RSPB/NE Countdown 2010: Bringing Reedbeds to Life Project
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RSPB/NE Countdown 2010: Bringing Reedbeds to Life Project Wildlife surveys CHAPTER 6: Light trap surveys for moths C J Hardman With helpful comments on draft by Mark Parsons (Butterfly Conservation) Contents Summary ............................................................................................................................................. 1 METHODS ............................................................................................................................................... 2 Light trap survey field methods .......................................................................................................... 2 Analysis methods ................................................................................................................................ 5 RESULTS ................................................................................................................................................ 10 What moth species were found on the three reedbed reserves? ........................................................ 10 Species composition ......................................................................................................................... 13 What habitat variables were reedbed specialist moths associated with? ....................................... 14 What habitat were internal reed-feeding moths associated with? .................................................. 19 What habitat were wetland specialist moths associated with? ....................................................... 24 How did the number of reedbed and wetland specialist Lepidoptera compare between the wettest and driest areas? ................................................................................................................. 29 How did the number of reedbed and wetland specialist Lepidoptera compare between old and new areas? ........................................................................................................................................ 30 What reedbed habitat conditions were associated with maximum number of Lepidoptera species at the survey sites? ........................................................................................................................... 35 What habitat variables were associated with moths with a conservation status? .......................... 46 Composite habitat variables ................................................................................................................. 49 References ............................................................................................................................................ 50 Summary Twelve light traps were set at each of three key reedbed sites (Hickling Broad in Norfolk, Ham Wall in Somerset and Stodmarsh in Kent). Each trap was set three times, at intervals of three weeks between June and August 2010. Over all surveys at all sites 5 524 individuals and 202 species were trapped. Of the 202 species trapped, 16 species were classified as reedbed specialists and 47 as wetland specialists, according to expert opinion based on agreed definitions. Two Endangered (RDB 1) species were trapped (Clostera anachoreta and Pelosia obtusa) three Vulnerable (RDB 2 & pRDB 2) species (Cnephasia genitalana, Monochroa divisella and 1 Phragmataecia castaneae), three Rare (RDB 3 & pRDB 3) species (Chortodes brevilinea, Pelosia muscerda and Yponomeuta rorrella) and 12 Nationally Scarce species. 20 UK BAP moth species were trapped: one being a reedbed specialist: Chortodes brevilinea (Fenn’s Wainscot) and 19 being widespread but rapidly declining species. In total, 135 moth species were caught at Hickling Broad, 78 at Ham Wall and 128 at Stodmarsh. Hickling Broad not only had higher overall species diversity, but also had a higher number of species of conservation interest and reedbed specialists. Stodmarsh had high numbers of wetland specialist moths. Ham Wall was lower than the other two sites for all measures of moth diversity. Habitat variables measured around the traps were tested to see which best explained variation in number of species caught in traps. Because of the differences in moth diversity between sites and differences in geography between sites, general conclusions are sometimes constrained by site differences overriding trends in other habitat variables. These habitat associations should be interpreted with caution due to the site differences and the small sample size (12 traps at each site). However they provide a good starting point indicating which potential relationships would be interesting to investigate further. A study with more traps at sites in a similar geographic area (e.g. only the Broads) would be an interesting next step. Traps that had a high overall diversity of moth species tended to be in places where the litter was not fully submerged in the four months before trapping and where there was a high diversity of plants. Moths with a conservation score tended to be trapped at points with high plant species richness and litter that was not fully submerged before surveys. • Higher numbers of wetland specialists were trapped at points with fully submerged litter, more standing water, deeper litter and greater stem densities. Higher numbers of reedbed specialists were trapped at points with deeper litter, standing water, further from scrub, with high stem densities. Higher numbers of internal reed feeders were trapped at points with deeper litter, standing water and thicker reed. Areas of reedbed at Hickling and Stodmarsh that were restored in 1998 had similar numbers of reedbed and wetland specialist moth species to much older areas of the sites. Small Dotted Footman, Pelosia obtuse, (Endangered), Reed Leopard, Phragmataecia castaneae, (Vulnerable) and Fenn’s Wainscot, Chortodes brevilinea, (UK BAP Priority Species, Rare) were all trapped in the Hundred Acre reedbed (12 years old) at Hickling Broad along with 8 other Rare or Nationally Scarce moth species. METHODS Light trap survey field methods A subset of water trap points were surveyed for moths in 2010 using light traps. 12 points out of the 21 water trap points at each site were randomly selected and the final selection was adjusted to ensure all hydrological categories had been covered. Since hydrological data had already been collected in 2009 at the sampling points, these data were used to ensure a mix of hydrological strata were sampled. Surveys were spread over three sessions, detailed below. Session 1: 21-25 June (Stodmarsh); 28 June – 2 July (Hickling); 5-9 July (Ham Wall) Session 2: 12-16 July (Stodmarsh); 19-23 July (Hickling); 26-30 July (Ham Wall) 2 Session 3: 2-6 August (Stodmarsh); 9 – 13 August (Hickling); 16-20 August (Ham Wall) Four traps were set up each night before dusk and checked at 6 am the following morning. The groups of four were changed each week with a mixture of hydrological strata being surveyed each week. Trapping was only done on suitable nights without high wind or heavy rain as these conditions can affect catches. Heath type 15 W actinic traps were used, supplied by Anglia Lepidopterist Supplies. They were fitted with rain-guards and used 12 Amp hour batteries, attached to the poles to stay dry. One large egg box tray (roughly 30cm square) ripped into six pieces lined the base of the trap. Traps were fitted firmly to platforms on top of wooden poles as in the water trap survey and the height of the pole was recorded in order to account for this in analysis. Traps were turned on by a light sensor and this mechanism was tested during every set up. The reed in 1 m radius around the trap was flattened at each location to standardise immediate habitat influence. Figure 6.1: Moth trap in situ (Chris Nall) The following morning, moths were identified in situ by ecological contractors (Hickling Broad: Jon Clifton and Jim Wheeler, Stodmarsh: Sean Clancy, Ham Wall: James McGill). Only moths found inside the trap were recorded. All species were identified and the number of individuals of each species was counted. Each morning a basic habitat survey was carried out. This involved recording live and dead reed height, whether there was standing water in the vicinity and the standing water level in the core. Weather reports were completed after trap set up and before and after trap checking each morning. Donna Harris, Chloe Hardman, Chris Nall and Stephen Gregory carried out surveys with the ecological contractors. Surveys were designed by Donna Harris with advice from Mark Parsons (Butterfly Conservation). Further habitat surveys During the first trapping session, litter was measured 0.5m into reeds from the core edge, in each of NE, SE, SW, NW directions. In the same directions, 1 m into reeds, standing water level (surface to boot sole) was measured. Plant species were recorded in four 50 x 50cm quadrats 2m from the core edge. On the second trapping session, at 1m into reeds from core edge, in each of N, E, S, W directions, standing water level (surface to boot sole) was measured. Then, also at 1m into reeds, using a 50 x 50cm quadrat, number of live and dead stems (above chest height) and the number of panicles was measured. Four randomly selected stem base diameters from within the quadrat were measured using callipers. On the third trapping session, at 1.5m from core edge, in each of N, E, S, 3 W directions water height (surface to boot sole) was measured. All survey equipment was collected up in this session. Locations of the survey points Figure 6.2: Map of moth trap