Hengistbury Head Butterfly Census Annual Report 2019 Written by Venetia Powell There are around 59 species of butterfly present in the UK according to the UK Butterfly Monitoring Scheme (UKBMS); 25 of these species have been recorded around Hengistbury Head. The number of species in the UK are monitored in order to be able to assess and keep track of the change in climate. UKBMS are able to monitor climate change using the populations of butterfly and by looking at the living conditions of specified areas (habitats) and whether the populations increase or decline. For example, butterflies do not cope well in cold temperatures and therefore thrive more in warmth; they are more likely to seek shelter in colder climates to be able to restore their optimum body temperatures. This is because butterflies are cold blooded, meaning that they are unable to produce their own heat and therefore, would lack the energy they need to be able to fly. To be able to generate energy, they absorb heat from the sun hence why they cope better in warmer climates. Butterflies are important to the environment as they pollinate plants, the nectar providing them with energy. Method: For the past 41 years, Hengistbury Head have conducted a weekly butterfly transect walks during the breeding season. This transect consists of pathways dissecting various habitats. Data is recorded between the weeks of 1st April and 30th September due to the butterflies being more frequent during warmer temperatures; they tend to go into hiding and try to find shelter to keep warm in cooler conditions. There are 14 sections in the transect at Hengistbury Head, which can be seen in figure 1, each comprising a variety of plants and conditions. For example, section 1, takes place on the cliff on the coast and is an open environment where butterflies can easily be spotted. In contrast to this, section 7 is based at the Lily Pond at the top of the Head, is surrounded by trees, making it a more ‘closed-in’ environment. Section 14, however, is quite a mixed environment; there are large bushes and trees that butterflies are able to hide in but can also roam freely across the broad pathway. Figure 1, Map of the Hengistbury Head butterfly transect. 1 When walking the transect, the ideal weather would be sunny with very little wind. The temperature, windspeed, wind direction and percentage of sun was recorded each time the transect was walked. This may provide an indication as to why there were more, or fewer numbers of butterflies on that transect on that occasion. Results: The number of butterflies seen every year, as well as what species are present, are affected by several variables. One of these is a change in the weather and migration, due to global climate changes. Figure 2 shows the abundance of butterflies in 2019. Summary Table of Butterflies Spotted on the Transect Route 2019 347 350 300 250 200 162 125 150 95 108 100 68 60 26 26 33 50 15 15 2 2 3 1 10 23 7 2 7 10 0 2019 IN NUMBER BUTTERFLIES OF SPECIES OF BUTTERFLY Figure 2, Summary table of the number of butterflies spotted on the transect route in 2019. The most abundant species of butterfly in 2019 was Pyronia tithonus, who’s common name is Gatekeeper. Although its appearance has fluctuated significantly since it was first recorded in 1979, when compared to the results from 2018, shown in figure 3, the Gatekeeper, was still consistently frequent on the reserve. The Meadow Brown (Maniola jurtina) is the second most common species found at Hengistbury Head. Although it has fluctuated in numbers, similar to the Gatekeeper, since 1979, it has decreased slightly over recent years; the most common sighting of the Meadow Brown occurred in 1983 with over 600 appearances. The Small White (Pieris rapae) was the third most common butterfly recorded here in 2019. In previous years, the pattern seems to be that there are an increasing number of sightings of the Small White over a period of a couple of years, following this there is a drop in the number of sightings, then the pattern returns to an increase. For example, 2 the abundance of the Small White was highest in 2013 with over 250 sightings. In the upcoming years, the number rapidly declined until 2017 where the trend started to increase again. The abundance of the three most common species of butterfly over the last five years 700 661 600 500 400 348 347 329 300 224 222 180 200 167 166 162 125 100 73 54 33 42 0 Gatekeeper Meadow Brown Small White 2015 2016 2017 2018 2019 Figure 3, Comparison of the abundance of the three most common species of butterfly in 2019, over the last five years. Comparison of the species of butterfly present in 2018 and 2019 Ringlet 107 Small Heath 108 106 Meadow Brown 162 343 Gatekeeper/Hedge Brown 347 Speckled Wood 33 95 Comma 718 Peacock 26 17 Small Tortoiseshell 28 Painted Lady 60 4 Red Admiral 26 15 Holly Blue 71 Common Blue 23 54 Small Copper 1013 Purple Hairstreak 1 Green Hairstreak 31 Orange Tip 10 SPECIES OF BUTTERFLY Green-Veined White 5 Small White 125 54 Large White 95 48 Brimstone 2 Clouded Yellow 2 Large Skipper 1516 Essex Skipper 155 Small Skipper 68 107 0 50 100 150 200 250 300 350 2019 2018 Figure 4, Comparison of the species of butterfly present in 2018 and 2019. 