BUTTERFLY REPORT 2011
127
2011 BUTTERFLY REPORT ROB PARKER 2011 was a very confused season, with extremes of weather causing unseasonal flowering of many plants and inevitable knock-on effects for insect life. New earliest-ever emergence times were registered for eight butterfly species, whilst autumn brought latest-ever sightings for five different species. On the other hand, there were long blank weeks midseason, with practically nothing flying. Not only did Purple Emperor, Silverwashed Fritillary and Marbled White all remain in evidence, but unexpected appearances by three other species made an unusually high count of 38 species, although several of these were possibly released specimens. It was another year of poor outcomes for our commoner butterflies, but good news for several UKBAP species. Good recording effort has resulted in decent coverage for the second year of the current five-year period. Annexes A and B provide analysis of the season’s results and compare them with previous years. Weather A second cold winter started with snow before Christmas 2010, and 35 frosty days reduced the survival rates of butterflies and parasites alike. Spring was not particularly early, but it was warm and dry. Judged by historic averages (see Table 1 below) it was 2 degrees warmer, with only 27∙8% of an average spring’s rainfall. Larvae feeding up did well, and flew early. Drought was a frequently heard word in spring and autumn, and East Anglia was much drier than the rest of UK. Although late June and early July were fine, and suited Silver-washed Fritillary and White-letter Hairstreak, the rest of summer was below par. An extended autumn was warm and sunny, yet many species produced disappointing second broods.
Table 1. 2011 Weather for East Anglia Season Winter 10/11 Spring Summer Autumn
Mean Temp
Anomaly
Sunshine
Anomaly
Rainfall
Anomaly
ºC
ºC
hrs
%
mm
%
3∙5 10∙6 15∙7 12∙9
-0∙8 2∙1 -0∙2 2∙4
121 563 528 402
69 125 90 124
132∙1 27∙8 179 81∙3
90 21 119 47
Source: www.metoffice.gov.uk/climate/uk/2011 Anomalies are measured against the 1971 to 2000 averages [as last year].
Trans. Suffolk Nat. Soc. 48 (2012)
128
Suffolk Natural History, Vol. 48
Residents – Winners and Losers Once again, many garden recorders remarked on the poor showing of their regular species. Yet a high proportion of early sightings were Small Tortoiseshells, with rather less Peacocks and good numbers of Brimstones emerging from hibernation on fine days from late February onwards. Counts of most species over the whole season from transect walks showed poor attendance, with notably weak numbers for: Essex and Small Skippers, Common Blue, Small Tortoiseshell and Peacock. Many of our common species were found in less than 80% of the tetrad count achieved in 2010 – itself a mediocre year. See Appendix A for a direct comparison. Early and Late The spring heatwave seemed to suit developing species, and earliest-ever records were noted as follows: Over wintering stage Pupa: Green Hairstreak. Larva: Common Blue, White Admiral, Silver-washed Fritillary, Ringlet. Ovum: Purple Hairstreak, White-letter Hairstreak, Silver-studded Blue. This suggests that larval feeding and development was considerably accelerated by the warm, sunny conditions before the drought had dessicated the larval host plants. All of the single brooded species above had a successful season, but the double brooded Common Blue, despite its early emergence, had a thoroughly poor year. Conditions in late summer/early autumn were also warmer, sunnier and drier than average, and this resulted in the following latest-ever records; Voltinism (“Broods”) Single-brooded: Silver-washed Fritillary. Double-brooded: Holly Blue, Small Heath. Multiple-brooded: Large White, Speckled Wood, (Small Copper equalled latest). It is most unusual to log so many early/late records (eight early and six late) in one season, although early and late claims for Silver-washed Fritillary are not significant since it is such a new species to the county. Monitoring the BAP Species There are seven Suffolk BAP species, including two in the “for study only” category. Silver-studded Blue The early emergence of the first few caused us to bring forward the annual survey, and with hindsight, we brought it a bit too far forward and missed the peak at Minsmere by a few days. As a result, the number counted – over 4000 at 33 sites – was less than last year (See Annex C for full results). In the Dunwich Forest, where the Westleton Heath population has re-colonised a
Trans. Suffolk Nat. Soc. 48 (2012)
BUTTERFLY REPORT 2011
129
