by Bill Shreeves/font>

At last we have a memorable butterfly season to report on! With all the data collected on the Walks this can be more than a gut reaction. Using our normal performance criteria based around the percentage of species which increased by over 50% on 2002 or on their averages since walks began, we discovered that in 2002 only 8 species could be found which performed well. In 2003 this doubled to 16 species. Conversely in 2002 11 species were well down on either 2001 or their averages compared to only 5 in 2003. The colour coded chart for Dorset Butterfly Walks which Keith Powrie produces each year converts these statistics into visual proof. The 2003 chart dazzles the viewer with chunks of red & yellow, the colours representing species, which have done exceptionally well. The charts for previous years have been dominated by green & blue, the colours showing very poor performances.

The main reason for 2003 having been a better butterfly year was not, of course, a sudden transformation of the management of sites (would that were so!) but the usual vagaries of the British weather. Although in 2002 May had above average rain & June-July below average temperatures, August & September were warm & dry. This meant that late summer species had excellent weather for egg laying. The winter of 2002-2003, as measured by the Fontmell Magna weather station, followed the recent trend of being warmer & wetter than average. Computer predictions based on two decades of transect walk data seem to be suggesting that, on the whole this type of winter is beneficial to many species. On top of this promising foundation, 2003 from March to September was exceptionally dry and, save for May when temperatures were brought down by cold nights, was above average in warmth.

With such excellent summer weather any migrant species, which managed to cross to Britain, had a chance of establishing good second broods later in the summer. Table 1 shows that this did indeed prove to be the case. Red Admirals & Painted Ladies had their best year since the unforgettable summer of 1996.

The highest count on a walk for Painted Ladies came from Durlston East (222) with Lydlinch Common (210) not far behind. No Dorset walk failed to record a Painted Lady compared to 2 in 2002 and 11 which failed in 2001. Likewise every Dorset Transect Walk recorded Red Admiral with the highest at Melbury Down & Wood (322), where the late summer flowering of Hemp Agrimony sucked them in from a large area of North Dorset. AlthoughClouded Yellows had a slightly better year than in 2002 they were well below their great year 2000. Altogether 11 sites failed to record the species compared to 13 in 2002, 37 in 2001 and only 4 in 2000. Somewhat surprisingly the best count (45) came, not from Purbeck but from Deadmoor Common in the Blackmoor Vale. The coincidental combination of a big southward movement of Monarchs down the east coast of USA, thermals to take them to a high altitude, strong west winds to project them across the Atlantic and an airflow of at least 15 degrees centigrade to enable them to keep flying, did not take place in 2003. Consequently the only Monarch record for Dorset was a strangely late one at Gallows Hill on 12^th November (DBC web site). However, Dorset did experience its own mini migration of Long Tailed Blues. The first blue was recorded on 17^th August by Richard and Lyn Lambert near Corfe Mullen, and the second, at Ham Common by Ian Rabjohns and his son on the 26-27^th. Both were verified by excellent photographs. The recording of other Long Tailed Blues in Britain and also along the adjacent French coast makes it seem probable that these were not the usual emergences from imported vegetables but genuine migrants. On Portland migrants continued to be in evidence until late in the year with a Queen of Spain Fritillary observed at Southwell on 23^rd September & the last Painted Lady on 26^th October & Red Admiral on 3^rd December.

Table 2 shows that a record number of species attained Premier League status on the Transect Walks with over 50% increases on both 2002 & their averages since walks began.

The highest Small Tortoiseshell count came from the Stour Valley with 535. Lydlinch led the field with a total of 87 Commas. However the title of Dorset Butterfly of the Year must surely go to the Adonis Blue. As table 3 shows this has been an astounding year for the species. Just one transect walk on Fontmell Down on 15^th August by R.Wheeler brought a count of 959 (921 males & 38 females). To put this into perspective, this count, on just one day, exceeded the combined total for both broods, in any year, on Fontmell Down since walks began in 1980! Especially in North Dorset the dry summer helped to transform the good first brood into a second brood, which covered the downs in a shimmering vision of azure blue. Altogether 10 new km squares were recorded ranging right across Dorset from Cranborne Chase to Central & South Chalk, Portland & Purbeck. Totally new km squares for the species were: Watcombe Bottom (14.6. B.Bruce), Manor Farm near Sixpenny Handley (9.8. D.Chick), Compton Valence (26.8. L.de Whalley) & Mupe (30.8. S.Hayhurst).

The‘lucky fruit machine’ model explains very nicely why Adonis Blues covered so much downland, & even normally unoccupied north facing slopes, with a carpet of azure blue. 1) August/September 2002: second brood females need better than average warm weather & less than average rain; they get it; up comes an orange. 2) Winter 2002-3: Overwintering caterpillars need a mild winter; they get it (1.2 degrees Centigrade above average); a second orange. 3) Young caterpillars need early warmth to start feeding & to get their ant protectors on the move; again they get it (March & April, 2.2 & 1.1 degrees above average & rainfall below); a third orange & a good first brood emerges. 4) The new generation of caterpillars needs more warm & dry weather; again they get it with an exceptionally warm & dry June & August; a fourth orange & bingo an enormous record 2^nd brood! September 2003 was also dry but slightly below average in temperature…next year depends on whether more oranges come out of the fruit machine!

