Butterfly Monitoring at North Dam Meadows, Hanningfield.
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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 2003. 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.
3. Monitoring Results.
3.1. Species Abundance
250
200
Average Abundance
150
100
50
0
2003 2004 2005 2006 2007 2008 2009
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 2009.
90
80
70
Average Abundance
60
50
40
30
20
10
0
2003 2004 2005 2006 2007 2008 2009
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.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 2009. 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 2007. 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 2009. 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 2009.
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.
3.2. Month of First Appearance.
Meadow Brown
April May June July August September October
2003 0 0 871 2624 246 4 0
2004 0 0 336 3230 107 6 0
2005 0 0 600 2454 120 7 0
2006 0 0 560 2115 322 0 0
2007 0 0 726 1560 60 12 0
2008 0 0 285 1327 245 N/A N/A
2009 0 0 605 985 143 0 N/A
Fig 2a Monthly abundance of the meadow brown (Maniola jurtina). N/A indicates no
record.Gatekeeper
April May June July August September October
2003 0 0 0 1970 287 0 0
2004 0 0 0 1971 2 1 0
2005 0 0 0 1736 215 0 0
2006 0 0 0 850 420 0 0
2007 0 0 0 386 117 1 0
2008 0 0 0 704 454 N/A N/A
2009 0 0 1 653 409 0 N/A
Fig 2b Monthly abundance of the gatekeeper (Pyronia tithonus). N/A indicates no
record.
Ringlet
April May June July August September October
2003 0 0 28 202 0 0 0
2004 0 0 8 269 0 0 0
2005 0 0 27 331 2 0 0
2006 0 0 43 524 0 0 0
2007 0 0 32 455 0 0 0
2008 0 0 235 618 1 N/A N/A
2009 0 0 623 959 1 0 N/A
Fig 2c Monthly abundance of the ringlet (Aphantopus hyperantus). N/A indicates no
record.
Clouded Yellow
April May June July August September October
2003 0 0 0 1 9 99 28
2004 0 0 0 0 2 2 4
2005 0 0 0 1 0 0 0
2006 0 0 0 1 4 1 15
2007 0 0 0 0 7 20 1
2008 0 0 0 0 0 N/A N/A
2009 0 0 0 0 1 1 N/A
Fig 2d Monthly abundance for the clouded yellow (Colias croceus). N/A indicates no
record.Large White
April May June July August September October
2003 0 7 1 39 17 46 1
2004 0 24 13 154 14 37 4
2005 4 31 17 171 18 15 4
2006 0 9 13 56 38 44 0
2007 3 2 16 34 9 24 1
2008 1 17 14 75 29 N/A N/A
2009 4 24 22 206 55 13 N/A
Fig 2e Monthly abundance for the large white (Pieris brassicae). N/A indicates no
record.
Small White
April May June July August September October
2003 2 3 16 68 136 215 2
2004 4 43 16 437 190 170 6
2005 2 32 21 312 34 45 2
2006 2 10 11 88 107 80 3
2007 13 12 17 74 101 104 1
2008 0 20 25 284 45 N/A N/A
2009 6 20 57 327 168 65 N/A
Fig 2f Monthly abundance for the small white (Pieris rapae). N/A indicates no
record.
Green-veined White
April May June July August September October
2003 2 2 8 56 16 18 1
2004 1 18 3 51 8 5 0
2005 6 16 7 58 3 4 0
2006 0 5 3 44 22 8 0
2007 5 7 25 69 19 9 0
2008 0 10 3 27 10 N/A N/A
2009 3 6 3 52 16 3 N/A
Fig 2g Monthly abundance for the green-veined white (Pieris napi). N/A indicates no
record.Common Blue
April May June July August September October
2003 0 183 700 88 747 360 17
2004 0 231 861 49 245 156 2
2005 0 8 404 31 80 107 2
2006 0 11 73 148 410 64 11
2007 0 0 133 4 51 28 0
2008 0 31 108 21 37 N/A N/A
2009 0 23 63 15 161 11 N/A
Fig 2h Monthly abundance for the common blue (Polyommatus icarus). N/A
indicates no record.
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 30th 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.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 2003. 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 green- veined 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: http://www.butterfly-conservation.org/Butterfly/32/Butterfly.html?ButterflyId=5 [Date accessed 8th February 2009]. Centre for Ecology and Hydrology (2006). Species list (grouped by taxonomic family) Available from: http://www.ceh.ac.uk/news/news_archive/2009_news_item_14.html [Date accessed: 21st December 2009] UK Butterfly Monitoring Scheme (2009) UK butterfly numbers fall to an all time low - 8 April 2009. Available from: http://www.ukbms.org/speciesLists/species_by_family.htm [Date accessed: 21st 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 2008. CEH: Wallingford.
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