Survey Report 2016
In 2016 a large number of volunteer surveyors took to the disused quarries, cuttings and brownfield sites of county Durham to track down the rare dingy skipper butterfly. Surveyors experienced what can only be described as some challenging survey conditions, with below average temperatures and reduced sunshine hours; a bad combination for butterflies. Reports and sightings still streamed in though (a bit like the weather!), a summary of the results for Durham Wildlife Trust nature reserves and wider Durham sites is presented below.
A need for survey
A small, inconspicuous, brown and grey butterfly, the dingy skipper butterfly has declined nationally by almost 50% in recent decades. It receives no legal protection in England and this has contributed to a number of important sites being lost in the North-east.
A previous survey conducted in 2003/04 identified 108 inland colonies of the butterfly and a further 10 on the Durham Coast. Of the previously known sites the 2004 survey revealed that 34% of colonies experienced extinction during the period 1995-2004. Of these sites where extinction had occurred, 31% of these had been lost to redevelopment and 23% lost to the lack of management of the species’ required habitat. Due to the current conservation status of the dingy skipper in Durham and across the UK, the 2016 survey set out to resurvey the 2003/4 survey sites to better understand how this butterfly’s population now fares in the county and prioritise conservation management.
The volunteers were asked to walk a zigzag route through areas of bird’s-foot trefoil and record the number of dingy skipper seen, the date, duration of the count, temperature, wind speed and the number of other butterflies which were spotted. The surveys took place between April and June (the butterfly’s flight period) and between the hours of 11am and 4pm of any day where weather conditions were deemed suitable; temperatures above 12 oC with some sun, or over 16 oC without sun.
The following were identified from surveys undertaken on Durham Wildlife Trust (DWT) nature reserves and wider Durham sites.
Presence of dingy skipper
In all, seventeen DWT reserves were surveyed. Of these seventeen, dingy skipper butterfly was known to be present on eleven at the time of the previous survey in 2003/4. Dingy skipper was still present on these eleven sites. There were no new records for the butterfly for DWT sites where it was absent in 2003/2004. Table 1 below summarises the 2016 survey data.
85 sites were surveyed in total in 2016 across the Durham, Northumberland, Tyne & Wear, and Teesside area. Sixty-five of these sites were known to be occupied by dingy skipper in 2004. Survey results suggest that by 2016 the butterfly may have been lost from as many as thirty-seven of the sixty-five sites that supported populations of the butterfly in 2004, a decrease of 43%. A selection of 20 sites results are displayed below in Table 2.
Butterflies are cold-blooded animals and without warm conditions, they are vulnerable to predation and disease. Without warmth they cannot fly, so during bad weather they have no choice but to wait for better weather. The weather for Durham, for the three months of the survey period is summarised below (Durham University Observatory, 2016).
April was a disappointing month, a slow start to spring. Mean air temperature was well below average, 49th equal lowest since 1850, the coldest April since 1989. It was the 17th wettest April in 167 years but only the wettest since the very wet April of 2012 (134.4mm). Sunshine was a little below average; the total amount of sunshine for the month was 122.5 hours; this was a difference from the average of minus 10.7 hours.
Following a disappointing April, May was a warm month, equal 29th warmest in 167 years. Minimum temperatures in particular were well above average; the mean minimum was equal 12th warmest since 1900. The best of the temperatures came early in the month with a welcome maximum of 22.2°C on the 8th. Rainfall was below average, but all long-period totals remain above average, the 6-month and 12-month totals especially. Despite lower than average rainfall, hours of bright sunshine were below average too, by nearly an hour per day, reflecting the predominance of cloudy conditions with a generally easterly air flow off the North Sea.
June was a disappointing month: average temperature and average rainfall and much less sunshine than usual. Daytime temperatures were below average but the reverse was true at night, no doubt because of the generally cloudy skies. It was not a wet month and half the days were dry. Sunshine was well below average, the 8th least sunny June on record since 1882. There were five days with no sun at all. There were 2 hours less sunshine per day than normal, but it was still much better than 2012 when Durham only received 72 hours of bright sunshine in June.
Only four surveys on DWT reserves were undertaken in temperatures under 14oC. Of these four, two returned positive results. These were Rainton Meadows where three butterflies were recorded at 13oC and Raisby Hill Grassland where six butterflies were recorded in temperatures of only 12oC. Out of the selection of non-DWT sites around half were undertaken in temperatures of less than 14 oC. Non were undertaken in temperatures less than 12 oC. Five records were submitted without temperatures.
