BUTTERFLIES AT HENSTEAD 1997–2002
21
CHANGES IN THE NUMBER OF BUTTERFLIES VISITING A GARDEN IN NORTH-EAST SUFFOLK, 1992–2007 PETER J. DARE Introduction The Suffolk butterfly fauna, past and present, has been well documented in recent years by means of distribution atlases (Mendel & Piotrowski, 1986; Stewart, 2001) and transect counts in breeding habitats while Stewart (1994, 1995) published the results from a county-wide garden survey. The annual surveys of garden butterflies and their preferred nectar plants organized by Butterfly Conservation reflect the rapidly growing interest in the hobby of ‘butterfly gardening’. Indeed, gardens now afford an increasingly important habitat for many butterflies, especially in counties such as Suffolk where so much natural habitat has been destroyed by agricultural and other developments (Stewart, 2001). A Suffolk survey in 1994 documented the relative frequency with which 31 species visited a sample of 152 gardens, as well as listing those plants observed to be most important either as nectar sources or for breeding (Stewart, 1995). For 16 years from 1992 I systematically counted the numbers of butterflies visiting our small rural garden in north-east Suffolk at Henstead (TM496859) located 4 km from the North Sea coast. This article summarises results from a simple, but semi-quantitative, recording scheme. It shows how this could be used more widely to measure how our garden butterfly populations change both seasonally and, perhaps more importantly for conservation, how they fluctuate in abundance between years. Garden Features The 0·3 acre garden is very sunny but rather exposed to easterly winds. Arable land adjoins the east side whereas hedges, scattered trees and neighbouring gardens afford reasonable protection from other winds. Several deciduous spinneys are within 0·5–1 km and two extensive deciduous woodlands within 5 km. Nearby to the north there are water meadows along the narrow Hundred River. The garden comprised lawns (with weeds), flower beds, two small shrubberies plus scattered bushes of lilac, rose, elder, Ribes, dogwood and broom. There were several tall trees – a massive snow gum (Eucalyptus sp.) and young sycamores (2), oaks (2), ash (1) and a large wild pear. Also providing shelter for butterflies were a low hedge of Spiraea, hawthorn and other bushy growth along the exposed field edge; a long tall hedge of thickly ivy-covered young (partly diseased) elms; a long ivy-covered wooden fence; and small ‘wild’ patches of nettles, rough grasses and mixed crucifers, umbellifers and so on. Over the first 5–10 years, we increased the variety of nectar sources to span the butterfly season. In particular, buddleias were allowed to spread, and we planted or encouraged Hebe shrubs (2), Escallonia, asters, ice-plants (Sedum), Aubretia, Salvia, thyme, oregano, lavender, catmint, honesty, Verbena bonariensis and other attractant flowers. Brambles and rough grassy verges occurred on the bank at the gate and along the lane. All the above flowers attracted butterflies except for the lavender.
Trans. Suffolk Nat. Soc. 44 (2008)
22
Suffolk Natural History, Vol. 44
Methods Throughout this study I used a recording form designed by the Essex Wildlife Trust. After a trial run in 1991, I extended its ‘year’ to 40 weeks by adding October and November. The standard starting date each year was chosen as 1 March, irrespective of the day of week on which it occurred. Daily observations were made, weather and other commitments permitting, until the end of the season. On suitable days, one or more ‘spot-counts’ of each species were made at different times, the number and timing of garden inspections varying mainly with the ambient conditions. In general, butterflies were found to be most active and diverse between 09.00–15.00 h BST. For every 7-day period I scored on the form the highest spot-count of each species during that week. At the end of the year, each species’ weekly scores could be plotted as a phenological bar chart to show its changing seasonal pattern of occurrence. This procedure provides sufficient data from a very small site to describe ‘average’ seasonal patterns, as it smoothes out inevitable short-term variability in numbers and timing (phenology) due to erratic weather fluctuations, both within and between years. Yearly variations in total abundance of any species were examined by summing all the 7-day peak counts through a given year, to provide an annual score or index of abundance. These can be compared with meteorological data to investigate whether particularly ‘good’ or ‘bad’ years might be linked to unusual local weather conditions or other environmental variables. More importantly, plotting the 16 years of annual indices also gives the possibility of detecting any trends and cycles in butterfly numbers. This was examined by fitting linear or polynomial trend lines to the plotted annual data. The relative abundance or ranking of each butterfly in the overall population diversity was measured by adding all of its 16 annual scores to give an overall species index. Observations Species Diversity and Relative Abundance A total of 28 species was recorded during the 16 years. The 19 commonest butterflies are ranked by their aggregated scores in Table 1. Also given for each species is the highest number of individuals present at any one time. The four most numerous butterflies were Small Tortoiseshell, Large White, Peacock and Red Admiral which made up 63% of the population index. They, and the Painted Lady, were all heavily dependent upon the buddleias, which were pruned sequentially in spring so as to prolong their flowering into late September or early October. The high ranking of migrant Painted Lady reflected big influxes in 1996 and 2003 (see later). The nine scarcest species (not listed in Table 1) were: Brimstone (6 visits), Green Hairstreak and Brown Argus (5 each), White-letter Hairstreak (3), Grayling and White Admiral (2 each), with single occurrences of Essex Skipper, Clouded Yellow and Queen of Spain Fritillary (the last, in September 1997, probably being from the 1996–1998 Minsmere ‘colony’).