former forest compartment, it was pleasing to note an expansion in numbers. The colony translocated to Blaxhall common in 2007 again had its best-ever year, with its longest-ever flight period (eleven weeks) and a highest singleday count of 45 butterflies. The colony on Walberswick NNR is a fresh cause for concern, as none were found there this year, following an abrupt decline over the past three seasons. Habitat improvement work at Purdis Heath reflects a more active approach to conserving the isolated colonies on the Ipswich heaths. Dingy Skipper The Dingy Skipper was not found at RAF Barnham for the sixth year in succession, and the colonies there and at Center Parcs have evidently been lost. Happily though, it turns out that there is still a colony in the pits on the adjacent Thetford Heath nature reserve, which had not been searched previously due to the presence of nesting stone curlew. This is very close to the recently-planted compartment of the Thetford Forest where a few were seen last year. In the King’s Forest, decent numbers are still breeding around the archery site. None were found at the southern end of the forest, but the prospects are promising, as felling has opened the rides to more sunlight. See Annex D for more detail. White-letter Hairstreak This species had a good year. The long spell of hot sunny days in June encouraged White-letter Hairstreaks down from the elm canopy to find nectar at bramble and thistle. See Annex E for more detail. White Admiral White Admiral also had another good season, though not as good as 2010. The colony in Bradfield Woods has now been present for seven consecutive seasons. See Annex F for more detail. Grayling This species is in general decline across Suffolk, although this years West Suffolk results were rather better than 2010; five recorders saw Graylings in eleven different tetrads. Fortunately, it continues to fare well at its haunts in the Sandlings, including Dunwich Forest, where it is now monitored on two transects. See Annex G for more detail. The UK BAP list includes two study species for enhanced monitoring. In both cases, Wall and Small Heath, the larval host plant is grass: Wall Wall is in decline in the UK and in Suffolk, and for that reason, a single species survey was undertaken in 2011. The results were disappointing; for the second year in succession, none were found in West Suffolk, and many of the target tetrads did not yield any records in places they had been present four or five years previously. Results from the 2011 survey are to be found at Annex H.
Trans. Suffolk Nat. Soc. 48 (2012)
130
Suffolk Natural History, Vol. 48
Small Heath This species is in a less critical situation than the Wall, but is losing ground on farmland amongst fertilized grass. It was recorded from 234 tetrads in the last complete five-year survey (24% of 994 recorded tetrads), but numerical counts are falling at the few transect sites which still support it, but has made a slight recovery over the past three years. Purple Emperor The introduced Purple Emperors were still flying in Theberton Woods, and on one occasion, a mating pair was photographed in the canopy. This year, singles were also seen at Minsmere and further afield at North Warren. Migrants 2011 was another poor year for migrants, with just eleven Clouded Yellow all year, and Painted Lady recorded from only 84 tetrads (12% of the recorded squares); most of them along the coast in September. Large White numbers were generally low, and it may be that there was no significant immigration for it either. The Red Admiral, a migrant species now successfully over wintering here, was widely recorded, largely due to breeding here, and partly thanks to the September immigration. Silver-washed Fritillary The spread of Silver-washed Fritillary continued during 2011, and it appears to be breeding in at least two of the twelve woods from which it has now been recorded. This year, no less than 34 different recorders saw this new arrival, and hopefully it is now going to stay in Suffolk. This has to be the best possible news. Encouragingly, Essex, Cambs and Norfolk have all experienced an upswing in Silver-washed Fritillary sightings too. Unusual Sightings 2011 was an odd year in many ways, and the number of non-resident species appearing was higher than ever. A single Monarch on the Shotley peninsula is assumed to have been an escape from the butterfly house at Jimmy’s Farm. Two separate Swallowtails remain unexplained, as does a single Queen of Spain Fritillary in Dunwich Forest. There were also two separate Dark Green Fritillary sightings, one at Pakefield Cliffs (south of its Norfolk habitat) and the other at Barnhamcross Common, (further from its closest Norfolk localities). An autumn Long-tailed Blue turned up close to the coast at Lowestoft, which like the September 2010 example could have been a stowaway in fresh vegetable produce. Finally, the Marbled Whites seen in Ipswich’s Landseer Park were present in larger numbers this year, so these appear to have bred there, whatever their origins. Discounting the Monarch, that still leaves five unusual visiting species, any of which could have been natural arrivals. Added to our regular species, this would bring the total species count for the year to 38. Is that a biodiversity record, or a freak year? These last five species have been listed in the “Scarcity” table (Annex A) but excluded from the long term analysis (Annex B).
