Butterfly Monitoring at North Dam Meadows, Hanningfield.

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1 Butterfly Monitoring at North Dam Meadows, Hanningfield. 1. Introduction Butterflies act as environmental indicators, being sensitive to changes in climate and habitat. Having short life cycles and high rates of reproduction enable these organisms to respond rapidly to environmental change, with trends in their populations reflecting the responses of other wildlife. The UK Butterfly Monitoring Scheme has reported butterfly numbers in summer 2008 to be the lowest recorded since the monitoring programme began, showing an accelerated decline from previous years. Wet summers resulting from climate change have been linked to the fall in populations of both common and rarer butterfly species; the orange tip (Anthocharis cardamines) and the small tortoiseshell (Aglais urticae) have undergone rapid decline over the last decade, with the latter once being the most common garden butterfly in Britain. Phenology, the term used to define seasonal activities of organisms, can also be used as an indicator of climate change. Recent studies on butterfly phenology have found correlations between the timing of first annual appearance and atmospheric temperature. Warmer temperatures have led to many butterfly species being observed earlier in the year than previously recorded, a phenomenon thought to be caused by global warming. 2. Site Management and Monitoring History The calcareous grasslands of North Dam Meadows are located to the North of Hanningfield Reservoir and are cut annually for conservation. Cuttings are removed to prevent smothering the grassland flora and enriching the soil and consequently, the site has become a haven for butterflies. Local butterfly enthusiasts Jim Smith and Roy Widgery have been monitoring the butterflies of North Dam Meadows for nearly ten years and collecting data for Essex and Suffolk Water since Monitoring is conducted via a set transect walk where all butterfly species seen from the transect are recorded. Although this methodology is indicative of butterfly abundance, total numbers present at the site may be considerably higher. 26 species have been observed at North Dam Meadows since 2003, including the small heath, a UK BAP priority species. Of the 26 butterfly species monitored, the data for eight were selected for analysis, including the meadow brown (Maniola jurtina), the gatekeeper (Pyronia tithonus), the ringlet (Aphantopus hyperantus), the large white (Pieris brassicae), the small white (Pieris rapae), the green-veined white (Pieris napi) and the common blue (Polyommatus icarus). All are common within Britain and are reflective of habitat quality, which is correlated indirectly with suitability of land management. The clouded yellow (Colias croceus) was also selected. The species occurs in Britain in the spring, having migrated from Southern Europe and North Africa and is therefore a good indicator of climate change.

2 Average Abundance Average Abundance 3. Monitoring Results Species Abundance Year Meadow Brown Gatekeeper Ringlet Fig 1a Yearly total abundance averaged by sample size for the meadow brown, the gatekeeper and the ringlet from 2003 to Year Clouded Yellow Large White Small White Green-veined White Common Blue Fig 1b Yearly total abundance averaged by sample size for the clouded yellow, the large white, the small white, the green-veined white and the common blue from 2003 to 2009.

3 Figures 1a and 1b clearly show the change in abundance of the eight species selected over the six year sampling period. Both the meadow brown and the gatekeeper have undergone a decline in numbers (Figure 1a). Average total abundance of the meadow brown has fallen since 2004, from 194 to 96 in Similarly, the numbers of the gatekeeper have also decreased since the survey began. An average abundance of 107 was recorded in 2003, which fell to 24 in Since then, the species appears to be recovering steadily, increasing to average numbers of 64 and 59 in 2008 and 2009 respectively. Figure 1b also demonstrates an overall decline in numbers of the common blue. Average abundance dropped by 58 between 2004 and 2005, falling to the lowest numbers ever recorded in 2007, when a mean of just ten individuals was observed. In the last two years of monitoring, numbers of the common blue have remained low. In contrast to the meadow brown and the gatekeeper, the ringlet has shown an overall increase in average yearly abundance over time (Figure 1a) Average numbers have increased sevenfold, from a mean of 11 individuals in 2003, to 88 in The last two years of the survey have seen a more dramatic increase in numbers, with observations doubling from the previous yearly average in both 2008 and Trends in average yearly abundance have been similar in two species of white surveyed. Both the small and the large white increased in numbers after the first year of monitoring, only to decrease in 2005 (Figure 1b). From 2007, populations of these two butterfly species have risen, mimicking the increase in numbers of the ringlet. Numbers recorded in 2009 have exceeded the values recorded in the first year of monitoring for both the large and small white. Observations of the clouded yellow and the green-veined white have remained low in all years (Figure 1b, Figure 2d and Figure 2g), hence clear changes populations are difficult to determine. Average yearly abundance of the clouded yellow was highest in 2003 at seven and remained at one or below in following years. Throughout the survey period, recordings of the green-veined white have fluctuated between an average of seven and three. When in flight, the green-veined white has an affinity with the small white. Only specimens confirmed as the former species were therefore included in the monitoring records, giving low numbers in consecutive years Month of First Appearance. Meadow Brown N/A N/A N/A Fig 2a Monthly abundance of the meadow brown (Maniola jurtina). N/A indicates no

