Technical Annex 22.11: Drumochter Hills SPA – Merlin ... · Technical Annex 22.11: Drumochter...

Proposed Beauly to Denny 400kV Overhead Transmission Line Technical Annex 22.11 Drumochter Hills SPA – Merline Special Study

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Technical Annex 22.11: Drumochter Hills SPA – MerlinSpecial Study

22.11 Scope of Special Study

22.11.1.1 The scope of this special study is to assess the effects of the construction, operation anddismantling phases of the proposed 400kV overhead transmission line and dismantling of theexisting 132kV overhead transmission line on merlin (Falco columbarius) as a qualifyingspecies within the Drummochter Hills SPA (see Figure 22.11). The assessment is specificallyrelated to any adverse effects the project may have on site integrity.

22.11.1.2 Potential impacts on dotterel (Charadrius morinellus) have been scoped-out due to theirmontane habitat requirement, resulting in no spatial overlap with the proposed project.

22.11.2 Designation of Study Site and Conservation Objectives

22.11.2.1 The Drumochter Hills site qualifies as an SPA under Article 4.1 of the Directive 79/409/EEC bysupporting populations of European importance of the following species listed in Annex I of theDirective:

• Merlin - 7 pairs representing at least 0.5% of the breeding population in Great Britain(count as at mid 1990s).

• Dotterel - 70 pairs representing at least 8.3% of the breeding population in Great Britain(count as at mid 1990s).

22.11.2.2 The following provides the conservation objectives of the Drumochter Hills SPA:

• To avoid deterioration of the habitats of qualifying species (merlin, dotterel), or significantdisturbance to the qualifying species, thus ensuring that the integrity of the site ismaintained.

• To ensure for the qualifying species that the following are maintained in the long term:• Population of the species as a viable component of the site;• Distribution of the species within the site;• Distribution and extent of habitats supporting the species;• Structure, function and supporting processes of habitats supporting the species; and• No significant disturbance of the species.

22.11.3 Description of Study Site

22.11.3.1 The Drumochter Hills are located either side of the Drumochter Pass in the central Highlandsof Scotland. On the western side of the Pass the SPA extends from Dalnaspidal in the south toBalsporran Cottages in the north and westwards to the banks of Loch Ericht, and on the eastside from Dalnaspidal to Dalwhinnie and eastwards to the summits around Cama’ Choire. Thehills consist of gently rounded summits, generally between 900-950m, though the fullaltitudinal range of the area is 360-1010m. The hills are divided by steep-sided gullies as wellas by the Pass of Drummochter. The Drumochter Hills are also designated as a SAC due tothe presence of European dry heaths, alpine and boreal heaths, sub-Arctic Salix spp. scrub,siliceous alpine and boreal grasslands and blanket bogs.

22.11.4 Summary of Proposed Project

Location

22.11.4.1 The route of the proposed overhead transmission line follows the existing infrastructurecorridor through the Drumochter Pass containing the A9 road, railway line and the existing


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132kV overhead transmission line. The proposed 400kV line runs approximately parallel to,just east of, the existing 132kV transmission line and crosses the SPA for approximately6.4km between North Drumochter Lodge and Dalnaspidal. The exising 132kV line crossesapproximately 2.1km of the SPA (see Figure 22.11).

Structural Development

22.11.4.2 Drawing A3/PTD/6054/255 and A3/PTD/6054/256 show the routes of the proposed 400kVoverhead transmission line and the 132kV line to be dismantled as part of the project withinthe Drummochter Hills SPA. Section 22.16 provides a method statement prepared by BalfourBeatty Power Networks which details the proposed works within the Drummochter Hills SPA.

22.11.5 Merlin Ecology

Introduction

22.11.5.1 The merlin is a small, dashing falcon (wing span 50-62cm, body size 25-30cm) which breedson moorland, notably in the Scottish Highlands and islands, the Welsh mountains, thePennines and the southern uplands (Gilbert et al. 1998, Cramp 1980) and winters on lowerground or coasts. In the Scottish Highlands, merlins are more abundant on the drier, moreeasterly hills, and are much more thinly spread in the Western Highlands, possibly due topoorer land productivity in the wetter and colder west.

22.11.5.2 Merlin in the UK nest at low density in open habitat: (5-10 pairs per 100km2), either on theground with nests concealed in deep heather, or in old crows nests near to the edge of coniferplantations (Bibby 1986, Newton et al. 1986, Rebecca & Cosnette 2003) and feeding onneighbouring open ground (Gibbons et al. 1993). Although heather grows on ground abovethe 700m contour, climatic factors tend to inhibit growth. The resulting depth of cover therebyprecludes use of these areas by nesting merlin. Territories are traditional, and are usedrepeatedly from year to year by successive generations of birds, although the exact location ofthe nest does vary (Rebecca & Cosnette 2003, Marsden et al. 2003). The nest is a shallowscrape on the ground, lined with small twigs, pieces of heather, bracken and other material.Eggs are laid in late April or May (Rebecca & Bainbridge 1998, Fielding and Haworth 2003).Incubation is for 28-32 days. The female stays close to the nest, and is responsible for most ofthe nest defence, and nearly all parental care. The male provides all food from before egg-laying until after the young fledge. Young in a ground nest will often leave the nest at 18-20days and scatter into the surrounding undergrowth. They fledge at 25-32 days, and areindependent about a month later. One brood a year is raised. Replacement clutches are laidafter early egg loss. Burning of heather may terminate a long series of nesting attempts butthe site may be reoccupied when new cover is sufficiently grown.

