lies in administrative Norfolk, but in Suffolk’s biological recording area. In marginal weather on 24 May, 2 were found within 20 m of the boundary fence, just 100 m from the main colony on RAF Barnham. This sighting confirms that the main colony survives, rather than proving that they are now breeding on Barnhamcross Common itself. Indeed, a search further north and west did not discover any more Dingy Skipper, though there was some Bird’s-foot trefoil.

Trans. Suffolk Nat. Soc. 40 (2004)

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Marmansgrave Wood There have been very few Dingy Skipper sightings from this area in recent years. An inspection on 24 May found only a very small amount of Bird’s-foot trefoil in rather overgrown habitat, and no Dingy Skipper were seen. A later inspection by BC’s Regional Officer for the East of England concluded that the habitat had deteriorated to the point that considerable resources would be required to turn it around.

Euston Quarry This wonderful CWS (on private land) has everything that ought to make a good Dingy Skipper site, including Bird’s-foot trefoil and a Common Blue colony. It was inspected twice, in marginal weather on 19 May, and again in good weather on 26 May, but no Dingy Skipper were found.

North Farm/West Farm Just south of RAF Barnham, a disused railway line presents a possibly suitable site, and this was inspected on 24 May. It runs from North Farm (Euston Estate) past the East of England Tank Museum (aka the tyre dump) to West Farm (Elveden Estate/Stamper Farms), and features Bird’s-foot trefoil in rather rank grass, with some promising disturbed ground in the area used for tank driving. No Dingy Skipper were seen, and the terrain is judged marginal, but worth an occasional re-inspection in future years.

Barnham Heath SSSI This site is close to RAF Barnham, but had never before been checked sufficiently early in the season. A quick look in marginal weather on 19 May gave no reason for optimism, as very little Bird’s-foot trefoil was evident; it looked more suitable for Grizzled than Dingy Skipper.

Silver-studded Blue Counts 2003 The season got off to an early start, with a record early sighting at Purdis Heath on 6 June, suggesting that the flight period would be about ten days in advance of a “normal” year. Where possible, the counts were brought forward to avoid missing the peak population. At Minsmere, a combined BC/RSPB team of nine counted 1378 SSBs in one day (4 July) at the six strongest colonies, 200 up on last year, and the other counts were equally healthy. The Sandlings Group assembled the count data for the sites under their combined management, and the overall picture is quite encouraging, with progressive improvement to the habitat maintenance programme being initiated. The main effort goes into checking encroachment by gorse and bracken, and in creating areas of low-growing “pioneer” growth of Bell-heather. A very successful joint work party was organised at Purdis Heath, where encroachment by silver birch also needs to be reversed.

The Wenhaston Blackheath colony deserves special mention, since it appeared in 2002 to be on the brink of extinction. Happily, a handful of Silverstudded Blue survived, and egg-laying was observed this year. Hopefully the habitat restoration work undertaken at the margins of the flight area will benefit both the black ants and the butterflies in future years.

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The Martlesham Heath colonies were counted as usual on the second Sunday in July, but 13 Jul 2003 was too late for the peak flight period in this very early season, and the low count (316, about 50% of normal) does not reflect a population crash. Indeed, the single-species transect there suggests that 2003 was a good year, bucking the trend of progressive decline resulting from the heather growing too “leggy”.

Martlesham aside, the other sites recorded totals 10 to 20% up on the 2002 figures. There were also records from 3 previously unrecorded sites. The hot weather may have encouraged dispersal away from established breeding centres, and it remains to be seen whether fresh colonies have become established.

Despite the good counts, there are grounds for serious concern about the decline in habitat area and quality. Working under contract to the Suffolk Wildlife Trust, Neil Ravenscroft undertook a detailed survey of selected Sandlings sites, and this drew attention to the long term decline at Purdis Heath and Martlesham Heath. Two recent work parties have cut back the encroachment by scrub and Silver Birch at Purdis, and plans are being laid for suitable restorative management at Martlesham.

White-letter Hairstreak Survey Our population of White-letter Hairstreak seems to be surviving despite the ravages of Dutch Elm Disease. Although we have lost many of our mature elms, there remains an abundance of elm in the hedgerows of Suffolk, and searches are progressively detecting small colonies living on the “sucker” elm.

It nonetheless remains scarce, and under-recorded, and has been accepted as a Suffolk BAP species. Survey work this year confirmed a couple of tentative sightings from 2002, and most encouragingly, Sharon Hearle proved that determined searching could unearth previously undetected colonies; she found no less than 5 on trees and windbreaks around Newmarket. Two further sightings occurred this year at fresh sites not far from known colonies. Checks at other established sites confirmed continuing presence; nowhere was a possible extinction identified with this difficult to monitor species.

The Millennium survey noted a significant decline since the 1986 survey, but recorded White-letter Hairstreak in a total of 42 tetrads during the 5 year survey. In 2002 and 2003, they were found in 16 tetrads (11 common to both years, so 21 together).

Rob Parker 66 Cornfield Road Bury St Edmunds Suffolk IP33 3BN

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Annex: A Measure of Scarcity tetrads per species (2003) Tetrads Species

Remarks

1 1 1 2 5 17 18 24 29 37 40 51 75 79 81 84 86 90 93 107 136 137 144 150 183 194 210 210 222 233 234 240 262 274 276

First Suffolk record in 8 years Possible release Norfolk stray

Chalkhill Blue Large Tortoiseshell Swallowtail Camberwell Beauty Dingy Skipper White Admiral Silver-studded Blue White-letter Hairstreak Green Hairstreak Clouded Yellow Purple Hairstreak Grayling Holly Blue Wall Brown Argus Essex Skipper Large Skipper Small Heath Brimstone Small Skipper Small Copper Ringlet Orange-tip Common Blue Gatekeeper Green-veined White Comma Peacock Meadow Brown Speckled Wood Small White Large White Painted Lady Red Admiral Small Tortoiseshell 35 species seen in Suffolk

BAP species; scarcest resident UKBAP species BAP species Migrant

Poor year

New records in East Suffolk

Exceptional migration year Recovered to “commonest” after 3 poor years

Trans. Suffolk Nat. Soc. 40 (2004)