Trans. Suffolk Nat. Soc. 44 (2008)
BUTTERFLIES AT HENSTEAD 1997–2002
Species
23
Table 1. Relative abundances of butterflies 1992–2007 % of total annual Total indices of Latin name Score all species
Small Tortoiseshell Peacock Large White Red Admiral Small White Gatekeeper Comma Green-veined White Meadow Brown Painted Lady Holly Blue Orange Tip Speckled Wood Small Copper Wall Brown Common Blue Ringlet Small Skipper Large Skipper
Aglais urticae Inachis io Pieris brassicae Vanessa atalanta Pieris rapae Pyronia tithonus Polygonia c-album Pieris napi Maniola jurtina Cynthia cardui Celastrina argiolus Anthocaris cardimines Pararge aegeria Lycaena phlaeas Lasiommata megera Polyommatus icarus Aphantopus hyperantus Thymelicus sylvestris Ochlodes venata
1,544 1,064 981 871 486 353 311 282 267 254 227 94 68 61 54 42 39 33 28
22 15 14 12 7 5 4 4 4 4 3 <1 <1 <1 <1 <1 <1 <1 <1
Max. Count 58 41 80 22 14 13 9 4 6 27 6 2 3 1 1 4 2 2 2
Annual Fluctuations and Longer-term Trends in Abundance of each Species Fluctuations and trends in butterfly numbers over the 16 years are shown (Figs. 1–5) by the annual indices, to many of which have been fitted statistically either linear or polynomial trend lines. The total butterfly population showed no significant (p = 0.24) overall trend in numbers (Fig. 1) until a downturn over the last three years. The overall index varied by a factor of around 2·5 between the two poorest years (1992, 2005) and the best years (1997, 2003). There was a gradual increase in the number of species observed each year, from 13 in 1992 to 18 in 1995, and to 22 in 1999 and 2004, before falling back to 16–18 in the last few years. Surprisingly, the highest diversity was noted in two of the years that were not especially good for total numbers. Table 2 summarises the years of highest and lowest numbers for each of the 12 most numerous butterflies, and for all species combined. There is little or no indication of any synchronicity between two or more species except in the very poor year 1992. Instead, the extreme high and low years for each species appear to have occurred independently of the others. Nevertheless, within individual families some interesting patterns and contrasts are discernible.
Trans. Suffolk Nat. Soc. 44 (2008)
Trans. Suffolk Nat. Soc. 44 (2008)
1
6
1
4
6
2
1 1
2
L
1
3
L
H
H
H
2
1
L
L
H
1
H
L
2
2
H
L
H
0verall best and worst (joint worst) years are indicated with bold font
Total Species High Total Species Low
L L
L
H
1996
L
L
L
L H
1999
L
L
2000
L L
H
1
2
H
H
L
2001
L
L
1
1
L
H
2002
Red Admiral Painted Lady Small Tortoiseshell Peacock Comma Gatekeeper Meadow Brown
H
L
1992
L
H
1
2
H
H
L
H
1
3
L H H
H
2004
Holly Blue
1993
L
1994 H
L
1997
L
1998
L
1995 L
2003
L
1
4
H
L
H
H
L H
2005
L
1
L
L
2006
H L
3
1
L
L
H
L L
2007
Total Butterflies Large White Small White Green-veined White Orange Tip
Table 2. years of highest and lowest numbers for each of the 12 most numerous butterflies, 1992â&#x20AC;&#x201C;2007
24 Suffolk Natural History, Vol. 44
BUTTERFLIES AT HENSTEAD 1997–2002
25
800
1. Total butterfly abundance
700
annual combined indices
600 500 400 300 200 100
y = -8.4471x + 17315 R² = 0.1043
0 1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
Figure 1. Annual variations in total butterfly abundance, 1992–2007 350
2a. Small Tortoiseshell
300
annual indices
250 200 150 100 50 0 1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
140
2b. Peacock
120
annual indices
100 80 60 y = -0.4414x2 + 1762.8x - 2E+06 R² = 0.3234
40 20 0 1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
Figure 2. Annual variations in abundance of the five vanessid species
Trans. Suffolk Nat. Soc. 44 (2008)
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26 100
2c. Red Admiral
90 80
annual indices
70 60 50 40 30 20 10 0 1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
50
2d. Comma
45 40 35
annual indices
30 25 20 15 y = -0.1879x2 + 753.26x - 755084 R² = 0.6441
10 5 0 1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
90 80
2e. Painted Lady
annual indices
70 60 50 40 30 20 10 0 1990
1992
1994
1996
1998
2000
2002
2004
2006
Figure 2. Annual variations in abundance of the five vanessid species
Trans. Suffolk Nat. Soc. 44 (2008)
2008
BUTTERFLIES AT HENSTEAD 1997–2002
27