Trans. Suffolk Nat. Soc. 48 (2012)
BUTTERFLY REPORT 2011
131
Recording and Geographic Coverage Despite the poor showing by butterflies, this was a good year for records. A total of 678 tetrads were visited, bringing the season’s cover to 62%. After two years of the current five year period 807 tetrads (74%) have been visited. For the first time, the results of BC’s “Big Butterfly Count” were incorporated. This was an exercise in popular science, with many novice recorders searching for 15 minutes in one location, so the contribution was mainly common species, often from tetrads that were already well-recorded. Having said that, it has involved fresh enthusiasm, and we have recruited a number of new recorders. The area covered most thinly remains the agricultural land in High Suffolk, where both the human population and the butterfly density are inherently low. The Wall survey is updating our knowledge of its decline, but sadly not adding much to our records. Targets for next year include extending the SNS Wall survey and visiting the remaining 26% of the county. Species Maps Distribution Maps for individual species have been prepared for our 31 regular species, and these are available for reference as required. The average number of species recorded per tetrad was just 8∙7, reflecting the shortage of migrants and the poor showing of a handful of common species. Analysis The species that put in an appearance this year are shown in Annex A, in order of scarcity, with a direct comparison to last year’s turnout. Our most widespread residents were again reshuffled, with Red Admiral taking over from Small White as our most widely distributed butterfly, and Meadow Brown falling back to 6th place. Small Tortoiseshell, the 2005 leader, now sits back in 11th place, behind Peacock and Comma. Each species’ distribution relative to last year is expressed in the “c.f. last” column. Although White Admiral had a good year, it shows poorly by this measure simply because it had an outstanding 2010. Trends over a longer period are presented separately at Annex B for our 31 regulars. The latest five year rolling data again covered over 1000 tetrads, and reflects the same long term distribution trends noted last year. However, the declining abundance of common butterflies has not yet fed through to reducing distribution. Once again, to those thinking about long-term declines, the table at Annex B merits close study. Transects Analysis of transect results gives a sharper view of trends than distribution maps. The 19 full transects walked this year indicate the progressive decline of several species including Small/Essex Skippers, Common Blue, Small Tortoiseshell, Small Heath and Grayling (where monitored). These species are also noted to be in long-term decline nationally, according to the UK BMS results. Peacock also had a poor showing in what was an average year overall for most of the Suffolk transects. New transects began at Nowton Park and
Trans. Suffolk Nat. Soc. 48 (2012)
132
Suffolk Natural History, Vol. 48
Black Heath, and thanks are due to the following, who put in dedicated monitoring effort at: North Warren (Dave Thurlow), Minsmere (Robin Harvey), Bradfield Woods (Steve Hunt), Center Parcs (Graham Hersey-Green), Cavenham Heath (Michael Taylor), Walberswick (Will Russell), Spring Lane (Rob Parker), Ramsey/Hintlesham and Wolves Wood (Mark Nowers), Newsons Farm (Frances Bee), Upper Abbey Farm (Trudy Seagon), Alton Water (Simon Waters), Manor Farm (Brenda Hudson) , Tythe Farm (Peter Vincent), Dunwich Forest 1&2 (Dayne West), Arger Fen (Kerry Vaughan), Black Heath (Linda Hammond) and Nowton Park (Fay Jones). Single-species transects for Purple Hairstreak (Steve Hunt) and Silver-studded Blue (Terry Peake) also produced useful results. In almost every case, additional volunteers (not named individually) assisted the lead walker. At present the Combs Wood transect is vacant and awaiting a volunteer walker.
Notes to Annex A: 1 Swallowtails, Queen of Spain Fritillary and Long-tailed Blue may not have arrived naturally. *cf last Indicates the prorortion of last year's cover achieved in the current year. 38 species seen in Suffolk 2011 (including introduced Purple Emperor, Marbled White and all possibly natural vagrants)
Trans. Suffolk Nat. Soc. 48 (2012)
BUTTERFLY REPORT 2011
133
Annex A. Scarcity for 38 species seen in Suffolk in 2011. Tetrads per Species – 2010 & 2011 (Species listed in order of scarcity in 2011) % of 575
Tetrads 2010
0∙ 3 0∙ 2
2 1
0∙ 2
1
0∙ 7 0∙ 2 0∙ 7 1∙ 4 2∙ 6 1∙ 6 4∙ 5 4∙ 3 8∙ 9 7∙ 3 8∙ 9 11∙5 15∙3 21∙7 17∙4 19∙3 28∙0 33∙0 30∙6 38∙6 33∙9 40∙2 43∙5 49∙0 53∙0 52∙0 46∙3 56∙7 61∙4 48∙9 50∙8 59∙8 66∙8 55∙7
4 1 4 8 15 9 26 25 51 42 51 66 88 125 100 111 161 190 176 222 195 231 250 282 305 299 266 326 353 281 292 344 384 320
Species
Camberwell Beauty Long-tailed Blue Queen of Spain Frit. Marbled White Dark Green Frit. Swallowtail Purple Emperor Dingy Skipper Clouded Yellow Silver-studded Blue Silver-washed Frit White-letter Hairstreak Wall White Admiral Grayling Green Hairstreak Purple Hairstreak Essex Skipper Painted Lady Small Heath Brown Argus Small Skipper Small Copper Large Skipper Common Blue Brimstone Holly Blue Ringlet Small Tortoiseshell Peacock Comma Orange-tip Gatekeeper Meadow Brown Speckled Wood Green-veined White Large White Small White Red Admiral
Tetrads % of 678 *cf last 2011 tetrads
1 1 1 2 2 3 4 11 15 16 26 31 32 48 62 72 79 84 118 121 148 169 188 194 197 220 226 276 285 308 311 323 360 363 366 380 419 452
0∙ 1 0∙ 1 0∙ 1 0∙ 3 0∙ 3 0∙ 4 0∙ 6 1∙ 6 2∙ 2 2∙ 4 3∙ 8 4∙ 6 4∙ 7 7∙ 1 9∙ 1 10∙6 11∙7 12∙4 17∙4 17∙8 21∙8 24∙9 27∙7 28∙6 29∙1 32∙4 33∙3 40∙7 42∙0 45∙4 45∙9 47∙6 53∙1 53∙5 54∙0 56∙0 61∙8 66∙7
0∙85 0∙42 2∙54 0∙85 1∙17 0∙85 1∙51 0∙85 1∙05 0∙53 0∙97 1∙03 0∙93 0∙76 0∙57 1∙00 0∙92 0∙78 0∙75 0∙91 0∙74 0∙86 0∙81 0∙77 0∙83 0∙79 0∙87 0∙99 0∙84 0∙86 1∙10 1∙06 0∙94 0∙93 1∙20
Remarks
None prob stowaway Note 1 11 sightings Note 1 Note 1 2 dispersals noted 1 on Nflk border few migrants dispersal cont. Survey: nil in TL
a good year a good year a poor year few migrants
poor year poor year poor year weak 2nd gen.