It is also gratifying to report that there were many species, shown in tables 4 & 5, which managed either to improve on their averages by over 50% or to exceed their 2002 count. The Small Blue had a good year in North Dorset with Melbury Down recording its highest ever total of 22. Off the walks there were 5 new records spread between Purbeck, Cranborne Chase & Central Chalk.

Manor Farm near Sixpenny Handley (28.5. D.Chick) & Southfields Hill (28.6 .J.Harris) were km squares where the species had never been recorded before. Badbury Rings (25.5.D.Hull) was the first record since 1940-69.

It must be admitted that for 4 of the species in table 5 their position was achieved via rather easy percentage rises from low bases or from single sightings on Transect Walks where they had been absent in previous years. The Dark Green Fritillary total Dorset count only staggered up from 160 to 184. Most of its position was due as usual to Melbury Down where the count of 133 represented a massive 72% of the total. The total Duke of Burgundy tally was actually only 38 compared to 46 in 2002. However the situation was at least a little healthier with Dukes re-appearing at the walks on Cerne, Powerstock Railway & Melbury Down. In addition there were 2 new records on sites in Cranborne Chase where it had never been listed before on any of the Dorset surveys. The White Admiral managed a Dorset total of 37 compared to just 14 in 2002 with only Fifehead managing double figures. However no less than 5 new sites were found in Cranborne Chase & another 3 in the North Heath Region, the latter including the first ever record on the Moors Valley Transect Walk. Although the Grayling pulled out of the worst of its 2002 slump this was very much confined to the South where the Purbeck chalk sites recorded growth from very low bases & Hethfelton Wood registered a record 73. The prize for the year’s most unusual record must go to an astonished Arthur Bryant who found a solitary Grayling on the Transect walk on the chalk at Cashmoor many miles from any other known colony. As if to prove there was no mistake, the proud butterfly actually obliged by sitting down next to its picture in the Butterfly book! At last, as shown in table 6, the Chalkhill Blue, has begun to show signs of recovery. Cerne Giant, Hod & Badbury all had counts above their averages. However Fontmell, Clubmens & Melbury Downs remained well down & only 22 appeared on all the Purbeck walks put together. The Small White was not a very popular high performer with the biggest totals at Cashmoor (483) & Durlston East (414).

Deadmoor had the highest count (351) in a good year for Silver Washed Fritillary & there were some outstanding Common Blue records led by Cerne Giant with 953. But perhaps the most gratifying results were for the Small Heath. Last year’s report pointed out that there had been a downward trend on the National Monitoring Scheme Transects since the start of the project in 1976 as well as some alarming extinctions on Dorset sites. 2003 saw a reversal with 78% of Dorset sites showing over 50% increases on 2002 & with only the West region of Dorset failing to show a similar increase on average counts. It was also of note that the gains were not just made on chalk down sites like Cerne Giant (903); heathland walks like Tadnoll (235) also shared in the bonanza. Further good news was its reappearance at Stubhampton Bottom & Kingcombe Stones & a recovery at Cashmoor from 9 in 2002 to 37.

Table 6 shows that the Small Pearl-bordered Fritillary was the only species, which improved substantially on 2002 but still remained well below its average count on walks. The situation for the Small Pearl continues to be alarming.

It was recorded again at Deadmore & reappeared at Powerstock but the numbers, as can be seen from Table 7, were depressingly small.

Better news came from Purbeck where a good colony was re-discovered on the golf course (18.6. K.Cook) & a possible new site on Bindon Hill (20.6. M.Warren). There were further scattered sightings on Hardown Hill but still no clear evidence of the location of a breeding colony.

As shown in Table 9, a further 3 species did not do particularly badly compared to 2002 but were well down on their average counts. It is possible that the cold May nights may have interrupted the emergence pattern of the Green Hairstreak. In spite of a poor performance over all, some sites like Hams Common (49), Cashmoor (35) & Upton South (34) still had good counts. Garston Wood even recorded its first ever Green Hairstreak on transect.

As can be seen from Table 12 the long hoped for recovery of Silver Studded Blue numbers has still not taken place. The fact that Studland is bucking the trend & recording high numbers suggests that many of the sites may be suffering from too much dense overgrown heather. Unfortunately this species is also falling behind in the Regional Action Plan surveys, which have found 34 sites occupied but have yet to visit 32.