4 Gatekeeper N/A N/A N/A Fig 2b Monthly abundance of the gatekeeper (Pyronia tithonus). N/A indicates no Ringlet N/A N/A N/A Fig 2c Monthly abundance of the ringlet (Aphantopus hyperantus). N/A indicates no Clouded Yellow N/A N/A N/A Fig 2d Monthly abundance for the clouded yellow (Colias croceus). N/A indicates no

5 Large White N/A N/A N/A Fig 2e Monthly abundance for the large white (Pieris brassicae). N/A indicates no Small White N/A N/A N/A Fig 2f Monthly abundance for the small white (Pieris rapae). N/A indicates no Green-veined White N/A N/A N/A Fig 2g Monthly abundance for the green-veined white (Pieris napi). N/A indicates no

6 Common Blue N/A N/A N/A Fig 2h Monthly abundance for the common blue (Polyommatus icarus). N/A indicates no Through the comparison of Figures 2a to 2g, it is evident that the month of first appearance varies between species. Appearing earlier than any of the other species analysed were the large white, the small white and the green-veined white, which were first seen in April of every year (Figures 2e, 2f and 2g). In May, the common blue appears at North Dam Meadows (Figure 2h). The first month of appearance of the ringlet and the meadow brown was later in the year; A. hyperantus and M. jurtina were first observed in June for every year of the monitoring programme (Figures 2a and 2c). With the exception of 2009, the gatekeeper was first recorded in July (Figure 2b). The date of the observation in 2009 was 30 th June, hence, the species was not seen significantly earlier than in this year than in previous years. Over the duration of the monitoring period, numbers of the clouded yellow were low, making it difficult to determine a month of first appearance. Single specimens were seen in July in 2003, 2005 and 2006 (Figure 2d). Due to the low numbers of observations, identifying July as the month of first appearance would be an unreliable conclusion. August was the month of first appearance in 2004, 2009 and 2007 and in 2008, C. croceus was absent from North Dam Meadows (Figure 2d). Discussion Variation in timing of first appearance is known to differ between butterfly species. Commencing in 1976, detailed monitoring by the UK Butterfly Monitoring Scheme has identified average dates of first appearance for many species of butterfly. Such rigorous surveying coupled with the collection of meteorological data has enabled correlations to be made between changes to the average date of first appearance and climate change. The variation in trends for the average yearly abundance between species at North Dam Meadows could be due to changing climate, alterations to the habitat management regime and associated habitat quality, or a combination of the two variables. Other localised factors, such as disease and reproductive success could also be accountable. To contextualise the changes in average yearly butterfly abundance for North Dam Meadows in future years, meteorological data will be collected and habitat quality parameters measured, in addition to alterations to the management regime being recorded. This will promote an understanding of the significance of the role of such variables in governing fluctuations in populations.

7 Conclusions Whilst numbers of some butterfly species have risen over the six year monitoring period, others have fallen dramatically. Populations of the meadow brown and the gatekeeper have decreased substantially in six years. The opposite is true for the ringlet, which has increased sevenfold since Numbers of the small and large white have recovered in recent years to exceed numbers recorded in the first year of monitoring. Populations of the green-veined white and the clouded yellow remain low. The month of first appearance is also species-specific. The large, small and greenveined whites first appear in April, followed by the common blue in May. The meadow brown and ringlet appear later in June. In July, the gatekeeper is first seen. The month of first appearance of the migrant species the clouded yellow remains inconclusive due to low numbers. Essex and Suffolk Water would like to thank Roy Widgery and Jim Smith for their dedication and hard work, without which this insight into the butterflies of North Dam Meadows would not have been possible. Their data will provide a vital indicator on which to tailor the future management of the grasslands and clues to the effect of climate change on North Dam Meadows butterflies. References Butterfly Conservation (No date). A-Z of butterflies Clouded Yellow. Available from: [Date accessed 8 th February 2009]. Centre for Ecology and Hydrology (2006). Species list (grouped by taxonomic family) Available from: [Date accessed: 21 st December 2009] UK Butterfly Monitoring Scheme (2009) UK butterfly numbers fall to an all time low - 8 April Available from: [Date accessed: 21 st December 2009]. Botham, M.S., Brereton, T.M., Middlebrook, I., Cruickshanks, K.L., Harrower, C., Beckmann, B., & Roy, D.B (2008). United Kingdom Butterfly Monitoring Scheme report for CEH: Wallingford.