good autumn
Trans. Suffolk Nat. Soc. 48 (2012)
134
Suffolk Natural History, Vol. 48
Annex B. ANALYSIS – 2003 to 2011 Long term trends - for residents and regular visitors. Survey from: to:
2003 2007
2004 2008
2005 2009
2006 2010
2007 2011
Period: Tetrads:Species/Tetrad:
5yrs 879 12.6
5yrs 918 12.7
5yrs 994 13.1
5yrs 1003 13.4
5yrs 1003 13.6
Small Skipper Essex Skipper Large Skipper Dingy Skipper Clouded Yellow Brimstone Large White Small White Green-veined White Orange Tip Green Hairstreak Purple Hairstreak White-letter Hairstreak Small Copper Silver-studded Blue Brown Argus Common Blue Holly Blue White Admiral Red Admiral Painted Lady Small Tortoiseshell Peacock Comma Speckled Wood Wall Grayling Gatekeeper Meadow Brown Ringlet Small Heath
349 281 325 8 119 368 637 657 594 480 103 123 75 371 21 230 402 454 65 640 472 655 585 526 608 160 100 558 648 438 229
362 296 347 8 104 394 683 685 632 522 108 116 81 369 21 215 404 502 68 655 403 644 621 557 636 136 95 593 699 473 236
390 296 412 8 118 442 785 775 718 552 113 128 79 376 22 260 475 504 71 699 604 698 700 635 724 120 104 663 789 528 234
411 292 439 8 118 461 806 799 731 565 119 147 83 402 21 292 505 498 79 720 615 701 714 663 720 115 108 701 805 571 241
405 278 462 7 85 463 820 813 765 618 134 159 79 397 21 297 499 520 78 751 557 689 721 672 738 100 104 725 804 587 252
Trans. Suffolk Nat. Soc. 48 (2012)
BUTTERFLY REPORT 2011
135
Annex B. ANALYSIS – continued Survey from: to:
2007
2008
2009
2010
2011
Period: Tetrads:Species/Tetrad:
1yr 509 9.1
1yr 549 9
1yr 645 10.3
1yr 575 9.7
1yr 677 8.7
Small Skipper Essex Skipper Large Skipper Dingy Skipper Clouded Yellow Brimstone Large White Small White Green-veined White Orange Tip Green Hairstreak Purple Hairstreak White-letter Hairstreak Small Copper Silver-studded Blue Brown Argus Common Blue Holly Blue White Admiral Red Admiral Painted Lady Small Tortoiseshell Peacock Comma Speckled Wood Wall Grayling Gatekeeper Meadow Brown Ringlet Small Heath
110 83 124 2 29 174 276 303 248 205 49 30 23 159 15 90 128 190 23 338 180 197 288 243 291 27 32 236 294 171 87
125 99 131 2 5 157 343 305 307 236 35 33 24 145 15 38 128 197 32 289 68 241 307 300 317 28 37 281 361 246 84
169 106 199 5 57 199 469 425 392 244 41 56 16 188 17 128 249 153 26 283 447 398 408 351 411 36 54 354 434 268 100
161 88 176 4 8 195 344 384 292 266 51 66 26 190 15 111 222 231 51 320 125 282 305 299 281 27 42 326 353 250 100
148 79 188 4 11 197 380 421 366 311 62 72 26 169 15 121 194 220 32 452 84 276 285 308 363 31 48 323 360 226 118
Trend
Weak Migrant: variable Expanding Strong recently
Gaining Gaining Stable Gaining
Doing Well Doing Well Migrant: variable Decline Checked
Still doing well Serious Decline Weak but Stable
Slight recovery
Trans. Suffolk Nat. Soc. 48 (2012)
136
Suffolk Natural History, Vol. 48
Annex C. Annual Report on Silver-studded Blue for 2011 Season The exceptionally long hot sunny spring of 2011 brought a record first sighting from Rob Macklin on 30 May at Aldringham Walks. This was an earliest-ever emergence, beating the previous record (4June 2007) by five days. This led to a swift decision to bring the Minsmere count forward to 13 June, which, in the event, proved to be about four days ahead of the peak. Thereafter, the flight period passed briskly, thinned in July and was effectively over by the middle of August. Positive Developments The new colony in the heathland re-generation compartment at the SW corner of Dunwich Forest (TM461702) is doing nicely; 64 SSB were counted there this year. The emergency habitat restoration programme at Purdis Heath achieved its first year objectives and some of the 10 SSB seen were flying over the recently foraged areas. Blaxhall Common The transect walk at Blaxhall Common achieved a record index of 155, finding up to 45 Silver-studded Blues on the wing over a nine week period from 2 June to 28 July. This marks four seasons