The Wall has once again failed to recover lost ground. Although Table 13 shows slight increases in the number counted on both inland & coastal walks, the percentage of walks with at least one Wall seen has fallen to the lowest since 1995. The total recorded on all North Dorset walks was only 4 & in the East, 5. Rather more hopefully the Regional Action Plan survey still lists 92 sites with 44 of these on the inland areas of South & Central Chalk. Good news is that funding has been secured for research into the habitat & ecological requirements of the species to be supervised by Oxford Brookes University & Butterfly Conservation.

There were no species, which were well down on their 2002 totals. The nearest was the Holly Blue. In the South 67% of the sites were well below 2002, in the North & East around 40% & in the West none. As predicted in the 2002 report the upswing, which began in 2001, has come to an end before attaining the total coverage of all sites which was achieved in 1997-8.(see table 14). The Holly Blue in West Dorset did not continue to expand as had been hoped in the 2002 report but remained at a low count of 7 & came nowhere near to regaining the peak of 80, which it had attained in 1998.

Table 15 leads finally to the only species which qualifies for the title of lowest achieving Dorset butterfly of 2003, with over 50% of the walks recording it at least 50% below both 2002 & its averages, the Purple Hairstreak It must be admitted that this is rather a contentious result as this species is not well recorded on transects. However it could be argued that the real point is whether it is consistently recorded & there seems to be no reason why walkers would have suddenly started noticing fewer than in previous years unless there was a real change going on. The walk results do at least seem to back up the ‘gut feelings’ of many observers who have remarked on a general scarcity this year. Of course if there was a real change it might be related to alterations in feeding patterns, so that fewer butterflies came down to ground level than usual for example. On the other hand such a fine dry & warm summer might be expected to bring a larger proportion of butterflies down from the canopy to be counted? In 2003 only 28 were recorded on all walks compared to 93 in 2001 & 68 in 2002. Kinson Common had the highest count with 9. Hams Common & Langton Westwood had their first ever records. The summer of 2003 was dry & warm throughout most of the Purple Hairstreak flight period so perhaps more eggs were laid & 2004 will see an improvement?

The original reason for collecting Transect Walk data was for assessing the management of sites & for triggering off warning bells if things appeared to be going wrong. Many of the walks have now been running long enough for some very tentative conclusions to be made about the management of those sites, which have been walked for at least 6 years. A very rough yardstick would be the percentage of regular butterfly species on a site, which in 2003 were still below the average count since the walk began. It might be argued that the worst managed sites would have the largest numbers of species languishing below their averages. Only walks with over 5 years recording & no gaps in the data have been selected for this exercise & the results are shown in table 16 below. It can be seen that the average number of species in 2003 still below their all time walk averages, are fairly constant in the regions, ranging from the North, with 44%, to the West, with 53%. However there is more variation when the walks are grouped by habitat. In that case the Chalk Downs have the best performance with only 38% below compared to 56% for Woodland & 55% for Heaths. It is in the extremes of site performance within these groupings that there is most likely to be a management element. The worst woodland & over all site, Bracketts Coppice, with a massive 93% of species still below their average counts even after a good butterfly year, clearly needs to be carefully studied if the Dorset Wildlife Trust are interested in sustaining the biodiversity of their butterflies & probably also of other less known insect groups whose habitat requirements may be similar to the butterflies. At the other extreme is Cerne Giant, best over all & best chalk down site with only 14% of its species still below their averages. Clearly the managers of this site must be doing something right! Since all sites have very different local weather, aspect & altitude, too much must not be made of these statistics (this is not intended to be a naming & shaming exercise along the lines inflicted on hospitals & schools!) but they can be used as a rough guide line & to signal possible warning bells for the managers concerned.

As usual this report has only mentioned a small part of the data, which has been received from numerous garden recorders, km square bashers, Regional Action Plan surveyors & Transect walkers. 53 full sets of Walk records have been assembled including two new walks, at Lankham Bottom (the new Butterfly Conservation Reserve) and at Hogcliffe Southfield (English Nature NNR). Between 2001-3 the Regional Action Plan surveyors have found 753 sites for the priority butterfly species and have a further 301 to check before the completion of the 5 year project in 2005. Altogether, in 2003, 75 new km squares were discovered for the rarer species, which were not shown in the 1995-99 Millennium survey. My thanks to all recorders & data inputters and not least to the late Jim Harris who played a leading role in uncovering new sites & checking old ones in the remoter areas of the Central & Southern Chalk regions. I am especially grateful to the Regional Action Plan Co-ordinators who have worked hard to get this project up and running and to John Messer who retires after valiant service as joint co-ordinator for the West Dorset Coast. I must also pay tribute to Stephen Brown for taking over the Computer part of the recording operation when Bernard Franklin’s work took him out of Dorset & to David Jeffers for his thorough & efficient validating of all the records to a standard high enough to hand over to the Dorset Environmental Record Centre. When you read this there will hopefully still be a few months of the 2004 season left to complete the final year of the Supplementary Millennium Butterfly Atlas so please get out and do y our duty in as many of Dorset’s 2,6996(?) km squares as you can manage!