22.11.5.3 Merlin require extensive open ground for hunting and take a wide range of small birds (Bibby1987). Their main prey species are meadow pipits (Anthus pratensis) and skylark (Alaudaarvensis). The merlin hunts by perching in an elevated position to locate their prey, usually onrocks or tree stumps. Once prey is sighted, it is usually caught after a short distance surpriseattack following a low flight from a perch. Other hunting techniques include prolongedpersistent chasing and vertical stooping. A mated pair frequently hunt co-operatively. Prey isusually caught in the air close to or on the ground.

22.11.5.4 Little is known about the hunting distance of breeding merlins (Cramp 1980). Birds tracked byradio telemetry hunted at least 4km from the nest in Wales (Rebecca et al.1990) and foragingflights of six breeding males averaged from 3-5km in an Alaskan study (Schempf 1989). Homeranges of three breeding males in a Montana study were 13, 23 and 28km2, each birdtravelling up to 9km away from its nest. In Grampian, mean minimum distance flown by merlinto hunt ringed lapwing (Vanellus vanellus) chicks was 3.4 +/- 1.1km, with a range of 2.0 to5.6km (Rebecca et al. 1990).


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Population Trends & Conservation Status

22.11.5.5 In the UK widespread declines since the late 19th century are thought to have been caused byhuman persecution, habitat loss and increased disturbance. From the 1950s merlins werebadly affected by organochlorine pesticides, resulting in an all-time population low by 1960 ofabout 550 pairs. Population recovery has been slow, and has been hampered by habitat loss,primarily due to afforestation and overgrazing (e.g. Rebecca & Cosnette 2003). Loss ofmoorland habitat is still a major threat. Sympathetic management of heather moorland andadjacent low intensity agricultural land, and sympathetic management of forests in areaswhere the birds nest, is key to ensuring the survival of the species.

22.11.5.6 Merlin has shown indications of a doubling of population size between the national surveys of1983/4 and 1993/4 (Rebecca & Bainbridge 1998) which may be associated with an increaseduse of forest edge as a nesting habitat (Parr 1994). In some areas it is also thought that springweather conditions could have played a part in this population recovery. In a 2003 study ofhistorical data for a site where no major habitat changes had taken place, Fielding & Haworth(2003) found that the numbers of occupied sites, successful sites and total clutch size werepositively correlated with the degree-days1 between early February and the mean laying date(5th May). Furthermore, the mean number of young fledged was negatively correlated with themaximum temperature for the period immediately after the mean laying date and with theamount of rainfall when nestlings were present (Fielding & Haworth 2003). Poor springweather could effect birds either directly, by preventing birds from reaching peak breedingcondition (Meek 1988), or indirectly by affecting the amount and availability of food (plants andinsects, Fielding & Haworth 2003; passerines, Ratcliffe 1990).

22.11.5.7 Population size in the UK currently stands at around 1300 pairs ± 200 pairs (Rebecca &Bainbridge 1998). Consequently the species has recently been moved from the Red List ofBirds of Conservation Concern but is still listed on the Amber List on the basis of its historicalpopulation decline in the UK during 1800-1995 (Gregory et al. 2002). National merlin surveyswere carried out in 1983-84 (Bibby & Nattrass 1986) and 1993-94 (Rebecca & Bainbridge1998).

22.11.5.8 Merlin is afforded legal protection under Schedule 1 of the Wildlife and Countryside Act 1981and Annex I of the EC Wild Birds Directive 1979 (79/409/EEC).

22.11.6 Assessment Methods

22.11.6.1 The assessment included the following:

• Desk study;• Species specific survey for merlin;• Moorland breeding bird survey;• Summer flight activity survey; and• Information from SNH commissioned merlin survey.

Desk Study

22.11.6.2 Various organisations and local experts, including RSPB, SNH, Cairngorm National Park LocalBiodiversity Action Plan (LBAP) Officer and the Highland Raptor Study Group, were consultedduring the course of the desk study (and during the subsequent stages where necessary), inorder to collate existing information on the historical use of merlin 5km either side of theproposed 400kV overhead transmission line within the Drummochter Hills SPA. A full list of theorganisations consulted and an indication of the level of information provided is listed inSection 22.18 of the Technical Annex.

1 ‘Degree-days’ – a measure of accumulated temperature above a developmental threshold; degree days quantify the amount bywhich daily temperatures exceed this threshold. e.g. If the temperature remained 1° above the lower developmental threshold for24 hours, one degree-day is accumulated.