of progressively rising numbers flying for a longer flight period each year, which is most encouraging. A field meeting on 9 July included a search of the grazed heath to the south of the road, but it would appear that the colony remains north of the road. Results of Annual Count All the main sites were counted, mostly just off the population peak, and in windy conditions. Some of the lesser sites again went uncounted. A total of 33 out of 47 sites were counted, and the resulting total figure of 44524 was unexceptional. At 83% of the 2006 datum, that reflects a reasonable count for an average year. Most colonies are in good health, but three remain where there is longstanding cause for concern. Alarmingly, at Walberswick NNR not a single SSB was found, which suggests the loss of an important colony. The heather encroachment at Minsmere Potbriggs will be tackled this winter. Weak Colonies The colonies about which concern has been expressed since 2005 are Purdis Heath, Blackheath, which are struggling along at low population levels, and Martlesham Heath a larger site which still has reasonable numbers despite concerns over deteriorating habitat. The habitat improvement at Purdis Heath could result in discernible benefits in the next few years. Martlesham Heath has suffered more fires this year, causing short-term damage to the population which should be reversed as fresh pioneer growth develops. The cause of the population crash at Walberswick is uncertain, but could be the result of flooding by slurry from an adjacent pig farm, which is soon to be relocated.
Trans. Suffolk Nat. Soc. 48 (2012)
BUTTERFLY REPORT 2011
137
Ant Studies Prior to the annual count, field studies in two of the Minsmere colonies found SSB larvae and pupae on the soil above ants nests. It was established that the ants hosting the Reversion Field colony are Lasius niger, whilst the nearby colony in the sandy soil of the Sandpit site is hosted by Lasius psammophilus. Further studies into ant-butterfly mutualism could be helpful in conserving our threatened colonies. Tabulation The results of the 2011 counts are tabulated in the accompanying spreadsheet. Of the 33 sites surveyed, two were unoccupied, including Walberswick NNR where the colony may have been lost. The total count represents 83% of the 2006 datum, making 2010 an average year. Past tabulations have shown Upper Hollesley Common 3d and Dunwich Heath; both sites have occasionally recorded strays, but since neither of them are established colonies, they will be delisted from 2012 onwards. 2011 COUNTS –Monitored Silver-studded Blue Sites listed geographically from the North Location Blackheath Wenhaston Walberswick Comn Walberswick NNR Dunwich Forest Area 4 Westleton Heath NNR Westleton Common Westleton Football Pch. Minsmere Foraged Sq. Minsmere Reversion Fd. Minsmere Sawmills Minsmere Football fld. Minsmere Natterjack pit Minsmere SW Comp 1 Minsmere Pit Comp2 Minsmere SE Comp 3 Minsmere Comp 20 N Minsmere Comp 20 S Minsmere S Comp3 Minsmere Central C.3 Minsmere Powerlines Minsmere N. Bridleway Minsmere Potbriggs Minsmere N. Grimstones
Grid Ref. TM420749 TM491752 TM451727 TM461702 TM4569 TM443687 TM444688 TM459689 TM451689 TM452692 TM451691 TM451693 TM450694 TM457692 TM457691 TM446683 TM445680 TM456693 TM453693 TM461683 TM468687 TM468689 TM462688
Date
Observer
♂
♀
Total
17/8
R. Havard
4
1
5
24/6 14/6 24/6 26/6 26/6
W. Russell M. Kemp W. Russell D. Rous D. Rous
0 59 26 113 22
0 5 13 24 4
0 64 39 137 26
13/6 13/6 13/6 14/6 14/6 14/6 14/6 14/6
M. Kemp M. Kemp M. Kemp M. Kemp M. Kemp M. Kemp M. Kemp M. Kemp
163 276 172 69 10 492 544 351
40 69 3 19 0 167 161 71
203 345 175 88 10 659 705 422
14/6 14/6
M. Kemp M. Kemp
13/6
M. Kemp
~ ~
503
92
595
Continued over page
Trans. Suffolk Nat. Soc. 48 (2012)
Suffolk Natural History, Vol. 48