Thus, of the three commonest vanessid butterflies (Figs. 2a–e), annual variability in numbers was high, ranging from a factor of 24 in resident Small Tortoiseshell to 6 in Peacock and 9 for migrant Red Admiral. There was a significant increase in Comma numbers (p = 0.001) but an erratic and nearly significant (p = 0.059) decline in Small Tortoiseshells to recent very low numbers. There has been a steady decline in the Peacock index since 2003 whereas Red Admiral numbers have been more or less stable since 1994. The migrant and irruptive Painted Lady was scarce or absent in all years except 1996, 2003 and 2006 which were notable immigration years nationally. Among the whites (Pieridae, Figs. 3a–d), the resident Green-veined White increased rapidly to a peak around 1999 but then stabilized at a slightly lower level; whereas the Small White increased significantly (p = 0.023), though with marked annual variations, from a run of poor years in the early 1990s. The partially migrant Large White showed no trend over the 12 years since its major irruption year in 1992. Orange Tips appear to have been more or less stable though never numerous. 35
3a. Green-veined White
30
annual indices
25 20 15 10 5 0 1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
70
3b. Small White
60
annual indices
50 40 30 20 y = 1.9515x - 3871.3 R² = 0.2973
10 0 1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
Figure 3. Annual variations in abundance of the four Pieridae species
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28 250
3c. Large White annual indices
200
150
100
50
0 1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2004
2006
2008
11
3d. Orange Tip
10
annual indices
9 8 7 6 5 y = 0.0205x2 - 81.767x + 81606 R² = 0.1831
4 3 2 1990
1992
1994
1996
1998
2000
2002
Figure 3. Annual variations in abundance of the four Pieridae species In the browns (Satyridae, Figs. 4aâ&#x20AC;&#x201C;e), the Gatekeeper increased steadily to a peak in 2003 before declining, while a similar but earlier rise in the Meadow Brown index was also reversed. The Meadow Brown trend was not significant 50
4a. Gatekeeper
45
annual indices
40 35 30 25 20 15 10 5 1990
1992
1994
1996
1998
2000
2002
2004
2006
Figure 4. Annual variations in abundance of the five Satyridae species
Trans. Suffolk Nat. Soc. 44 (2008)
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BUTTERFLIES AT HENSTEAD 1997â&#x20AC;&#x201C;2002
29
(p = 0.148).Visits from both Ringlet and Speckled Wood became increasingly frequent since they first appeared here in 1997 and 1999 respectively. In contrast, Wall Browns became rapidly scarcer after 1998 with none being seen in the last three years; a highly significant trend (p = 0.005). 40
4b. Meadow Brown
35
annual indices
30 25 20 15 y = -0.1579x2 + 631.74x - 631816 R² = 0.255
10 5 1990 16
14
1992
1994
1996
1998
2000
2002
2004
2006
2008
1998
2000
2002
2004
2006
2008
2000
2002
2004
2006
2008
4c. Speckled Wood
annual indices
12 10 8 6 4 2 0 1990
1992
1994
1996
8 7
4d. Ringlet
annual indices
6 5 4 3 2 1 0 1990
1992
1994
1996
1998
Figure 4. Annual variations in abundance of the five Satyridae species
Trans. Suffolk Nat. Soc. 44 (2008)
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30 9
4e. Wall Brown
8
annual indices
7 6
y = -0.0354x2 + 141.01x - 140564 R² = 0.5624
5 4 3 2 1 0 1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
Figure 4. Annual variations in abundance of the five Satyridae species 40
5a. Holly Blue
35
annual indices
30 25 20 15 10 y = 0.7103x - 1406.3 R² = 0.1242
5 0 1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
12
5b. Small Copper
annual indices
10
8 y = -0.1426x + 289.16 R² = 0.0414 6
4
2
0 1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
Figure 5. Annual variations in abundance of the three Lycaenidae species
Trans. Suffolk Nat. Soc. 44 (2008)
BUTTERFLIES AT HENSTEAD 1997–2002
31
18
5c. Common Blue
16
annual indices
14 12 10 8 6 4 2 0 1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
Figure 5. Annual variations in abundance of the three Lycaenidae species Of the blues (Lycaenidae, Figs. 5a–c), the resident Holly Blue increased, though not significantly (p = 0.181), whilst also displaying its well-known cyclical fluctuations in numbers. The Small Copper, always uncommon here, became scarcer after 1999 though not significantly so (p = 0.450). The Common Blue was an irregular visitor up to 2001 but then disappeared. Its nearest (small) breeding colony is 4 km away near the coast. The various trends for these 17 species can be summarised as follows: Increase (long term) Increase (recent arrival) Increase, then ‘stable’ No long term trend (‘stable’) Decrease, recent (after earlier increase) Decrease (long term, major)
2 2 3 3 5
Small White, Holly Blue Speckled Wood, Ringlet Comma, Red Admiral, Green-veined White Painted Lady, Large White, Orange Tip Peacock, Meadow Brown, Gatekeeper, Small Copper, Common Blue 2 Small Tortoiseshell, Wall Brown
In summary, 7 of these 17 commonest species became less numerous during the last 5–10 years, 4 increased and 6 were either stable or showed no long-term trend. All these species (except Painted Lady) breed annually in Suffolk, though four are either total (Painted Lady, Red Admiral) or partial (Large and Small White) migrants from the Continent.