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Species Specific Survey for Merlin

22.11.6.3 The methodology for species-specific surveys for merlin are prescribed in Bird MonitoringMethods (Gilbert et al. 1998), and were followed for this study. Areas of high suitability forbreeding merlin were initially identified in April 2004 for a corridor of 1km along the proposed400kV transmission line route within the SPA boundary, and outwith the designated site wherethe proposed transmission line is routed along the boundary of the designated site.

22.11.6.4 Identification of suitable breeding areas included defining the following: moorland with old,deep heather; moorland with rocky outcrops; and moorland with old crows nests in plantations(up to 100m from edges and rides) or scattered trees. For all areas confirmed as potentiallysuitable three survey visits were then undertaken between May and July 2004 (inclusive). Soas to ensure no birds were disturbed all potential areas were scanned using binoculars andtelescopes to confirm occupancy by merlin. The species specific survey for merlin involved atotal of approximately 48 hours survey time.

Moorland Breeding Bird Survey

22.11.6.5 In addition to the species specific survey, an adapted moorland breeding bird survey (Brown &Shepherd 1993) was completed to provide additional information regarding the location ofbreeding sites, use of the study site by flighting merlin and prey species.

22.11.6.6 All habitats within the study corridor were surveyed by systematically walking the survey areaso that the area was thoroughly walked such that all parts were visible and not greater than100m from the surveyor. In order to ensure survey effort was constant the study site wasdivided into 500m x 500m quadrats. Each quadrat was surveyed for 20-25 minutes. Wherepotential breeding sites for raptors (e.g. crags, wooded gorges) were encountered thesurveying intensity was increased to ensure detailed scanning of potential nesting sites.

22.11.6.7 All species encountered were mapped on a 1:10 000 field map for each visit. No surveyingwas undertaken in adverse weather conditions, e.g. windy, precipitation, low cloud, etc.

22.11.6.8 Recording methodology followed the standard Common Birds Census (Marchant 1983),including field registration and behaviour codes.

22.11.6.9 Detailed analysis of field maps were undertaken in order to produce final distribution maps ofbreeding birds throughout the study corridor. The following criteria was used to establishwhich birds were actually breeding:

22.11.6.10 For all birds:

• presence of nest, eggs and/or chicks• alarm calling indicative of nest, young or territory• displaying or song-flighting• distraction display• birds aggressively defending territories• birds are seen carrying food to nest or young

22.11.6.11 For divers and ducks:

• birds showing secretive behaviour• presence of pairs, lone males, small groups of males chasing females (ducks only)

22.11.6.12 For all raptors:

• if a pair are apparently attached to a territory

22.11.6.13 For grouse and ptarmigan:

• if a pair were recorded• males in song flight• males in territorial behaviour


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22.11.6.14 For all gulls:

• numbers of pairs were counted•

22.11.6.15 For all passerines:

• birds singing or alarm calling.

22.11.6.16 All flights of merlin seen during the course of the breeding bird survey were recordedaccording to the methods for Summer Flight Activity Surveys (see below).

22.11.6.17 The breeding bird survey involved a total of approximately 70 hours survey time.

Summer Flight Activity Survey

22.11.6.18 A summer flight activity survey was also undertaken to record merlin activity within the studycorridor. Detailed flight observations were carried out from suitable vantage points (VPs),providing optimum viewsheds along the route of the proposed 400kV overhead transmissionline. Each VP involved the study of approximately a 2km corridor length and 1km width beingwatched. Visibility plans, showing the area visible at 27.5m above ground level (representingthe mid-point of average tower height) are provided for all VPs in Figure 22.15.

22.11.6.19 A total of 6 VPs was chosen to ensure complete coverage of the proposed transmission lineroute within the Drummochter Hills SPA. The study involved surveying all 6 VPs along theroute of the proposed transmission line, with a total of two 3-hour watches for each VP beingundertaken per month from April to July 2004 inclusive. This involved a total of 24 hourssurvey time per month per VP. (Total survey time for the study corridor was 144 hours).

22.11.6.20 Survey for this special study involved undertaking day watches, reflecting the major activityperiod for merlin. VPs were undertaken in varying weather conditions, only being finished earlywhere extreme weather conditions or poor visibility prevented data collection. Each watchlasted 3 hours, unless inclement weather prevented completion of the watch.

22.11.6.21 Viewing from VPs is generally recognised to cover a field of view of 180 degrees, and VPlocations were therefore chosen to ensure that the maximum extent of the length of theproposed transmission line fell within this view. During each VP watch the area in view wasscanned constantly using binoculars and telescope until a target species was detected inflight. Target species included others as well as merlin, but only this species is relevant forthis special study.

