Worcestershire Record No. 20 April 2007 pp. 11-15

BROWN HAIRSTREAK ON THE MOVE

Mike Williams

A pair of Brown Hairstreaks, male on the left.
Picture Gerry Kendall of Upper Thames BC

For those who enjoy a good detective story the unfolding tale of Worcestershire’s Brown Hairstreaks has much to commend it. Like many of the Hairstreak family of butterflies, the adult Brown Hairstreak can be surprisingly elusive spending much of its days high in the canopy only descending rarely in search of nectar. This is particularly the case with the males which are considered to use assembly trees, mainly prominent ash trees, where they congregate after emergence and where breeding takes place. Most sightings, in fact, are of females which can occasionally be spotted around the sloe bushes on which it lays its eggs. Even then it is often hard to spot, because for much of the time the butterfly crawls around its host food-plant in search of the perfect spot to lay its egg, usually low down at the base of a spine. These small, white bun-shaped objects remain on the blackthorn throughout the winter months and with practice are relatively easy to spot; indeed, most of our current knowledge of the distribution of the Brown Hairstreak in Worcestershire is based on finding eggs rather than records of adult sightings.

Always apparently rare in the county, there are relatively few reports in the literature and not many surviving specimens in museum collections either. The earliest reference I can find is in Hastings who in 1834 lists Trench Wood as a location, and there are specimens from the same location in Worcester Museum dated 1856. Trench Wood was clearly the favoured location for finding the insect in Victorian times although, intriguingly, there is a specimen in the Rothschild collection in the British Museum labelled Pershore 1891. The only references away from east Worcestershire came in 1899 when two leading Malvern lepidopterists of the day mention Eastnor, Birchwood and Cowleigh as localities, with the latter location being repeated in the Victoria County History of 1901, together with Wyre Forest. From this point on, records of Brown Hairstreak in the county come to an apparent end and for much of the 20th century the butterfly was believed extinct. It was only after some painstaking research by the late Jack Green, County Recorder for Lepidoptera for many years, that the Brown Hairstreak was rediscovered in April 1970 at Grafton Wood east of Worcester, now a nature reserve owned by Butterfly Conservation and the Worcestershire Wildlife Trust. Our current knowledge of the butterfly in the county dates from this point.
Three Brown Hairstreak eggs (singles are more usual).
Picture Trevor Bucknall
Brown Hairstreak larva

Nationally, the Brown Hairstreak is a UK Biodiversity Action Plan species and is listed as a species of conservation concern. It typically breeds over wide areas of countryside, mainly on farm hedges or blackthorn within or near woodland, and generally on low lying heavy clay soils such as those that occur in east Worcestershire within the former Forest of Feckenham. Although formerly occurring across most of England and Wales, it has declined substantially across much of its former range. Recent surveys suggest that the butterfly’s UK distribution may have contracted by as much as 35% over the past 20 years and it has been recommended that in BAP terms it should be now viewed as a priority species. This decline is associated with agricultural intensification, particularly hedgerow removal and increased hedgerow management. While years ago, many farm hedges were laid or cut on rotation, this has largely been replaced by annual management. Equally, the trend towards arable farming has seen an increase in field size and the removal of many hedgerows or their reduction to neat clipped boxes. Because the species over-winters as an egg, it is particularly susceptible to annual flailing of hedgerows which usually occurs during the winter months. Previous studies elsewhere in the country have suggested that up to 80% of all eggs are lost as a result of annual trimming. Changes in woodland management over the last century are also likely to have had a negative impact with the ending of coppicing reducing the frequency of sunny open areas within woodland where blackthorn might flourish and provide ideal laying conditions. The net result of these changes has meant that populations of the Brown Hairstreak have been significantly reduced and surviving colonies, such as that in Worcestershire, therefore assume high conservation value. The butterfly now has its own Species Action Plan included in the county Biodiversity Action Plan and is seen as a priority species. It has now disappeared from all surrounding counties and, outside of Worcestershire, the nearest surviving Brown Hairstreak colonies are to be found in Wiltshire, Oxfordshire and Lincolnshire.