138 Location Minsmere E Comp 13 Minsmere C.13 track Minsmere C.13 Tanktrap Dunwich Heath Minsmere Gravel Pit Aldringham Walks Blaxhall Common Upper Hollesley MOD SCDC Lower Hollesley 'A' Lower Hollesley 'B' Lower Hollesley 'C' LHC Barthorpes small LHC compt 1e Firebreak LHC compt 8c Rushmere Heath Martlesham Heath Parsnip Plantation Ipswich Golf Club Purdis Heath Ransomes CWS Ind. Est. Jacobsen Ind. Est. lagoon fringe
Grid Ref. TM468681 TM464681 TM466683 TM468687 TM449669 TM464612 TM377566 TM337480 TM333472 TM335471 TM342465 TM343461 TM350458 TM349460 TM346462 TM350456 TM338468 TM202448 TM2344 TM327458 TM208432 TM212427 TM207419 TM200410 TM207415
Date
Observer
♂
♀
Total
14/6 14/6 14/6
M. Kemp D. Thurlow P. Locke
10 41 40
1 5 5
11 46 45
26/6
N. Mason
19
1
20
27/6 27/6 20/6 20/6 20/6 20/6
R. Stewart R. Stewart N. Mason N. Mason N. Mason N. Mason
53 248 61 5 4 1
5 38 7
58 286 68 5 4 1
26/6 30/6 5/6 23/6 21/6
P. Smith A. Morgan N. Sherman J. Dowding J. Dowding
not split 4 1 6 4 38 18
454 4 1 10 56
21/6
J. Dowding
0
Sites counted: 33 of 47 With two empty
2011 Totals: 3334
754
4542
Datum good year:
2006 Totals: 3617 1438
5470
This year as
% of 2006:
83%
Trans. Suffolk Nat. Soc. 48 (2012)
BUTTERFLY REPORT 2011
139
Annex D. Dingy Skipper Survey, 2011 Overview Whilst the Dingy Skipper appears to have been lost from the formerly strong site at RAF Barnham, an important discovery was made this year in the adjacent Thetford Heath nature reserve, where a colony survives in some old pits. The smaller colony at Center Parcs Elveden has apparently been lost. This year’s survey shows that the colony in King’s Forest is still breeding in the area around the Archery ranges, and flying more widely in the forest. Felling and clearing operations around the Wordwell ride have opened two areas potentially suitable for recolonization by the Dingy Skipper. 2011 Survey This year’s survey involved 16 recorders, and 26 man-days, but searches at Center Parcs and RAF Barnham again failed to find any Dingy Skippers. The first sighting on the county border close to Thetford Heath was on 4 May, followed in the King’s Forest on 6 May. The highest count of 21 was achieved in good weather on the pre-planned count of 13 May. The season advanced rapidly in the hot weather and by 20 May they were scarce in King’s Forest, although one was reported on the Norfolk border still flying on 4 June. The sites visited are listed below, with more detail. This year’s effort was again focussed on defining the breeding area within the King’s Forest, with a view to extending the suitable habitat. RAF Barnham TL8580/8680 A thorough search was made in suitable weather on 9 May, but not a single Dingy Skipper was seen. Some bird’s-foot trefoil was present, and although some of the habitat looked suitable, most of the former flight area is shaded out. It seems that the Dingy Skipper is no longer breeding on the SSSI. Last seen here in 2005. Thetford Rifle Range (MoD) TL8481 A quick afternoon visit here on 20 May confirmed the apparent suitability of the sward on the secondary firing range. To date, no Dingy Skippers have ever been seen here. Thetford Forest/Thetford Heath TL8480 Last year’s unexpected sighting just outside RAF Barnham led to a more thorough search of this area. Sharon Hearle found four flying in 2010 in a replanted compartment of the Thetford Forest, (TL848808). This plantation lies just 200 m NW of RAF Barnham’s boundary fence, and about 400 m from Marmansgrave Wood, where a colony flew until it became overgrown in the late 1990s. Close by is Barnham Heath, a nature reserve managed for stone curlew by the Norfolk Wildlife Trust - even though it lies in Suffolk. Special arrangements were made to look for Dingy Skipper here and these proved successful, with a small colony being found by the warden Darrell Stevens in the pits at the north of the reserve. This colony would have been the source of the Dingy Skippers again found in the plantation on 4 May.