22.11.6.22 Once detected, the bird or flock was followed until it ceased flying or was lost to view. The timethe bird or flock was first detected and duration of the flight, while in sight, was recorded onstandardised recording forms. (It should be noted that a mean height was estimated forflocks). The route followed by the bird or flock was plotted onto a relevant scale of map (nosmaller than 1:25 000), in the field. The bird’s flying height was estimated at the time ofdetection and at 15 second intervals until lost from view, and was classified as:

• <5m;• 5-60m; or• >60m.

22.11.6.23 The above flight height categories reflect the average height of towers and conductors. Themajority of tower heights will be between 45 and 60m (with the earth wire height at mid spanbeing at least several metres lower than the towers), however, a small number of towers willbe upto 65m in height, again with the earth wire being several metres lower. The conductorwires, mid span, are a minimum of 7.6m above ground level.


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Scottish Natural Heritage (SNH) Merlin Survey

22.11.6.24 In addition to the transmission line route corridor survey for merlin undertaken by HeritageEnvironmental Ltd. (HEL) during April - July 2004, SNH were undertaking a merlin survey ofthe entire SPA (between April and August 2004) as part of site condition monitoring. Theresults of this study, involving approximately 115 hours survey time, have been incorporatedwithin this special study to ensure a comprehensive assessment. This work included recordingthe occurrence of all merlin flights, although details of flight height, duration and direction offlight lines were not recorded.

22.11.7 Suitability of Assessment

22.11.7.1 The assessment included the completion of a comprehensive desk study consultation togather existing information relating to merlin nest sites within the SPA and surrounding areas.The survey elements of the assessment (merlin specific survey, moorland breeding birdsurvey and summer flight activity survey) combined to map and evaluate suitable merlinhabitat, assess flight activity and breeding within the proposed 400kV overhead transmissionline and existing 132kV transmission line study corridor.

22.11.7.2 The merlin specific survey and flight activity surveys were undertaken according to themonitoring methods described by Gilbert et al. (1998), which were in turn based on thoseadopted for the 1993-94 national merlin survey (Rebecca & Bainbridge 1994, 1998). Thegeneric breeding bird survey methodology was aimed at confirming presence of all breedingopen ground birds (including both merlin and their prey species). The approach adapts theConstant Search Method (Brown & Shepherd 1993) for censusing upland breeding birdpopulations. In addition, contexting information regarding merlin abundance, distribution andbreeding status within the Drumochter Hills was taken from a merlin survey of the entire SPA,commissioned in 2004 by SNH as part of site condition monitoring (Cooper & Gallacher 2004).

22.11.7.3 It is not considered that increasing the intensity of VP survey effort or extending the width ofthe study corridor (e.g. from the 1km width used to 2km) would improve the assessment. Thecombination of survey methods and intensity of each individual method ensured acomprehensive assessment that is considered to be appropriate and fit for purpose indetermining the impact of the proposed project on the qualifying features of the DrumochterHills SPA.

22.11.8 Baseline Survey Results

Desk Study Records

22.11.8.1 The desk study provided records of one site within the SPA but outwith HEL’s survey corridorwhere a probable territory was located within grid square NGR NN 62 75 in 2004 and wheremerlin have been seen regularly in previous years, although no breeding was confirmed.

Assessment of Suitable Breeding Habitat within the SPA Study Corridor

22.11.8.2 Within the proposed transmission line study corridor, heather was generally of low value fornesting merlin due to browsing and trampling by red deer (Cervus elephus) and historicalmuirburn practices. No carrion crow (Corvus corone) or hooded crow (C. cornix) nests wereidentified within the route corridor as alternative nesting sites for merlin. However, severalareas of suitable habitat for breeding merlin were noted during the walkover survey (seeFigure 22.11, Table 22.48). These suitable areas were comprised of sheltered burns or gullieswith deep heather to provide potential cover for nesting. No crow nests were found within thearea of coniferous plantation along the A9 corridor, presumably as a consequence ofmoorland predator control.


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Assessment of Breeding

22.11.8.3 The species specific merlin survey and the moorland breeding bird survey confirmed nobreeding or attempted breeding within the proposed transmission line study corridor. Theclosest suspected territory was 1.4km to the west of the proposed route at its closest point.

Assessment of Flight Activity

22.11.8.4 Very low levels of merlin flight activity were detected within the proposed transmission linestudy corridor, with only four flights recorded from all survey methods, indicating no breedingand limited hunting within the study area.

22.11.8.5 The three merlin flights observed during the VP watches along the Drumochter Pass aredetailed in Table 22.49 and Figure 22.11. Three flights out of the four flights recorded from allsurvey methods were outwith the SPA and were very short in both distance and duration, andinvolved birds flying down into the cover of heather. One further flight was seen within the SPAcorridor during the first moorland breeding bird survey on 12th May 2004. This involved a birdflying out of the sightline of the surveyor along a very steep-sided gulley and so the totalduration and direction of flight could not be mapped. This sighting is detailed on Figure 22.11.


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Table 22.48: Target notes relating to potential merlin habitat within the survey corridor of the Drumochter Hills SPA.