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Diversity and Seasonal Abundance Butterflies were observed in all months except January. The earliest butterfly was a Small Tortoiseshell on 14 February (1998) and the latest was on 9 December 2000, when a Red Admiral was sunning itself below a sheltering hedge (shade temperature 10oC). The combined seasonal abundance pattern for all butterflies (Fig. 6) is derived by plotting the aggregated scores for each week through each year. Butterfly numbers were very low throughout spring and early summer before increasing dramatically from mid-July to become most numerous from late July through August. The summer index was about 12 times higher than the spring index. Early September numbers were also high, matching those of mid-July, before a steep decline set in. The earliest and latest dates of sightings for the 19 regular species are listed in Table 3. All were within the range of extreme dates recorded for Suffolk (Stewart, 2001). Spring appearances were markedly later than expected, given the recent long sequence of mild winters, whereas last autumn sightings were more in accord with the county dates. For the six most regular spring species, their first appearance dates varied greatly between years (Table 4). Thus, the earliest dates when Small Tortoiseshells and Peacocks reappeared after hibernation differed by about two months, as did dates for Holly Blue which over-winters in the pupal stage. 900 800 700
Cumulative index
600 500 400 300 200 100 0
Dec. 6
Nov. 22
Nov. 8
Oct, 25
Sep. 27
Trans. Suffolk Nat. Soc. 44 (2008)
Oct. 11
Sep. 13
Aug. 30
Aug. 16
Aug. 2
Jul. 19
Jul. 5
Jun. 21
Jun. 7
May. 24
Apr. 26
May. 10
Mar. 29
Apr. 12
Mar. 15
Mar. 1
Feb. 1
Feb. 15
Week
Figure 6. All Species: total seasonal abundance, 1992-2007
BUTTERFLIES AT HENSTEAD 1997–2002
33
Table 3. Earliest and latest dates for butterflies in the garden, 1992–2007 Species
Earliest
Latest
Small Tortoiseshell Peacock Comma Green-veined White Holly Blue Speckled Wood Orange Tip Small White Large White Small Copper Painted Lady Red Admiral Wall
February 14 March 13 March 23 April 1 April 1 April 13 April 14 March 12 April 29 May 3 May 6 May 8 May 13
November 25 November 1 November 11 October 15 September 22 September 27 June 20 October 19* October 30** October 20 October 20 December 9 October 20**
Common Blue Meadow Brown Large Skipper Ringlet Small Skipper Gatekeeper
May 25 June 10 June 18 June 19 June 29 July 8
September 22 September 8 August 4 August 2 August 25 September 4
*date within 8 days of county latest, **date within 12 days of county latest (R. Parker, in litt.)
(Spring Commas were too scarce for analysis). In contrast, annual variations in Orange Tip and Green-veined White first appearances (from pupae) were only about 1 month). Plots of these dates (Fig. 7) indicate no statistically significant trends in the timing of first appearance over this 16-year time series; a tendency towards a progressively earlier appearance is suggested only for Small White but that was due largely to the exceptionally early individual in 2007. Table 4. First appearance dates of spring butterflies in the garden, 1992–2007
Small Tortoiseshell Peacock Holly Blue Green-veined White Small White Orange Tip
Mean date
Earliest
Latest
Mar 29 Apr 19 Apr 22 Apr 21 Apr 28 Apr 29
Feb 14 (1998) Mar 13 (1997) Apr 1 (1996) Apr 2 (1995) Mar 12 (2007) Apr 14 (1995)
Apr 21 (1996) May 14 (2006) May 31 (2000) May 8 (2001) May 16 (1994) May 13 (1994)
Range (days) 66 62 60 36 65 29
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7a. Small Tortoiseshell
60
7d. Small White days after March 1st
days after March 1st
50 40 30 20
y = 0.1181x - 206.45 R² = 0.001
10 0
-10 -20
1990
1994
1998
2002
90 80 70 60 50 40 30 20 10 0
y = -1.9892x + 4035.3 R² = 0.3003
1990
2006
2002
2006
80
70 d ays after March 1st
dates after March 1st
70
60 50 40 30 20
y = -0.1735x + 381.72 R² = 0.0031
10
60 50 40 30 20 10
y = -0.1942x + 440.06 R² = 0.0058
0
0
1990
1994
1998
2002
1990
2006
7c. Holly Blue 80
70
70
60 50 40 30 20 10
y = -0.1779x + 415.73 R² = 0.0079
1998
2002
2006
60 50 40 30 20 10
0
1990
1994
7f. Orange Tip
80
days after March 1st
d ays after March 1st
1998
7e. Green-veined White
7b. Peacock
80
1994
y = -0.1779x + 415.73 R² = 0.0079
0
1994
1998
2002
2006
1990
1994
1998
2002
2006
Figure 7. First appearance dates each spring, 1992–2007, relative to days after March 1st start date Seasonal Abundance Patterns of Common Species For the 19 most frequent species, bar charts (Figures 8–11) show how their numbers changed throughout the year; by displaying their aggregated weekly index scores, with dates indicating weeks beginning. They also reveal clearly the timings, flight periods and relative abundance of different generations or broods in the year. These are annotated in the following species accounts; for the 11 scarcer species. The species order follows that used in the latest Suffolk butterfly atlas (Stewart, 2001). Small Skipper: Ones and twos occurred in 12 years over an 8-week season, between 29 June and 25 August. Most sightings were between 12–25 July. Large Skipper: Noted annually since 1994, usually as single specimens. Its 8-week season, from 18 June to 4 August, was earlier than that of the Small Skipper. Most were seen between 5–18 July.