Trans. Suffolk Nat. Soc. 48 (2012)
140
Suffolk Natural History, Vol. 48
Center Parcs, Elveden TL810805 This isolated colony existed on a small site that has been losing its suitable habitat to a build up of coarse grass. The cutting and rotovation work has not really created significant patches of bird’s-foot trefoil. Center Parcs staff visited the area regularly in May, without seeing any Dingy Skippers. Last seen here in 2006. In King’s Forest (overall): First found 6 May (earlier than usual). Best count: 21 on 13 May. Latest sighting: 14 May. Extent: From Wordwell to Chalk Lane, but confined to two tetrads, despite strays to the east of the Archery area. King’s - Chalk Lane area (TL8275 and 8374) Just three were seen on Chalk Lane and the parallel path just north of it, all on the organized search on 14 May. King’s - Archery Restricted area TL833737 The secluded open area between the mature beech to north and plantation to south seems to be the main breeding site (TL834739). The flight area extends along the east-west ride (204) south of the Archery hut to TL838734. The north-south conservation ride (205) bounding the archery restricted block was again in use as a regular flight area. The highest one-day count in this area was 20 on 13 May. Just to the north (TM838739) one extra Dingy Skipper was found on a patch of bird’s-foot trefoil in a heathland square where they have not been found before. King’s – Griffin’s Covert (East of Archery area) Although no sightings were made at the edge of Griffin’s Covert this year, the habitat remains suitable. King’s - Wordwell area TL834733 Conservation felling has widened the main ride by 30 m, and this allows more sunlight into the strip where the bird’s-foot trefoil grows. The stumps have now been lifted, and some bird’s-foot trefoil seed has been spread in the east-west ride close to the southern edge of the forest. However, no Dingy Skippers were seen in the Wordwell area this year. King’s – West of B1106 This area was only given a cursory check in 2011; none were seen. Annex E. White-letter Hairstreak – 2011 Following an excellent season last year, 2011 turned out to be a good year for most of the hairstreaks, and White-letter was again observed in 26 tetrads. The rolling five year count remains high at 79 (7∙2% of the whole county), which is strong for a UK BAP species that is declining in other parts of UK. It is worth noting though, that presence in one year does not necessarily indicate a stable colony; it can often be difficult to trace the source of an unexpected sighting, as the butterfly may simply be searching for a new home.
Trans. Suffolk Nat. Soc. 48 (2012)
BUTTERFLY REPORT 2011
141
The future of the White-letter Hairstreak in Britain is still viewed with concern because of the long-term consequences of Dutch Elm Disease. Yet it remains an under-recorded species that can be found in most places where elm survives – whenever intensive effort is put into a search. In Suffolk, it frequently turns up on elm in roadside hedgerows, where they are merely transient populations as distinct to well-established colonies. In other cases, they can re-appear at places where they have not been seen for a decade or more. Annex F. White Admiral 2011 White Admiral continues to hold its strong position in Suffolk woodlands. As noted last year, it has been noted in 78 tetrads (over 7% of the county) in the last five years, compared with just 13 (1%) in the 1983–1985 survey. The situation here is more favourable than in the UK as a whole, where its decline resulted in its being added to the UK BAP priority list in 2007. It inhabits damp woods with plenty of honeysuckle, and seems to have settled recently in several smaller woods that are not longstanding colonies. Climate change appears to have had a beneficial effect, and second generation emergences have been noted in good years (but not 2011). Progressive recording efforts have resulted in an increase in the tetrad count, but not all of the sightings indicate permanent colonization. Nonetheless, recent years have produced good numbers, and it is encouraging to have a UK BAP species doing so well in Suffolk. In 2011, White Admiral was recorded from 32 tetrads (4∙7% of the 677 covered) – not up to last year’s outstanding performance, but satisfying, all the same. Annex G. Grayling 2011 Added to the UK BAP Priority species list in 2007, the Grayling has lost 45% of its UK distribution over the past 30 years, and is now essentially a coastal species. Losses have been no less dramatic in Suffolk, and it is now very localised in its favourite Breckland haunts and extremely rare in Mid Suffolk, although it remains widespread in the Sandlings. The Grayling is an insect of dry sandy grassland, with a fondness for conifers on dry sandy heathland, and can still be found in the Brecks as well as the margins of Dunwich, Tunstall and Rendlesham forests. Formerly, it was regularly found in the general countryside too, but the clay soil of High Suffolk no longer supports it, and the distribution maps have thinned out, with few sightings outside of the prime areas of Suffolk Coast & Heaths District. The trend illustrated in recent years continues, and the colonies in the Brecks are isolated. In 2011 Grayling was found in just 7∙1% of the county, slightly less than last year. Numbers are holding up in the Sandlings, and this year the number spotted in the Brecks was up on last year. On the Cavenham Heath transect twelve were recorded - better than the worrying three of last year. Two new transects have been started by SWT in the Dunwich Forest, and both have Grayling populations; two were seen on Transect 1 and 32 on Transect 2.