TargetNoteNumber

OSsquare Eastings Northings Location Study area Description of habitat

1 NN 63808 82812Drochaid a' Bhacain S ofDalwhinnie to NorthDrumochter Lodge

DrumochterNo crow nests within this plantation strip, no crows observed(probably due to heavy keepering effort)

2 NN 64034 82575 Plantation strip just south ofDalwhinnie Drumochter

Shelterbelt slightly more mature than other strips to N and S,potentially more suitable for crow (& therefore merlin) nest sites.Trees c. 5-7m high.

3 NN 64517 82105

Allt Coire nan Cisteachan - nrtrack leading up moutnainsidejust S of Wade Bridge nrDalwhinnie

DrumochterBurn with shallow heather providing suboptimal habitat formerlin.

4 NN 63505 81576

NOT IN SPA. Far side ofrailway along west side of A9between plantation at WadeBridge and Nrth DrumochterLodge.

DrumochterPatches of scrub/small trees along back of railway line. Merlinwas sighted on fence post along this stretch during May VP. Nofurther signs seen during breeding bird surveys.

5 NN 64305 81186Allt Coire Bhohe, burnbetween North DrumochterLodge and Wade Bridge

DrumochterSteep sided burn with scattered trees and fairly deep unburntheather. Provides good habitat for merlin, although no merlinsigns were seen.

6 NN 63300 80379Plantation strip along roadsidenorth of North DrumochterLodge

Drumochter

Shelterbelt along existing transmission line with conifers 4-5mhigh and overgrown heather. No signs of crow nests or merlin. [*barn owl pellet found here in hollowed out top of deer fence postduring early September '04).

7 NN 63989 79790Small plantation stand onoppostite side of road fromNorth Drumochter Lodge

DrumochterNo crow nests were located within this plantation strip, no merlinsigns.

8 NN 63280 79300 Allt Coire Dubhaig south ofNorth Drumochter Lodge. Drumochter

Several scattered birch trees growing up the streamside withdeep, overgrown heather. Sheltered. No crow nests in trees. Nomerlin signs seen, although the pathways around the back ofNorth Drumochter Lodge are degraded and obviously used quitefrequently by vehicles - disturbance may discourage breeding


Technical Annex 22.11 - 9

merlin.

9 NN 62486 79181 Gulley south of BalsporranCottages Drumochter

Steep sheltered gulley; deep heather with a burn running alongthe bottom of the gulley. Provides good potential habitat fornesting merlin but no signs seen.

10 NN 62956 79016 S of North Drumochter Lodge DrumochterPlucking post found with fresh blood.

11 NN 62890 78156Area between NorthDrumochter Lodge and mobilephone mast.

Drumochter

Fairly homogeneous stands of heather moorland managed bymuir burn. Heath height mainly 30-45cm in unburnt areas andtherefore suboptimal for nesting merlin. Numerous small burnswithin heather.

12 NN 62737 78044Burn to N of Creagan DoireDhonaich (S of NorthDrumochter Lodge)

DrumochterDry gulley with fairly deep heather on both sides providingpotential habitat for merlin. No merlin signs.

13 NN 63558 76423 Gulley between Waterfallsand Creagan Doire Dhonaich DrumochterGulley with deep heather growing on either side providing good,

sheltered and undisturbed merlin habitat. No merlin signs.

14 NN 63604 75636 Waterfalls (Allt a' Chaorainn)just N of Creag nan Ubhal Drumochter

Steep sided, sheltered gully with deep heather on either sideand fairly fast flowing burn at base opeing to a small waterfall atthe base of the hill. A merlin was sighted flying up the burn butno signs were found of a nest. This route is used by walkers toaccess the mountains summit (three groups encountered duringsurvey) and beyond so disturbance may be reasonably highduring the spring and summer.

15 NN 64391 74419 Moorland to N of DalnaspidalLodge DrumochterDry heather moorland

16 NN 64854 74009 Burn to N of DalnaspidalLodge Drumochter

Rocky and steep gorge with trees in sheltered positions. Somebracken stands. Heather grazed and shallow, suboptimal formerlin.

17 NN 64365 73559 Plantation just north ofDalnaspidal Lodge DrumochterConifer plantation with no located crow nests. No merlin signs

18 NN 64060 73327 Wetlands to W/NW ofDalnaspidal Lodge DrumochterFlooded wetland with grassy islands.

19 NN 63100 73200 Plantation strip by road to thesouth of the county boundary Drumochter Immature conifer plantation (10-15yrs), no crow nests located,

no merlin signs.


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Table 22.49: Merlin flights recorded in the Drumochter Hills SPA study corridor

Flight Date Weatherconditions

Time SPA Location Flighttimeand

height

Details

1 12/05/04 Cloud cover20%, windspeed 2,southerlydirection,sunny andwarm, 18°C

13.35 No Just south ofDalwhinnie

15secsat <5m

Merlin flew along river bankand into heather on side ofbank furthest from road.