Trans. Suffolk Nat. Soc. 44 (2008)
BUTTERFLIES AT HENSTEAD 1997–2002
35
Large White: Season extended from late April to late October, but very scarce or absent until mid-July when rapid increase to a peak lasting until mid/ late August (Fig.8a). Pattern largely reflects migrant arrivals in two influx summers of 1992 and 2005. Up to 80 present at one time in 1992. Small White: Season and pattern similar to larger species but with a fairly distinct small spring (May) peak and a later main peak in late August/early September (Fig. 8b). 160
8a. Large White 140
Cumulative index
120 100 80 60 40
Nov. 1 Nov. 1
Nov.…
Oct. 11
Sep.… Sep. 20
Oct. 11
Aug.…
Aug. 9 Aug. 9
Aug. 30
Jul. 19
Jun. 28 Jun. 28
Jul. 19
Jun. 7 Jun. 7
May.…
Apr. 26
Apr. 5
Mar.…
Feb. 1
0
Feb.…
20
60
8b. Small White Cumulative index
50 40 30 20 10
Nov. 22
May. 17
Apr. 26
Apr. 5
Mar. 15
Feb. 22
Feb. 1
0
Figure 8. Seasonal variations in abundance of pierid (white) butterflies, 1992–2007
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36 25
8c. Green-veined White 20
Cumulative index
15
10
5
Nov. 8
Dec. 6
Oct. 25
Nov. 8
Nov. 22
Oct. 11
Sep. 27 Sep.…
Oct. 25
Sep. 13 Sep.…
Oct. 11
Aug. 30 Aug.…
Aug. 2
Aug. 16
Aug. 2
Aug.…
Jul. 5
Jul. 19
Jul. 5
Jul. 19
Jun. 7
Jun. 21 Jun. 21
May. 24
Apr. 26
May. 10
Mar.29
Apr. 12
Mar. 1
Mar. 15
Feb. 1
Feb. 15
0
25
8d. Orange Tip
15
10
Dec. 6
Nov.…
May.…
Jun. 7
May.…
Apr. 26
Apr. 12
Mar.…
Mar.29
Feb. 1
0
Feb.…
5
Mar. 1
Cumulative index
20
Figure 8. Seasonal variations in abundance of pierid (white) butterflies, 1992–2007 Green-veined White: Season from early April into mid-October. Two broods clearly show a smaller but extended spring cohort (peak in May) is separated, by a two week absence in late June/early July, from the main period of abundance peaking from late July to end of August (Fig. 8c) before a steady decline through September. Orange Tip: Ones and twos (nearly all males) visited regularly during its 10week spring season from mid-April into early June, with a marked peak in mid-May (Fig. 8d). A very late male was seen on 20 June (2005) after a cold spring. Small Copper: A sporadic visitor with a few sightings most years, between early May and mid-October, which form 3 clusters indicative of broods - in May–June, July to mid-August, and September to early October (Fig. 9a). These clusters could reflect the triple-brooded breeding of this species in Suffolk (Stewart, 2001).
Trans. Suffolk Nat. Soc. 44 (2008)
BUTTERFLIES AT HENSTEAD 1997–2002
37
8
9a. Small Copper 7
Cumulative index
6 5 4 3 2 1
Nov. 1 Nov. 1
Nov. 22
Oct. 11
Sep. 20 Sep.…
Oct. 11
Aug. 30
Aug. 9 Aug. 9
Aug.…
Jul. 19
Jun. 28 Jun. 28
Jul. 19
Jun. 7 Jun. 7
May. 17
Apr. 26
Apr. 5
Mar. 15
Feb. 22
Feb. 1
0
25
9b. Holly Blue
Cumulative index
20
15
10
Nov.…
May.…
Apr. 26
Apr. 5
Mar.…
Feb. 1
0
Feb.…
5
Figure 9. Seasonal variations in abundance of lycaenid (blue) butterflies, 1992–2007 Holly Blue: An interesting species, occurring between early April and late September, and showing a clear bimodal pattern of two broods – in spring (April–May) and in summer (July–August) separated by a virtual 2-week absence in late June (Fig. 9b). The spring index is rather larger but both broods have similarly protracted flight periods. Up to 7 present at one time. Common Blue: Although an irregular visitor between late May and midSeptember, and not recorded in 6 years, there were clearly two periods of occurrence separated by a scarcity or absence for much of July (Fig. 9c). This pattern conforms to this blue being double-brooded in Suffolk (Stewart, 2001).