The rediscovery of the Brown Hairstreak in the county led to a number of conservation initiatives which have continued to be refined and developed over the past 30 years. In 1971, Grafton Wood and some of the surrounding farmland was designated a Site of Special Scientific Interest which has helped to maintain the key area for the butterfly and has provided a springboard to continuing monitoring and conservation management. Much of our current knowledge of the Brown Hairstreak in Worcestershire stems from the winter monitoring of eggs. The habits of the butterfly does not lend itself to normal monitoring methods such as the transect recording of adults used for most species and really the only way to determine fluctuations in populations of the butterfly and assess the impact of management is by counting eggs. Worcestershire data goes back to 1970 and constitutes what must be one of the longest running datasets on any species of Lepidoptera in the UK. Monitoring is mainly focused in the immediate area of Grafton Wood and, in the early years, figures were generally low with even zero counts in a couple of years

BROWN HAIRSTREAK EGG COUNTS

Core area counts (hedgerows A-G)

Winter season

Number of eggs found

69/70

30+

70/71

16

71/72

1

72/73

7

73/74

0

74/75

6

75/76

-

76/77

0

77/78

5

78/79

11

79/80

27

80/81

7

81/82

27

82/83

35

83/84

-

84/85

-

85/86

35

86/87

93

87/88

50+

88/89

27

89/90

30

90/91

39

91/92

91

92/93

365

93/94

188

94/95

391

95/96

71

96/97

149

97/98

57

98/99

83

99/00

65

00/01

88

01/02

392

02/03

216

03/04

191

04/05

408

05/06

253

From 1990 onwards, the count has been undertaken by volunteers from the West Midlands branch of Butterfly Conservation and has been organised on a more systematic basis. Each section of blackthorn within the core area has been given a reference letter and allocated a specific search time which is expressed in person hours. The idea is for the same amount of monitoring effort to be given to each section each year in order to achieve some consistency of data. As well as the number of eggs, data has also been collected on the height at which eggs have been laid and whether eggs have been laid singly or in clusters of two, three or more. The results (see table) show that most eggs are laid singly and there is a noticeable drop off in the number of eggs recorded once blackthorn reaches over four feet in height (usually 3-4 years in age). Young, mainly south facing blackthorn is strongly favoured for egg-laying, either leading shoots growing out of the hedge or suckering blackthorn at the hedgerow bottom. Much of the blackthorn within the core area takes the form of thickets along the edge of the wood which, if unmanaged, would quickly become overgrown and unsuitable. Using our egg data to guide management, from the early 1990s onwards sections of blackthorn within the SSSI have been coppiced on approximately a four year rotation. By increasing the amount of blackthorn in ideal condition for ovipositing, this has had a major impact on the number of eggs recorded, with generally high counts over the past ten years including a maximum count of over 400 eggs in 2004/5. Typically, counts on individual sections cut have peaked 2-3 years after management and numbers have then declined only to increase again after the next coppice rotation.

HEIGHT AT WHICH EGGS LAID ON BLACKTHORN AND NUMBER OF EGGS EACH YEAR

Height in feet

Year

99/00

Year

00/01

Year

01/02

Year

02/03

Year

03/04

Year

04/05

Year

05/06

0>1

33

8

111

97

108

131

136

1>2

51

40

170

139

152

192

146

2>4

35

121

209

154

138

341

165

4>4.5

3

33

76

39

34

70

38

4.5>6

4

14

93

19

7

55

18

6 & above

0

1

26

1

0

9

0

               

EGG GROUPINGS

Single

111

192

551

237

389

637

326

Double

7

13

52

36

24

63

29

Treble

0

3

5

7

1

7

5

Quads

0

0

0

1

1

2

3

Quins

0

0

0

1

0

0

0

               

STANDARD SEARCH TIMES FOR EACH CORE HEDGEROW

Core hedge

Number of eggs found each year

A 4.25

Hours

17

36

129

57

44

27

43

B 1.5 hours

1

11

46

12

14

74

40

C 1 hour

0

3

19

16

14

35

9

D 2.5 hours

4

5

22

28

16

88

39

E 2.5 hours

5

13

19

39

9

65

70

F 2 hours

0

4

24

53

43

29

16

G 3.5 hours

38

16

133

11

51

91

36

Total eggs

65

88

392

216

191

408

253

Having achieved the first objective of gaining a better understanding of the ecological requirements of the butterfly and having laid the basis of good management within the Grafton Wood SSSI, it was time to begin the next chapter of discovery. Just how widespread was the Brown Hairstreak in east Worcestershire? It was time to find out. During the winter of 1993/4 a survey was carried out, with financial support from English Nature, of hedgerows and woodland within the triangle of Grafton Wood, Hill Wood and Quartern Ash Wood. This proved in many ways a depressing experience. Hedgerows generally had been subject to rigorous trimming which had often reduced the height of the hedges to only a fraction of their pre-cut size. In some instances, there was evidence of whole hedge removal while, in other cases, hedges had been reduced to just a few inches from the ground. Nevertheless, eggs were found and by the end of the survey we were able to report that presence of the butterfly was confirmed in no fewer than 16 1km squares suggesting a wider distribution in the county than had been previously assumed. Furthermore, the survey suggested that the potential range of the butterfly was considerably greater but that generally unsympathetic hedgerow management was proving a major constraint.