2 12/05/04 As above 14.45 No Just south ofDalwhinnie

15secsat <5m

Perched on fence post andthen flew down into heatheron far side of railway line.

3 25/05/04 Cloud cover30-40%,wind speed2,northwesterlydirection.

15.15 Yes DrumochterPass

15secs at<5m,15secs at5-60m.

Flew north parallel to road,then climbed to 5-60m andflew under transmissionline, over the top of theplantation and alongmountainside out of sight.

4 23/07/04 No weatherdetails asrecordedduring BBS

Nodetails

No Trinafour 30secs at<5m

Noted flying over moorlandduring breeding birdsurvey.

Results of SNH 2004 Survey

22.11.8.6 The following is a summary of the SNH commissioned merlin survey completed in 2004 (Cooper &Gallacher 2004). The main area of heather dominated habitat within the SPA lies on either side ofthe central glen known as the Drumochter Pass, which includes the transmission line route.Elsewhere within the SPA suitable habitat was found on the western periphery of the site alongLoch Ericht and in the Cama’ Choire area towards the eastern boundary.

22.11.8.7 The survey detected the presence of merlin in four locations within the SPA (Figure 22.17, DeskStudy Record Nos. 612 to 618 in Section 22.2 of the Confidential Annex), with birds at two ofthese locations providing evidence of territorial behaviour or potential breeding:

22.11.8.8 To the west of the proposed 400kV overhead transmission line route there were four sightings of amale and two sightings of a female (Desk Study Record Nos. 615 to 617 in Section 22.2 of theConfidential Annex) between April and July, with birds moving between two locations along theglen (within 1.3km of the proposed transmission line route at the most easterly of these twopoints). Although territorial behaviour was displayed on several occasions and breedingsuspected, no nest site was located.

22.11.8.9 To the east of the proposed 400kV transmission line, a merlin was heard alarm calling below therim of the crag in May within 100m of the proposed transmission line route but no bird was sighted(Desk Study Record No. 612 in Section 22.2 of the Confidential Annex). Prey remains were foundnearby. There were no further signs of presence on subsequent visits to the area.

22.11.8.10 A pair of merlin was disturbed in birchwoods on the banks of Loch Ericht, 6.25km west of theproposed 400kV transmission line route, in May and again in July (Desk Study Record No. 613 inSection 22.2 of the Confidential Annex). To avoid further disturbance these sightings were not


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investigated until August, when a pair were again seen both at and around the suspected nest site(Desk Study Record No. 614 in Section 22.2 of the Confidential Annex). However, no nest sitewas confirmed and no juveniles were seen.

22.11.8.11 Approximately 1.5km east of the proposed transmission line route, a male was flushed from theburn and flew up the hillside and outwith the SPA (Desk Study Record No. 618 in Section 22.2 ofthe Confidential Annex). However, there were no further signs of presence on subsequent visits tothe area.

22.11.9 Evaluation of Drumochter Hills SPA Study Site for Merlin

22.11.9.1 There were no confirmed merlin nest sites within 1km of the proposed 400kV overheadtransmission line route. Desk study records indicated a probable territory within grid square NGRNN 67 during 2004 but more detailed observations by SNH surveyors observed movement of aprobable breeding pair of merlin between NGR NN 57 and NGR NN 67, although no actual nestsite was located. The most easterly point of this movement corridor was more than a kilometredistant from the proposed transmission line, although the bird seen flying up Allt a’Chaorainn(NGR NN 63604 75636) during HEL surveys of the route corridor may have been an individualfrom the same pair. Furthermore, merlin activity throughout the study site was low in frequency,with limited flightlines (n=9) and alarm calls (n=2) being recorded around the area of theDrumochter Pass. Given the intensity of combined survey effort (of approximately 375 hours), theuse of the study corridor (containing both the existing 132kV and proposed 400kV line) andsurrounding area by breeding/foraging merlin is considered to be low.

22.11.10 Potential Impacts

22.11.10.1 Potential impacts resulting from the proposed project within the Drumochter Hills SPA include:

• The construction of new infrastructure, including excavation of borrow pits, tower bases &foundations, stringing of lines, site compounds and access tracks (including upgrades toexisting tracks), clear fell of plantation and woodland areas, construction of temporary lay-down areas and site office(s);

• Post construction (operational) activities, including routine line and overhead corridormaintenance works, and the potential need for emergency works; and

• Dismantling of the existing 132kV and proposed 400kV lines, including the removal ofredundant infrastructure, access to working areas, destringing / dismantling of towers andassociated foundations, construction of new access tracks (temporary & permanent) andupgrades to existing roads, construction of temporary laying down area and temporary siteoffice(s).

22.11.10.2 It is considered that these activities could potentially result in the following potential direct andindirect impacts upon merlin within the Drumochter Hills SPA:

Construction Phase

• Disturbance due to increased human activity and vehicular access; and• Habitat loss/displacement and/or damage.