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38 12
9c. Common Blue 10
Cumulative index
8
6
4
Nov.…
Nov. 1
Oct. 11
Sep.…
Aug.…
Aug. 9
Jul. 19
Jun.…
Jun. 7
May.…
Apr. 26
Apr. 5
Feb. 1
Feb.…
0
Mar.…
2
Figure 9. Seasonal variations in abundance of lycaenid (blue) butterflies, 1992–2007 Red Admiral: Season from early May until early November, and exceptionally into early December (Fig. 10a). Scarce in spring and early summer but then a steady increase from mid-July to reach a peak in September. Up to 22 present at one time. 100 90
10a. Red Admiral
80
Cumulative index
70 60 50 40 30 20 10
No v. 22
No v. 1
Oct. 11
Sep. 20
Aug. 30
Aug. 9
Jul. 19
Jun. 28
Jun. 7
May. 17
Ap r. 26
Ap r. 5
Mar. 15
Feb. 22
Feb. 1
0
Figure 10. Seasonal variations in abundance of vanessid butterflies, 1992–2007
Trans. Suffolk Nat. Soc. 44 (2008)
BUTTERFLIES AT HENSTEAD 1997–2002 50
39
10b. Painted Lady
45
Cumulative in dex
40 35 30 25 20 15 10
No v. 1
Nov. 1
No v.…
Oct. 11
Sep .…
Sep. 20
Oct. 11
Aug .…
Aug. 30
Aug. 9
Jul. 19
Jun.…
Jun. 7
May.…
Apr. 26
Apr. 5
Feb. 1
Feb.…
0
Mar.…
5
250
10c. Small Tortoiseshell Cumulative index
200
150
100
Nov. 22
Aug. 9
Jul. 19
Jun. 28
Jun. 7
Apr. 26
Apr. 5
Mar. 15
Feb. 22
Feb. 1
0
May. …
50
Figure 10. Seasonal variations in abundance of vanessid butterflies, 1992–2007 Painted Lady: Immigrants have appeared in 14 of the 16 years at various times between early May and mid-October, but with most in late July and August (Fig. 10b). A small spring peak from late May to mid-June is also discernible. Most data were from the major influx summers of 1996 and 2003. Up to 27 present at one time in 1996. Small Tortoiseshell: A much extended season from mid-February to late November (Fig. 10c). Unexpectedly scarce every spring and early summer until mid-July, when a small increase is followed by a very rapid rise to a peak from mid-August to mid-September followed by a rapid disappearance, many presumably then entering hibernation. The summer index is 40–50 times greater than the spring index. Up to 58 present at one time in 1997.
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Peacock: Although seen most years almost continuously between mid-March and late October, its numbers are very low until late July when an ‘explosive’ increase occurs over a few days to reach a short-lived peak from late July to mid-August (Fig. 10d). Most have disappeared by the end of August, many apparently into early hibernation (Stewart, 2001). The summer index is 40–50 times greater than the spring index. Up to 41 present at one time in 1997. 300
10d. Peacock 250
Cumulative in dex
200 150 100 50
Aug . 9
Aug. 30
Sep. 20
Oct. 11
No v. 1
Nov. 22
Aug. 30
Sep. 20
Oct. 11
Nov. 1
Nov. 22
Jul. 19
Jun. 28
Jun . 7
May. 17
Apr. 26
Apr. 5
Aug. 9
45
Mar. 15
Feb. 22
Feb. 1
0
10e. Comma
40
Cumulative index
35 30 25 20 15 10 5
Jul. 19
Jun. 28
Jun. 7
May. 17
Apr. 26
Apr. 5
Mar. 15
Feb. 22
Feb. 1
0
Figure 10. Seasonal variations in abundance of vanessid butterflies, 1992–2007 Comma: Season from late March to early November. Scarce ex-hibernation in spring (7 records), it then shows a bimodal pattern of occurrence (Fig. 10e) with a smaller summer cohort peaking in late July and early August clearly followed by a larger cohort in September; latter fades away through October with rare stragglers into early November. This pattern seems to correspond with the two broods produced in Suffolk (Stewart, 2001).
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Speckled Wood: The season of this recent colonist is currently from midApril to late September. Scattered spring and early summer sightings precede the main period of visits in late summer and early autumn which peaks in early September (Fig. 11a). 12
11a. Speckled Wood
Cumulative ind ex
10
8
6
4
Oct. …
Oct. …
Nov.…
Sep. …
Sep . …
Nov. 1
Aug. …
Aug . …
Aug . 9
Jul. 19
Jun.…
Jun. 7
May …
Apr. …
Apr. 5
Feb. 1
Feb.…
0
Mar.…
2
9
11b. Wall Brown
8
Cumulative in dex
7 6 5 4 3 2
Nov.…
Nov. 1
Aug. 9
Jul. 19
Jun.…
Jun. 7
May …
Apr. …
Ap r. 5
Mar.…
Feb. 1
0
Feb.…
1
Figure 11. Seasonal variations in abundance of satyrid butterflies, 1992–2007 Wall Brown: The scattered sightings of this infrequent visitor between midMay and late October form a clear trimodal pattern (Fig. 11b). The three cohorts have peaks in May, August and late September-October and correspond with the triple-brooded strategy in Suffolk (Stewart, 2001).