Trans. Suffolk Nat. Soc. 48 (2012)
142
Suffolk Natural History, Vol. 48
Annex H. Wall Brown Survey: 2011 Results SNS/BC Single-species Survey The organized survey started by selecting 15 paired tetrads, one which had Wall records in the previous two years, paired with an adjacent tetrad with records from four or five years back, but none since. The idea was to get surveyors to find them flying in the primary good site, and then (ideally on the same day) to search the secondary tetrad in the hope of finding that they were still resident there too. Fifteen volunteers enrolled to provide cover of those squares, and some late additions extended the original plan with four extra unpaired tetrads. Inevitably, a few surveyors were unable to visit for various personal reasons, whilst many others recorded Walls without being allocated survey squares. A total of 55 people contributed records, from their own gardens, in a couple of cases. 2011 Results The bad news is that, for the second year in succession, not a single Wall was recorded from West Suffolk (TL tetrads). Five paired tetrads were thoroughly searched. Results for TM were also disappointing, with most sightings being close to the coast, and in known strong colonies. At least, the survey has improved our understanding of where the best remaining coastal habitat is still occupied. It appears that the Wall is only hanging on close to the sea or river estuaries, usually where unkempt grasses grow unmown on embankments and sea walls. The most westerly record was from Thorpe Bay on the Orwell estuary (TM2537), and the most inland was Bredfield (TM2753). The northern areas of Lowestoft and Gorleston (TG) were not target tetrads, but the Wall is holding on there relatively well. In all, Wall was recorded from 30 tetrads in 2011, as against 27 in 2010 – so the considerable extra recording effort produced mostly negative results, without the surge of sightings that might have been expected. Thirty four target tetrads were selected, and 30 of these were visited at least once, but four went unvisited. Only two primary “promising/strong� squares had Wall sightings. (but in neither case were they found both in 1st and 2nd generations). None of the secondary squares had any Wall sightings (all of these had Wall five or six years ago). The four extra unpaired squares were surveyed by volunteers joining after the main allocation, but none were seen in these squares either. The majority of sightings came in from roving recorders, plus a few from the Wider Countryside Butterfly Survey and the Big Butterfly Count. A total of 66 Wall records were noted, many from Shingle Street, Bawdsey and Boyton areas. A total of 30 tetrads had Wall records. Most sightings were of singles; the highest number seen together was six. This in itself reflects a declining population. The map below shows how coastal the distribution has become.
Trans. Suffolk Nat. Soc. 48 (2012)
BUTTERFLY REPORT 2011
143
Conclusion Was the 2011 survey a failure then? Far from it; the survey sadly confirmed that the Wall is moving east even faster than we already knew. Our objective now must be to identify the extent of the remaining colonies, with a view to preserving the habitat. Plans for 2012 Monitoring the Wall remains a priority, and recorders will continue searching in 2012. The survey will continue, but using different ground rules. Last year’s targets were clearly optimistic. So apart from checking two missed tetrads, there will be no set targets in TL in 2012. Infill targets will be set for coastal tetrads in TM and TG. Continued monitoring of last year’s TM targets will be welcome. In 2011, the butterfly deviated from its anticipated flight periods. There were early fliers in late April, low numbers in May but some into June; the 2nd generation started in late July rather than waiting for August, and there were only two sightings in September. The outcome was that it was possible to survey as planned in May and August and to miss them entirely. Intensified hunts with more repeat visits will be planned to tighten the net. 2011 Wall in 30 tetrads (4∙4% of 677) – and still none in TL (West Suffolk)
Trans. Suffolk Nat. Soc. 48 (2012)
Suffolk Natural History, Vol. 48
144
Coastal Work The Environment Agency has conducted a lot of coastal defence work during 2011, some of it disturbing good Wall habitat. In some cases, hopefully the EA work could prove beneficial in the long term. For the future, the preliminary Environmental Information Summary for the proposed East Anglia ONE offshore wind farm reveals that its undersea cables are likely to come ashore at Bawdsey - the site of one of our strongest Wall colonies. The Decline of the Wall over Successive Surveys The Decline of the Wall over successive 5 year periods Survey from to: Period Tetrads
1995 1999 5 yrs 1089
2000 2004 5 yrs 878
Wall
350
200
2001 2005 5 yrs 865
2002 2006 5 yrs 868
2003 2007 5 yrs 879
2004 2008 5 yrs 918
2005 2009 5 yrs 994
2006 2010 5 yrs 1003
2007 2011 5 yrs 1003
Tetrads from which Wall recorded 183
163
160
136
120
115
100
2006 1yr 557 44
2007 1yr 509 27
2008 1yr 549 28
2009 1yr 645 36
2010 1yr 575 27
2011 1yr 677 31
And for successive single years to 2011 Year Period Tetrads Wall
2003 1yr 449 83
2004 1yr 536 66
2005 1yr 500 39
Trans. Suffolk Nat. Soc. 48 (2012)