Operational Phase

• Indirect and direct habitat loss / damage and indirect barrier effects;• Management of overhead corridor, resulting in habitat damage/loss and /or disturbance;• Disturbance due to increased human activity and vehicular access;


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• Potential bird collisions with wires (conductors and earth wires) and/or towers; and• Potential electrocution.

Dismantling Phase (132kV and 400kV transmission lines)

• Disturbance due to increased human activity and vehicular access;• Habitat loss and/or damage;• Habitat gain as a result of removal of redundant transmission line structures; and• Reduction in potential collision risks with towers and conductor/earth wires.

22.11.11 Specific Mitigation Measures

22.11.11.1 The following agreed mitigation measures are specific to the Drummochter Hills SPA and includeall those mitigation measures which are relevant to merlin and the SPA.

Construction Phase

22.11.11.2 The framework outlined in the access strategy set out in Appendix D would be used to define theaccess protocol for constructing the 400kV overhead transmission line. No permanent accesstracks would be constructed within the sensitive ecological area defined as the Drumochter HillsSPA, and all temporary tracks used for construction of the new overhead transmission line wouldbe fully restored. Existing access tracks would be used wherever possible to transport equipmentand materials to tower construction locations. New accesses would be routed where possiblethrough land of low ecological sensitivity, defined as Low Local or Negligible Value in theecological assessment;

22.11.11.3 No site compounds would be located within the Drumochter Hills SPA;

22.11.11.4 Borrow pits would not be located within the Drumochter Hills SPA;

22.11.11.5 A SHETL environmental representative would attend site during the construction period whowould be supported by appropriate ecological advisors as required. The representative wouldensure that all environmental mitigation measures set out in this Special Study, the ES, theConstruction Procedures Handbook and any subsequent consent related commitments weredelivered and that the contractor’s own Environmental Management System was successfullyimplemented.

22.11.11.6 The working corridor and storage areas would be kept to the minimum necessary for safeimplementation of the works and the site boundary clearly marked with appropriate methods in allareas identified in the Construction Procedures Handbook as necessary to protect ecological orother interests to prevent incursion outwith the corridor. All such areas would be fully restored atthe end of construction.

22.11.11.7 Exclusion zones within the work corridor would be clearly delineated on the ground to avoidconstruction staff straying into sensitive areas.

22.11.11.8 Restoration plans for all sites of ecological value would be included within the ConstructionProcedures Handbook

22.11.11.9 A breeding bird survey would be carried out, by suitably experienced ecologists/ornithologists atan appropriate time of year and using methods discussed with SNH to inform the micrositing ofaccess tracks and towers. The detailed locations of access tracks and towers would be identifiedin the Construction Procedures Handbook. (see Chapter 13).

22.11.11.10 Should any nesting merlin be identified in the pre-construction surveys or after construction hasbegun, an appropriate buffer zone between the nest site and development corridor would beidentified by the SHETL environmental representative and maintained until the birds have left thenest. A buffer zone of 500m from merlin nest sites is recommended within best practice forestry


Page 22.11 - 14

working guidelines (Currie 1997), although this distance is a guide and would be finallydetermined by appropriate ecological advisors in consultation with SNH on a site by site basis(e.g. dependent on site topography, etc.)

22.11.11.11 Along the overhead transmission line, no construction (including bridge works and existingsubstation building alteration) would take place during the breeding bird season (April to Julyinclusive) apart from where it has been possible to discourage birds nesting (for example by pre-felling of woodland, use of fencing, ticker tape marking of areas, the use of posts, flapping tapeand possibly netting) and/or where pre-construction surveys have indicated that no birds arenesting. Should any nesting birds be identified in the pre-construction surveys or afterconstruction has begun the nest site would be fenced off and an appropriate buffer zone (thiswould be species dependent) identified by the SHETL environmental representative andmaintained until the birds have left the nest.

22.11.11.12 Construction work carried out during the bird breeding season would also ensure that Schedule 1and Annex 1 species (i.e. those with enhanced statutory protection) are appropriately considered.As a guide figure 500m would be used as the limit of likely disturbance and this would beimplemented according to the specifics of the particular topography and site conditionsencountered. Access track construction, tower erection and/or stringing would be assessed on thisbasis in areas where these bird species are breeding. Travel along access tracks during thebreeding bird season would also be minimised (e.g. by stockpiling of materials outwith sensitiveperiods). The exact number of transits would be determined according to the particularsensitivities, topography, etc. found in specific locations. These limits of disturbance and transitswould be determined by the SHETL environmental representative (with additional ecologicalexpertise, as required), to ensure that no significant disturbance occurs to Schedule 1 and Annex1 species.

22.11.11.13 All site staff would be briefed on procedures which would be implemented if any nesting merlin arefound within the construction area. Work would stop in the area until specialist advice is soughtand implemented.