Severely Flailed hedge. Such flailing can destroy many Brown Hairstreak eggs.

In order to address this issue, the decision was taken the following year to try approaching local farmers to encourage them to join the Hedgerow Incentive Scheme which had been recently launched as part of Countryside Stewardship. The scheme offered payments to landowners for the restoration and sympathetic management of hedgerows. In practice, the financial incentives offered proved unattractive to farmers and, although some useful contacts were made and a number of landowners expressed interest in the Brown Hairstreak, none were persuaded to enter the scheme. A useful by-product of this work, however, was the preparation of a glossy leaflet which was aimed at promoting awareness of the Brown Hairstreak butterfly and providing management advice. The leaflets were provided to MAFF and also FWAG officers for local distribution and have since been reprinted.

Over the years, as time allowed, we continued to build up our knowledge of the distribution of the butterfly and by the beginning of 2004 we had recorded the butterfly in 37 1km squares (see map). Grafton Wood was still very much the centre of the butterfly’s distribution but, by now, we had found eggs as far north as Bradley Green, Naunton Beauchamp to the south, Inkberrow in the east and Earls Common to the west. In fact, 2004 proved to be quite a year of advancement for the Brown Hairstreak in Worcestershire. The appointment of Butterfly Conservation’s first regional staff the previous year had led to renewed efforts to engage with landowners and the local community in general. Contact with DEFRA, who had now taken on responsibility for the revised Countryside Stewardship scheme, proved invaluable and, for the first time, there was a means by which our egg data could be fed directly into management prescriptions on farmland. DEFRA staff agreed to consult Butterfly Conservation on all farm agreements and input our data onto their own GIS system. A joint training event attracted over 40 farmers who learned firsthand about the requirements of the Brown Hairstreak and Countryside Stewardship. Parallel to this, a successful application to the Lottery’s Awards for All scheme meant that a concerted effort could be made to involve the local community. New display boards were ordered and an interpretation panel was erected at the entrance to Grafton Wood nature reserve. Perhaps most significantly, a local Brown Hairstreak champion scheme was launched whereby local residents were invited to become involved in recording the butterfly and planting blackthorn on their own land. A regular email newsletter was started to keep people in touch with the latest sightings and a number of public events and activities were arranged. All of this was translated into increased recording effort so that by Spring 2005 the number of 1 km squares in which eggs had been discovered had grown to 54.

This upsurge in recording has continued during this current winter (2005-2006) and the number of known squares has now incredibly topped the hundred mark. For the first time, an egg has been discovered across the border into Warwickshire (the first record there for over thirty years) and eggs have been found in Trench Wood which is the first confirmed record of breeding at this site in over a hundred years! 

The two maps show the present known distribution of Brown Hairstreaks in Worcestershire, based on 1 km squares. The first map shows the VC37 boundary; the second is an enlargement. Yellow dots show records from 1990-2004, green dots additions in 2004-2005, and red the additions in 2005-2006. Maps prepared by John Partridge using DMap

Like all detective stories, however, there are still many questions still to be resolved and even aspects of the butterfly’s life cycle are still not properly understood. This includes issues like the butterfly’s use of assembly trees. This is something that we have only just begun to study over the past two years. So far only a few trees have been identified, mostly hedgerow Ash trees but also prominent trees at the edge of woodland, and it is still uncertain whether the same trees are used consistently every year or indeed whether male butterflies remain loyal to the same tree throughout the flight season. There is also the mystery of pupation. Although a number of larvae have been followed over a period of weeks and we have been able to challenge the previously held view that caterpillars are only active around dusk, we have not so far been able to locate pupae. Opinions seem to differ as to the exact pupation site as so few have been found. On the ground within leaf litter or even below the earth seems most likely and it may be that, like the Purple Hairstreak, the pupa is associated with ants’ nests.

A 'master' or assembly tree. Ash discovered in 2005 by observing Brown Hairstreaks in the tree top using a bird-watchers' telescope.

Perhaps the most fundamental question, however, is whether what we have seen particularly over the past two years in terms of new records is just a reflection of increased recording effort or represents a genuine expansion of range? It is difficult to be sure and probably the answer is a bit of both. Certainly, the local Brown Hairstreak Champions scheme together with the Vision Mapping project of the Worcestershire Biodiversity Partnership has recruited new recorders who have been trained and encouraged to search for eggs. It is also true that we have looked for eggs in areas where we would not even have considered looking five years ago and, each time we have been successful, it has encouraged us to widen our search area still further. I would like to feel, however, that the good management around the core area of Grafton Wood and nearby woods has helped to build up population numbers in a way that has aided dispersal. As far as the wider countryside is concerned, there is still a long way to go before Hairstreak-friendly hedgerow management becomes the norm but there is no doubt that our partnership with DEFRA particularly on the back of the new agri-environment scheme is bearing fruit and we are seeing increasing numbers of landowners joining the scheme. The new entry level stewardship scheme encourages rotational cutting of hedgerows while higher level stewardship includes specific management prescriptions for Brown Hairstreak which have been developed in association with Butterfly Conservation. This includes trimming each hedge in rotation no more than one year in three, allowing hedges to reach and maintain a minimum height and width of 2 metres, planting up gaps with at least 50% blackthorn and leaving a 2-6m wide margin alongside the hedgerow. Although primarily designed to benefit the Brown Hairstreak there is no doubt that many farmland birds, hedgerow plants and other insects will also gain from these changes.

