Hunter’s Bog Butterfly Transect 2005

Introduction

The document provides a species account of the Lepidoptera of Hunter’s Bog, Holyrood Park, Edinburgh for the summer 2005 season. As such it provides abundance indices for the commonest species, based on the methods of Pollard employed for the Butterfly Monitoring Scheme (BMS, 2005). It is a summarised version of the original excluding as it does the recommendations for further work, the detailed species records and the maps showing the location of the transect itself. A full length electronic copy can be obtained from the author.

Background

Two existing BMS transects, one based on Salisbury Crags and the other on Dunsapie Loch, have been in place in Holyrood Park since 1989. Although some gaps in the record exist between 1991 and 2000 they have nonetheless provided a valuable view of the key Butterfly and Moth species frequenting the semi-natural grassland and rock-face habitats of the park.

However, subsequent to their selection, the Hunter’s Bog area was allowed to revert to a more original state. While it had been qualitatively identified as a habitat supporting significant numbers of Ringlet Butterflies (Aphantopus hyperantus) and a Six spot Burnett Moth (Zygaena filipendulae) colony (personal observation) , no quantitative survey work had taken place since then.

Aims and objectives

To undertake a survey of Hunter’s Bog to identify the Lepidoptera present and provide abundance indices for those species in the summer 2005 season.

Methodology

Survey Area

The principal habitat present in Hunter’s Bog is classified as Dry semi/unimproved acid grassland, within the European Nature Information System / Butterfly Conservation (BMS, 2005) system, with some sections where Seasonally wet and wet marshy grasslands provide the secondary habitat bordering the transect.

Exclusions

Time constraints resulted in the survey work finishing on 16/09/2005. Similarly, visits could only be made in 14 out of the 29 weeks defined by the BMS.

Methods and equipment

A transect was established through Hunter’s Bog and divided into 6 sections, each combining different aspects of vegetation, exposure and drainage. It should be noted that the transect has been extended out of Hunter’s Bog at its north end to incorporate some known populations of Small Copper (Lycaena phlaeas) and Common Blue (Polyommatus icarus) butterflies. The overall length of the transect is 1.9 kilometres. Please note that while Holyrood Park is a site of Special Scientific Interest this does not guarantee unrestricted access to any of the areas mentioned.

Surveys were carried out in line with the weather condition parameters employed for the BMS (BMS, 2005). Counts were only made under suitably warm and bright weather conditions, when wind speeds were light, and where possible between the hours of 11am and 3.45pm. The minimum BMS criteria are either 13-17ºC with at least 60% sunshine, or 18+ºC without rain (can be cloudy). The BMS study period runs from the last week in March to the third week in October and proposes weekly visits to the site.

The numbers of Lepidoptera in each transect section were counted by employing a 5 bar gate method, the totals being subsequently entered on Butterfly Survey pro-forma developed by Historic Scotland. The transect was walked at approximately 1.5 miles per hour, and due to the width of the path followed, along with the nature of the surrounding vegetation, all Lepidoptera within 5 metres of the observer were counted.

Binoculars (Swarovski EL 8.5x42) were used to examine the Lepidoptera seen and the species identification was subsequently checked against Butterflies of Great Britain and Ireland (Lewington, 2004).

Analysis methods employed

The survey data was entered into the BC Transect Walker application in order to automate the calculation of annual abundance indices.

Results

Totals seen and abundance indices by species

Ringlet – 444 (573)
Meadow Brown (Maniola jurtina) – 194 (239)
Small Copper – 126 (205)
Common Blue (Polyommatus icarus) – 29 (35)
Small Heath (Coenonympha pamphilus) – 19 (28)
Six-spot Burnet – 11 (15)
Small White (Pieris rapae) – 9 (13)
Grayling (Hipparchia semele) – 8 (11)
Green-veined White (Pieris napi) – 3 (5)
Small Tortoiseshell (Aglais urticae) – 3 (3)
Red Admiral (Vanessa atalanta) – 1 (1)
Peacock (Inachis io) – 3 (none calculated)

Discussion

The initial qualitative view of the site as an important place for Ringlet was confirmed, with Meadow Brown, Small Copper and Common Blue being the next most common butterflies present. Previously held opinions on likely 6 Spot Burnet populations were not matched by the results for this breeding season. However other Burnet colonies within the park seemed to hold their usual numbers (personal observation).

The relatively dry conditions during the summer resulted in small numbers of Grayling moving down into the bog from the higher slopes, an effect only previously noted during the very dry conditions of summer 2003 (personal observation).

Small Copper illustrated its usual extended breeding season (Lewington, 2004). However it should be noted that although they seem to rely heavily on Ragwort (Senecio jacobae) as a late season source of nectar, this plant is considered to b a problem species within the park (Joe Muir (Historic Scotland Park Manager), personal communication).

Conclusions

The summer 2005 Lepidoptera survey of Hunter’s Bog established the presence of twelve species. This list included Six spot Burnett Moth (Zygaena filipendulae) and Common Blue (Polyommatus icarus), both priority species within the local biodiversity action plan (EBAP, 2004). In terms of abundance three species, namely Ringlet (Aphantopus hyperantus), Meadow Brown (Maniola jurtina) and Small Copper (Lycaena phlaeas) accounted for 90 percent, by total, of the Lepidoptera seen.