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Gatekeeper: Present almost daily during its 9-week season from early July until late August, with peak numbers in late July (Fig. 11c). 90
11c. Gatekeeper
80
Cumulative index
70 60 50 40 30 20
Nov.…
Dec. 6
Nov. 8
Oct. 25
Sep.…
Oct. …
Sep.…
Sep . …
Oct. 11
Aug.…
Sep . …
Oct. …
Aug.…
Aug . …
Aug. 2 Aug. 2
Aug . …
Jul. 5
Jul. 19 Jul. 19
Jun. 21
Jul. 5
May.…
Jun. 7
May.…
May …
Apr. 26 Ap r. …
May …
Apr. 12 Ap r. …
Mar.…
Mar.29
Feb.…
Feb. 1
0
Mar. 1
10
14
11d. Ringlet 12
Cumulative in dex
10 8 6 4
Dec. 6
Nov.…
Nov. 8
Jun.…
Jun. 7
Mar.…
Mar.29
Mar. 1
Feb. 1
0
Feb.…
2
Figure 11. Seasonal variations in abundance of satyrid butterflies, 1992–2007 Ringlet: The short (7-week) season from late June to early August has a distinct peak in early and mid-July (Fig. 11d ). These dates correspond well with the brief flight period in Suffolk (Stewart, 2001). Meadow Brown: Has a 14-week season from mid-June into early September with a clear peak in late July (Fig. 11e), a little earlier than that of Gatekeeper.
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43
11e. Meadow Brown
Cumulative index
40 35 30 25 20 15 10 5
Nov. 22
Nov. 1
Oct. 11
Sep. 20
Aug. 30
Aug. 9
Jul. 19
Jun. 28
Jun. 7
May. 17
Apr. 26
Apr. 5
Mar. 15
Feb. 22
Feb. 1
0
Figure 11. Seasonal variations in abundance of satyrid butterflies, 1992–2007 Scarcer Species Occurrences The following 9 species were erratic or rare visitors to the garden: Brimstone (7 records of males in 6 years from 30 March to 26 September), Green Hairstreak (7 between 27 April to 17 June, with 5 in 1997 and 2 in 1999), Brown Argus (5 in August to September of 1997 and 2006), White-letter Hairstreak (3 records 13–27 July ), Grayling (2, singles in late August of 1999 and 2001), White Admiral (2 seen in July of 2001 and 2006), Queen of Spain Fritillary (netted on 13 September 1997, photographed and verified by R. Walden) and, surprisingly, just single sightings of Clouded Yellow (29 June 2002) and Essex Skipper (July 2004). Nectar plants utilized Observed feeding preferences of different butterfly species in the garden are summarised in Table 5. This shows the relative importance for butterflies of the 14 flowering plant species that were used as nectar sources progressively from spring (left) to late autumn (right). In spring, few butterflies fed in the garden perhaps owing to limited nectar resources then. However, over-wintered vanessids as well as newly emerged Holly Blues, Green-veined Whites and Orange Tips were very mobile – as if primarily seeking mates. In early summer, however, the two flowering Hebe bushes attracted 6 species and were especially important for Ringlets, Gatekeepers and first-brood Commas. In high summer, as expected, buddleia flowers attracted most (11) species and were the primary food source for four vanessids and the two ‘cabbage white’ species. Indeed, Painted Lady (up to 25 together on one bush in 1996), Peacocks and Large Whites depended almost exclusively on buddleia nectar whereas Red Admirals, Small Tortoiseshells and Commas used a wider range of flowers. Two vagrant White Admirals, two Graylings and two White-letter Hairstreaks also appeared on buddleias. The herb Oregano was an equally important nectar plant in summer. It attracted 12, predominantly small, species and was particularly important for Gatekeepers.
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Table 5. Nectar Sources used by Butterflies in the Henstead Garden Rotting Pears Aster Ivy Sedum Eucalyptus
Verbena bonariensis
Salvia superba Herbs spp. Oregano
O
Potentilla fruticosa
Buddleia Bramble
Small Skipper O Essex Skipper Large Skipper O Clouded Yellow Large White Small White Green-veined White F Orange Tip F Green Hairstreak White-letter Hairstreak Brown Argus Common Blue Holly Blue Small Copper White Admiral Red Admiral Painted Lady Small Tortoiseshell Peacock Comma Speckled Wood Grayling Gatekeeper Meadow Brown Ringlet Butterfly species 2 2
Philadelphus
Geranium pratense Hebe Escallonia Lychnis Honesty
Plant species arranged in approximate flowering sequence : spring to left, autumn to right
Total Plants 3 1 1
O O
O O
P O P
O
O
O
O O
O O O
O O
O
1 2 7 5 2 1
O O
O O O O O O O O
O
F O
O P P
O
O O
M P F
O O
M F M 5 6 3
O F O O
O O M F P O F O
O
O O F O F O M P O O O
M O O F O O O
1 4 11 1 12 5 4
4
2 1 2 3 3 1 8 4 9 1 6 1 1 5 5 3
3 4 3 7 2
P primary/exclusive source; M major source; F frequent source; O occasional source
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In autumn, flowering ivy, ice-plants (Sedum) and Aster were vital for remaining vanessids while rotting windfall wild pears sometimes fed stragglers of Red Admiral and Comma into November. A large Eucalyptus tree that flowered prolifically some years in September proved very attractive for up to 10–15 Red Admirals in 2000 and 2005, together with an occasional Small Tortoiseshell and Peacock. Discussion In the 1994 Suffolk garden butterfly survey several correspondents reported 21 or 22 species frequenting individual rural gardens of 0·25–1 acre that were sheltered and planted with nectar sources (Stewart, 1995). The more typical good rural and suburban gardens attracted 17–19 species. Thus, our Henstead garden, with 28 species recorded, including 22 in the best years, attracts a good diversity of butterflies despite being only moderately sheltered and adjoining arable farmland. This was the clearest reward for our efforts to increase nectar sources and improve shelter. Many butterflies fluctuate widely in numbers between years, as shown by standard transect counts in breeding habitats (Asher et al., 2000). At Henstead, the indices of annual abundance (cumulative scores) show that