2009 Butterfly Report

Rob Parker

After two poor years, 2009 came as something of a relief. For most species, it has been a decent season, and the major immigration of Painted Lady was very welcome. Only for a few species has it been a poor year, and long-term declines account for some of these. Good recording effort has resulted in meaningful coverage for the whole of the 5-year period.

Weather. The winter was colder than recent mild years, and even below average judged by historic averages, with February bringing frosts, cold winds and snow. In all, air frosts occurred 38 times in East Anglia. Thereafter, things improved, and 15th March was warm enough to bring out first butterfly sightings for many observers. Spring was warmer, sunnier and drier than 2008. The summer figures in the table below are averages, and mask the reality that July was very wet (15 rainy days), whereas August and September were unusually dry, creating conditions of drought for some larval host plants.

The shortage of sunny April days with temperatures of above 16°C (at the SNS weather station in Boxford) again explains why transect walkers had difficulty in getting any walks in within the stipulated weather criteria. May was slightly better, but there were still 12 days that failed to meet the basic butterfly flight criteria, delaying the emergence of species that had passed the winter as pupae. In June there were 13 days that provided little opportunity for flight, or pairing. The frost and snow of December (the coldest December for 15 years) will be bad news for some species, particularly over wintering Red Admirals. However it could also kill parasitic fly and wasp species, once again bringing benefits for host species next year.

Monitoring the BAP Species. There are now 5 Suffolk BAP priority species, and 2 in a new category of “for study only ” .

The annual Silver-studded Blue count missed the peak at several of the major sites, but numbers were generally close to 2006 levels. A professional ecological survey was conducted by Neil Ravenscroft, and provided useful data for conservation at our most threatened sites. The translocated

colony at Blaxhall Common survived another season, and up to 21 butterflies were recorded on the transect, flying over a five week period. For the fourth year in succession, the Dingy Skipper was not found at RAF Barnham,

and the colony has probably been lost. Again, there were no sightings from the small isolated site at Center Parcs, and this too may have been lost. In the King’s Forest, the habitat is in transition, with decent numbers breeding only at the archery site, so the overall picture is gloomy.

White-letter Hairstreak was one of the species that was hard to find in 2009, partly because of July ’s wet weather. In the period 2005 to date, it has been found in almost 8% of the county ’s 1088 tetrads, but it was seen in only 2.5% of the tetrads surveyed in 2009.

White Admiral continues to do well in Suffolk woodlands. This year, it was noted in 26 tetrads (4%) compared with 13 (1%) in the whole of the 1983-85 survey. The situation here is more favourable than in the UK as a whole.

Grayling is in general decline across Suffolk, but enjoyed a good season at several coastal sites, particularly at North Warren. Its present distribution is restricted to well-drained sandy soils of low fertility, where sparse grassland is found, mainly in the Brecks and the Sandlings.

The UK BAP species list includes 2 further species for enhanced monitoring. In both cases, the larval host plant is grass:

Wall is in decline in the UK and in Suffolk. Lost from inland locations, its distribution is now restricted to well-drained sandy soils of low fertility, particularly down the east coast, with a lesser stronghold in the NW corner of the county. In 2009, it was found in 5.6% of the surveyed tetrads, against 12% over the past 5 years. Small Heath is in a less critical situation than the Wall, but is losing ground on farmland amongst fertilized grass. It has been recorded from 234 tetrads in the past 5 years (24% of 994 recorded tetrads), but numerical counts are falling at the few transect sites which still support it.

Residents-Winners&Losers. Some of our resident species had an encouragingly good season. In particular, the Small Tortoiseshell made quite a come-back, being the season’s first sighting for many recorders, along with Peacocks, Commas and Brimstones, mainly during a bright spell in mid March. Partly this was due to an immigration of healthy Small Tortoiseshells over wintering successfully after their arrival in late August 2008, probably enhanced by reduced parasitism from the Tachinid fly Sturmia bella, which suffered losses during the colder winter. The good showing of Vanessids and Whites in gardens, along with immigrants, left an impression of abundance that was not valid for all species. The Common Blue & Brown Argus, both recovered after poor seasons in 2007/8. Small Copper numbers were average, whilst Holly Blue appeared to have begun one of its periodic downturns, with a poor showing in the second generation. Small and Essex Skippers maintained their distribution but were not particularly abundant, whereas the Large Skipper had a better than average year. The commoner Browns all had a good year, particularly the Speckled Wood. The less mild winters have checked the surge of the Red Admiral somewhat, but it was present everywhere, and was still flying into December, albeit in small numbers.