3 Additionally, when compared to the results from 2018, there appears to be an increased number of butterflies overall, as well as the appearance of more species. For example, in figure 4, the number of butterflies recorded in 2018 was 1094. However, in 2019 there were 1147 butterflies, indicating that the population of butterflies overall at Hengistbury Head had increased. A possible reason for this increase is an increase in other butterfly species, shown in figure 5, such as the appearance of the Colias croceus, also known as the Clouded Yellow. The number of Clouded Yellows is not significantly high, with only two of them appearing on the transect in September. However, in previous years the number of Clouded Yellows present have been higher, with the highest being 40 in the year 2000. Nonetheless, that does not mean that the number of Clouded Yellows has not contributed to the increase in recordings in 2019. The abundance of the three species of butterfly spotted in 2019 compared to the last 5 years 9 8 8 8 7 7 6 5 4 3 2 2 2 2 1 1 0 0 0 0 0 0 0 0 0 Clouded Yellow Brimstone Purple Hairstreak 2015 2016 2017 2018 2019 Figure 5, Comparison of the abundance of the three species of butterfly spotted in 2019 compared to the last five years. Two species of butterfly that were not seen on the transect in 2019 were the Orange Tip (Anthocharis cardamines) and the Green-Veined White (Pieris napi). Interestingly in 2018, the Orange Tip recorded its highest number of sightings, so it is a concern than none were spotted this year. The Green-Veined White has been more common over the years, with it being present almost every year since 2002. The abundance of this species fluctuates every year, with the most being seen in 1981. After 1981, it is only present every other year and mainly in high quantities. However, after 2002, the butterfly has been spotted almost every year but only in small quantities. Therefore, it is not uncommon for there to be a year where the Green-Veined White is not recorded. Although the two species may not have been present in 2019, they were both seen and recorded in 2018; the comparison between the two years can be seen in figure 4. Figure 4 shows the number of Green- Veined White butterflies recorded which came to a total of 5, as well as the Orange Tip coming to a total of 10 in 2018. Discussion: Hengistbury Head is a Site of Special Scientific Interest (SSSI), a designation aimed at protecting the land and the wildlife inhabiting it. The protection of butterflies is vital in conserving the environment with one of the reasons is that they pollinate our food sources - alongside other pollinators (Harris, 4 2018). Additionally, there a reducing number of open spaces that allow for shelter and breeding due to habitat loss, development and succession. It does not go unnoticed that the majority of butterflies have been declining since 1979. The population changes of butterflies in the UK is likely largely affected by the weather changes resulting from climate change; many populations of species have fluctuated significantly over the years. The temperature has increased so much so that the top 10 hottest years have all occurred since 2002. The hottest year since 1880 was 2014, with global temperatures increasing 0.69oC above the 20th century average of 13.9oC (NOAA National Centers for Environmental Information). Although butterflies are ‘poikilotherms’ and need warmth to be able to generate energy, such extreme weather conditions have also been known to negatively affect them. In a study carried out by Long, et al (2016), univoltine (single-brood) and multivoltine (multi-brood) butterflies were placed in various extreme climatic conditions to see how they would react to each environment, whether it would be a negative effect or a positive effect. This was tested at all life stages of the species. It was found that at all life stages of univoltine species, the extreme climates affected their thermo- sensitivity; the extreme heat became harmful to them in contrast to the extreme cold, which benefited them.