Time spent searching
Time spent searching for the butterfly varied between sites. The longest search on a DWT site was at Blackhall Rocks. A large site, a number of population patches were found below the cliff tops, in total 14 butterflies were found with a time spent searching of 135 minutes. On non DWT sites a survey of Wingate Quarry lasted 3 hours and yielded 12 dingy skipper. A large former quarry site, this has historically had a large population of the butterfly. The shortest time searching where a dingy skipper butterfly was found was 10 minutes at Low Barns where two dingy skippers were found. Most searches lasted for at least 40 minutes. The average search time was 58 minutes.
Although this wasn’t a required record, many surveyors provided comment on vegetation structure. Table 3 below summaries this information and is accompanied with data DWT holds for sites and is compared to the highest single count for dingy skipper per site 2016. On non-DWT sites many surveyors were able to identify probable causes of extinction. Often, these involved redevelopment of brownfield sites, lack of management/vegetation succession and, occasionally, inappropriate management.
Out of seventeen Durham Wildlife Trust sites surveyed, eleven had dingy skipper present. These were sites where dingy skipper was also present in 2003, a 0% decrease. Of these eleven sites, seven sites recorded five or less individuals as a highest count. Whilst of the remaining four, three had a highest count of six, and one had a count of fourteen. The site with fourteen dingy skippers was Blackhall Rocks which was is a large site. Searching time was longest here, and a number of population patches were found.
The butterfly also fared well on nature reserves managed by Local Authorities and other conservation bodies, an example being Wingate Quarry. This suggests that an effectively-managed network of reserves and SSSIs will do much to conserve the species in northeast England.
The poor spring weather of 2016, led to a poor flight period for the butterfly. It also resulted in limited days when surveyors were available to be out in optimum survey conditions. Survey data reflects some surveys conducted towards the end of the survey period. The highest counts for sites that received more than one survey visit tended to be in the period late May (20th onwards) to early June (up to the 6th).
With this taken into account, counts were still low given the considerable amount of time surveyors spent searching. The average time spent searching was 58 minutes; plenty of time to attain data for population figures. When this data is considered against the habitat suitability of the sites for dingy skipper, a general conclusion would fit that grassland structure is becoming unsuitable for dingy skipper on the sites where it was found in 2003. Whilst on the sites where it was not present both in 2003 and 2016, the habitat is not suitable or if suitable (in the case of Milkwellburn Wood North) extremely isolated and small.
On sites which are suitable but where low counts were recorded (Bishop Middleham Quarry, Trimdon Grange SSSI), it should be recognised that further survey work should be conducted in 2017 under better weather conditions.
Bishop Middleham Quarry SSSI has been monitored as part of the UK Butterfly Monitoring Scheme. Long term trends for the dingy skipper on Bishop Middleham Quarry SSSI has shown an upward trend in population for this site since recording began. 2016 however had the second lowest record since recording began in 2003, whilst in 2015 the second highest population was recorded for this site. This may reflect concerns over the suitability of survey conditions as opposed to habitat condition, which currently on the whole appears favourable on this site.
Survey results suggest that by 2016 the butterfly may have been lost from as many as thirty-seven of the sixty-five sites that supported populations of the butterfly in 2004, a decrease of 43%. This result, compared to that from the earlier survey, suggests that the attrition rate of dingy skipper colonies remains extremely high and may actually be accelerating.
An extension to a known population was that at Coxhoe quarry where sixteen butterflies were found on restored spoil leading down to the Raisby Way; An indication of the importance of the correct guidance and governance of quarry sites can play in the conservation of this rare butterfly.
Many surveyors were able to identify probable causes of extinction. Often, these involved redevelopment of brownfield sites, lack of management/vegetation succession and, occasionally, inappropriate management. In a small number of cases, the butterfly’s status could not be confirmed due to poor weather during surveys.
It seems that the species is likely to increase in rarity due to the persistent losses of non-reserve sites. Results indicate that whereas sites designated as SSSIs tend to retain the species, those designated as CWS/LWS fare less well and often experience partial or total loss of breeding habitat to development or to vegetation succession arising through lack of management.
Results also suggest that greater attention should be paid to the quality and long term management of sites where habitat creation or translocation had been undertaken to mitigate habitat loss to development. Surveys were undertaken at five such sites (Brusselton Hill, Simpasture Junction, Shildon Railway Museum, Path Head Quarry and A181 Wheatley bypass). The butterfly is presumed extinct at the first two sites where vegetation is now rank and scrubby while a bank of railway spoil at the Museum upon which suitable habitat was developing in 2004 has been subsequently capped with topsoil and seeded with lawn-type grasses. Although no dingy skippers were seen at Path Head Quarry (the survey was probably undertaken too early) the habitat remains suitable; in this case, the site is managed annually by its owners under the direction of Butterfly Conservation. The Wheatley bypass on the A181 retains its population of dingy skippers although numbers are much reduced from twelve years ago, probably as a consequence of increased grassiness and development of scrub.
Thank you to everyone who took part and contributed toward the success of this survey.
Mark & Dave