Purple Emperor. The introduced Purple

Emperors were still flying, not only in Theberton Woods, but also putting in an appearance at Minsmere. A male was photographed from the RSPB’s canopy hide on the 19th July and was much observed until the 23rd July. Perhaps this heralds a spread to the wider area of sallow lined ditches between the two sites. One possible female sighting at Minsmere was not confirmed by photography. A separate Purple Emperor sheltering from the rain in Bury St Edmunds is more difficult to explain.

Migrants. 2009 was an interesting year for migrants and other unusual observations. A few isolated Painted Lady sightings in mid May were overtaken on 23/24/25 May by a major immigration, first evident along Suffolk’s east coast, but occurring simultaneously along the entire south coast of England too. Classic streams of migrants flying determinedly northwest at shoulder height were counted at over 100 per hour in many hotspots, particularly along our river valleys. The butterflies were worn and faded, and climbed up over trees or houses, before descending again, and continuing without pausing for nectar. The event was monitored and recorded in real time, on-line by Butterfly Conservation’s Migration Watch. During that influx, there were very few mentions of other butterfly species, but Hummingbird Hawkmoths arrived too, and later in the season small numbers of Clouded Yellows. In the days following the main Painted Lady influx, it appeared that most had flown beyond Suffolk, but some paused for nectar and egg-laying on thistle. The Clouded Yellows mostly paused to lay eggs on coastal clover patches. The resultant generations put Painted Lady in most Suffolk gardens in July, and selected coastal locations had Clouded Yellows in clusters in September. Both species continued to fly right through October and into a mild November. By the end of the season, Painted Lady had been recorded from 69% of tetrads visited.

Vagrants & Unusual Sightings. July brought three separate sightings of Marbled White. One singleton was seen near the Cambs border at Kirtling, another in the Fynn Valley, and the third in the King’s Forest; all were flying in suitable looking grassland habitat and identified by reputable observers. Marbled White has been making progress in Cambridgeshire recently, and it is likely that climate change is extending its range. At least 3 Silverwashed Fritillary were unexpectedly seen in a private wood near Stowmarket in July. An optimistic explanation might be to hope that they arrived with the Silver-washed expansion in 2006, and have been breeding ever since. No such interpretation can be put on the two Tiger Swallowtails from North America (Papilio rutulus) that turned up in Long Melford and Sudbury in September. These were in local gardens, and must have been releases. An unexpected female Longtailed Blue probably arrived as a stowaway in imported peas.

Early & Late Records. Following a cooler, more “normal” winter, spring 2009 did not bring any earliest-ever records. Thereafter the season was of a stop-go nature, with alternating drought and heavy rain, followed by a mild autumn and a particularly gentle November – but still without any latest-ever records.

Geographic Coverage. As the final year of the five-year period, 2009 brought a challenge to extend cover from 80% by filling the unvisited “black holes” , and many recorders rose to the challenge. A record total of 645 tetrads were visited, bringing overall cover up to 91% of the county during the 5-year period. This honourable achievement looks perfect when measured at the 10km square scale required for the national records. The area covered most thinly is the agricultural land in High Suffolk, where both the human population and the butterfly density are inherently low. Improving cover in this area sets a challenge for the future, as there must be some pockets of decent habitat that remain undiscovered.

Species Maps. Distribution Maps for individual species have been prepared for our 31 regulars, and these are available for reference as required. This year’s total species count stands at 34, including the introduced Purple Emperor, but excluding the Long-tailed Blue and the Tiger Swallowtails. The average number of species recorded per tetrad was 10.3, the highest annual figure since the start of the Millennium survey.

Transects. Any analysis derived from distribution maps and counts of presence/absence responds rather slowly to changes in a species’ health. The “index” derived from transect walks, on the other hand, gives a valid evaluation of a species’ abundance in the current year, providing a more sensitive indicator of change, albeit at specific sites. The 16 full transects walked this year did reflect falling numbers of Common Blue and Brown Argus, with a longer-term decline of several other species including Grayling and Small Heath. Special thanks are due to all our transect walkers for their commitment to regular monitoring at: North Warren (Rob Macklin), Fynn Valley (Richard Stewart), Minsmere (Robin Harvey), Bradfield Woods (Steve Hunt), Center Parcs (Graham Hersey-Green), Cavenham Heath (Michael Taylor), Walberswick (Will Russell), Spring Lane (Rob Parker), Combs Wood (Liz Cutting), Ramsey/Hintlesham and Wolves Wood (Mark Nowers), Newsons Farm (Frances Bee), Upper Abbey Farm (Trudy Seagon), Alton Water (Simon Waters), Manor Farm (Brenda Hudson) and Tythe Farm (Peter Vincent). 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.

Essex Skipper by Beryl Johnson