our garden butterflies fluctuated from year to year often by factors of 10 or higher. However, a lack of synchrony between even related species – except maybe for Red Admiral and Comma – is perhaps surprising. For ‘classic’ migrants from the Continent, notable Painted Lady influxes show clearly in the hot summers of 1996, 2003 and 2006, while Red Admirals were plentiful in 1995, 2000 and 2001. The poorest of the 16 years were undoubtedly 1993 and 2005, whereas 1997 produced probably the best show of butterflies. Upward trends in total numbers are apparent for the Comma and Red Admiral, while a rapid increase since 1998 in Speckled Wood reflects its recent spread into north Suffolk. The marked cyclical pattern of the Holly Blue is also clearly demonstrated. Some common butterflies, however, have declined during this study (notably Wall Brown and Small Tortoiseshell) while others varied irregularly without trends. These findings appear to be broadly consistent with national and regional changes for these species. It would seem that beneficial effects of ‘gardening for butterflies’ were often over-ridden by fluctuating life cycle, weather and habitat factors that drive population changes on a wider geographical scale. Such causes of annual variability are still poorly understood even for the commonest butterflies (Asher et al., 2000). A lack of trends for some species could also be due partly to the site location and species behavioural factors. Firstly, butterfly numbers in the garden at any one time may be governed by its finite nectar resources and by their spatial distribution, i.e. the ‘carrying capacity’ of the garden. Secondly, some spring species, notably Green-veined White and Orange Tip, responded little to garden nectar sources and were usually only non-stop transients through the garden. They therefore had higher daily turn-over rates than could be measured by the spot-count recording method. Thus, their abundance indices were probably under-estimated compared with those of more ‘sedentary’ (feeding) butterflies such as Peacock and Gatekeeper.
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Evident limitations of this recording method for monitoring the ‘health’ of the more widespread butterfly populations could (as with individual transects) be a function of scale and location. That could be overcome (as for national garden bird surveys) by setting up a network of ‘garden butterfly observatories’ across a county or greater area. Seasonal occurrence patterns are well described graphically by the recording method used here. They conform also to generalized diagrams and accounts in the literature (Mendel & Piotrowski, 1986; Thomas & Lewington, 1991) but add far more interesting details. Most species were scarce or absent in spring, when only Orange Tip, Green-veined White, and Holly Blue showed a strong peak, and Peacock a small peak. The Orange Tip, of course, is unusual for being a purely vernal species. Highest numbers and diversity occurred from late July into mid-August (Figs. 6 and 7–11) when the dominant species were Large White and Peacock. July was also the peak time for Gatekeeper and Meadow Brown, while late August and September were the prime period for Small Tortoiseshell, Comma and Red Admiral. Each spring, butterfly watchers eagerly await the first appearances of overwintering adults from hibernation. The Henstead garden records not only measured the high annual variability of these events but also indicated no statistically significant trends in appearance dates during the 16 years of this study. The latter finding seems contrary to phenological trends reported from other regions (Butterfly Conservation Society reports). Such non-conformity might be a local effect, stemming from the slower spring warming (also producing later flowering and leaf-burst) usually experienced in coastal northeast Suffolk compared to the more rapidly warming inland districts of the county and of the wider East Anglian countryside. A similar picture was also noted (anecdotal records) for the same species’ spring appearances in the nearby Henstead hedgerows and water meadows, though first dates there typically preceded those in the garden by 1–3 days. This semi-quantitative method enables garden butterfly-watchers to gain fascinating insights into how their local butterfly communities change through the seasons, as well as from year to year. It also could contribute useful supplementary data for conservationists assessing the wider picture. Acknowledgements My thanks are due to Dr. Geoff Gibbs (formerly of the Essex Wildlife Trust) for supplying the E.W.T. butterfly recording form that became the template for my own system. Rob Parker (Suffolk Naturalists’ Society) provided encouragement and helpful comments on an earlier draft of this report. References Asher, J., Fox, R., Harding, P., Jeffcoate, G . & Jeffcoate, S. (2000). The Millennium Atlas of Butterflies in Britain and Ireland. Oxford University Press, Oxford. Mendel, H. & Piotrowski, S. H. (1986). The Butterflies of Suffolk. Suffolk Naturalists’ Society, Ipswich. Stewart, R. G. (1994). Recording butterflies in an Ipswich garden, 1980–1993. Trans. Suffolk Nat. Soc. 30: 15–17.
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Stewart, R. G. (1995). The Suffolk garden butterfly survey, 1994. Trans. Suffolk Nat. Soc. 31: 6–13. Stewart, R. G. (2001). The Millennium Atlas of Suffolk Butterflies. Suffolk Naturalists’ Society, Ipswich. Thomas, J. & Lewington, R. (1991). The Butterflies of Britain and Ireland. Dorling Kindersley, London. Dr. Peter J. Dare 2 Corn Hill, Back Road Wenhaston Halesworth Suffolk. IP19 9BW
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