Another training day in January 2006 held jointly with the Worcestershire Biodiversity Partnership attracted a further 25 local landowners to learn more about the new stewardship schemes. Already one of the farmers attending has been in touch to say he has found Brown Hairstreak eggs on his land and to ask for management advice. All this is excellent news, as is the announcement in the latest Worcestershire Wildlife Trust newsletter that the Forest of Feckenham has been designated as a priority conservation area within the county, which makes it the focus of future conservation action and land acquisition. The butterfly has now been recorded on five Trust reserves, including the new reserve at Humpy Meadows, within the area which is a good start. The Brown Hairstreak is very much the flagship species for this landscape based approach within the Forest of Feckenham as it is principally a farmland species dependent on a network of woodland, with interconnecting well managed hedgerows and herb-rich grasslands, if it is to thrive. There is no doubt that if we can improve its status through better hedgerow and woodland management, there will be benefits for many other forms of wildlife. This is an exciting project with lots of challenges but we have made a good start and Butterfly Conservation will be continuing to work closely with the Wildlife Trust in the months ahead to turn this vision into reality.

Undoubtedly, there are more locations for the Brown Hairstreak to be discovered and we are keen to encourage further recording. It would still, however, be a big surprise if there were modern records outside of a line joining Worcester-Pershore-Evesham-Redditch-Droitwich-Worcester but it would be nice to be proved wrong! Jack Green in his little booklet on Worcestershire’s butterflies lists the 10km squares SO84 and SO94 (both outside the current known range) as holding the butterfly but gives no further detail, although in his subsequent article for the Entomologists Record he refers to eggs being found at “a perimeter dispersal point on a disused airfield”! It is clues like this that help bring out the detective in all of us. If anyone is interested in finding out more, helping with future recording efforts or would like to be kept up to date with the unfolding Brown Hairstreak story via the email newsletter please get in touch.

References

ASHER J, WARREN M, FOX R, HARDING P, JEFFCOATE G & JEFFCOATE S. 2001 The Millennium Atlas of Butterflies in Britain and Ireland. Oxford University Press.
BARKER Simon. 1995 Brown Hairstreak Conservation Project: Hedgerow Management Initiative. Unpublished report to English Nature and Butterfly Conservation (West Midlands branch).
BARKER Simon, WARREN Martin, WILLIAMS Mike, & DAVIS John. 1996 Hedgerows for Hairstreaks: Hedgerow and woodland management to conserve the Brown Hairstreak butterfly. Butterfly Conservation leaflet
EDWARDS W, & TOWNDROW RF. 1899 The Butterflies and Moths of Malvern
ELLIS, Jane & WILLIAMS, Mike. 2005 Brown Hairstreak: you can help save it! Butterfly Conservation leaflet 2005
GREEN J E. 1982 A practical guide to the Butterflies of Worcestershire. Worcestershire Nature Conservation Trust 1982
GREEN, J.E. 1990 The History, Ecology and Habits of Thecla betulae in Worcestershire. Entomologist's Record and Journal of Variation, 102, 253-256
HASTINGS Charles. 1834 Illustrations of the Natural History of Worcestershire
MABBETT Rob & WILLIAMS Mike. 1994 Brown Hairstreak in Worcestershire. Unpublished report to English Nature
POLLARD, E. 1977 A method for assessing changes in the abundance of butterflies. Biological Conservation, 12, 115-134
TAYLOR Marjory. 2005 Introduction to the new agri-environment schemes. Action for the Brown Hairstreak: sharing good practice. Proceedings from Butterfly Conservation seminar
THOMAS Jeremy. 1974 Factors influencing the numbers and distribution of the Brown Hairstreak and Black Hairstreak unpublished Ph.D. thesis
THOMAS Jeremy & LEWINGTON Richard. 1991 The Butterflies of Britain & Ireland. National Trust & Dorling Kindersley
VICTORIA HISTORY OF THE COUNTY OF WORCESTER 1901
WORCESTERSHIRE WILDLIFE TRUST Worcestershire Wildlife News No. 104, Jan 2006
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