22.11.11.14 Stringing the line with helicopters would be completed where possible. This would consist of ahelicopter working for a maximum of one day in one local area to achieve this. Such disturbance,although extremely temporary, would be assessed on an area by area basis taking account ofSchedule 1/Annex 1 species, should it be necessary within the breeding bird season of April toJuly inclusive

Operational Phase

Routine Maintenance

22.11.11.15 Routine maintenance proposals within the Drumochter Hills SPA would be subject to consultationwith SNH.

22.11.11.16 Routine maintenance would be undertaken with due regard to the protection of important andsensitive habitats, and best practice adopted that minimises environmental impact. A documentwould prepared outlining the routine maintenance procedures;

22.11.11.17 Maintenance Plans would be produced to ensure habitat management within the working corridoris undertaken in accordance with appropriate best practice.

22.11.11.18 Significant maintenance activities which have the potential to cause disturbance to breedingmerlin would not be undertaken within the bird breeding season (April to July inclusive), apart fromwhere this could compromise security of supply or safety.

22.11.11.19 All site staff would be briefed on procedures which would be implemented if any nesting merlin arefound within the maintenance or other work areas. Work would stop until specialist advice issought and implemented. For example, if maintenance was required to a pylon within 500m of a


Page 22.11 - 15

merlin nest, this work would be carried out following liaison with SNH and under the guidance ofan ecological advisor.

Emergency Works

22.11.11.20 Emergency maintenance would be carried out with due regard to the protection of the DrumochterHills SPA, and for disturbance to its qualifying protected species. This would be ensured throughthe preparation of an emergency works environmental action plan to ensure minimalenvironmental impacts.

Dismantling Phase - 132kv Line

22.11.11.21 The framework outlined in the access strategy set out in Appendix D would be used to define theaccess protocol for dismantling the 132kV overhead transmission line. No permanent accesstracks would be constructed within the Drumochter Hills SPA and all temporary tracks used forconstruction of the new overhead transmission line and dismantling of the existing 132kV linewould be fully restored. Existing access tracks would be used wherever possible to transportequipment and materials to tower construction locations. New access would be routed wherepossible through land of low ecological sensitivity, defined as Low Local or Negligible Value in theecological assessment.

22.11.11.22 In all areas of the Drumochter Hills SPA where there are no existing access tracks, low groundpressure plant would be used where possible to access tower locations and areas between towers(see Access Strategy in Appendix D).

22.11.11.23 The SHETL environmental representative on site in liaison with the ecological advisor wouldensure that due regard is given to the statutory protection of breeding merlin under the Wildlifeand Countryside Act 1981.

22.11.11.24 Should any nesting merlin be identified in the pre-construction surveys or after construction hasbegun an appropriate buffer zone between the nest and the development corridor would beidentified by the SHETL environmental representative and maintained until the birds have left thenest. A buffer zone of 500m from merlin nest sites is recommended within best practice forestryworking guidelines (Currie 1997), although this distance is a guide and would be finallydetermined by the project ecologist in consultation with SNH on a site by site basis (e.g.dependent on site topography, etc.):

22.11.11.25 All site staff would be briefed on procedures, which would be implemented if any nesting merlinwere found within the working area. Work would stop in the area until specialist advice is soughtand implemented.

Dismantling Phase - 400kV Line

22.11.11.26 A full assessment of the impacts of dismantling on the ecological resource of the 400kVtransmission overhead transmission line corridor would be undertaken prior to dismantling theline. Mitigation measures are likely to include measures which are similar to those defined fordismantling of the 132kV overhead transmission line and a commitment to implementation of bestpractice environmental measures on site as appropriate for particular locations and time periods.

22.11.12 Assessment of Impact of Mitigated Project

22.11.12.1 The following provides an assessment of post mitigation impacts on the Drummochter Hills SPA,according to the various phases of the proposed project.


Page 22.11 - 16

Construction Impacts

Disturbance Due to Increased Human Activity and Vehicular Access

22.11.12.2 The construction of the proposed overhead transmission line has the potential to result inincreased temporary disturbance to breeding and hunting merlin during construction of the line,due to the general increase in human activity and plant in areas of the Pass where disturbancelevels are relatively low and possibly habituated to current disturbance (i.e. from passing vehicleson the A9 trunk road). No evidence of breeding merlin was confirmed within 1km of the proposedtransmission, and therefore there would be negligible disturbance to breeding merlin. Merlinactivity within the construction corridor was very low.

22.11.12.3 Given that merlin move to lower ground away from the hills during winter, it is thereforeconsidered that there would not be a significant impact to either breeding or wintering merlinduring the construction phase.

• Impact Magnitude: Negligible• Impact Significance: Negligible

Habitat Loss and/or Damage

22.11.12.4 Habitat loss/and or damage would result from the construction of access tracks and towers andfrom felling of trees where access tracks pass through existing plantation woodland. Designmitigation measures have ensured that habitat loss, damage and disturbance would be minimisedby using only temporary access tracks which would be subject to full restoration, and by upgradingexisting tracks where possible and siting new temporary tracks to avoid the need for any treefelling. Micrositing of towers would be undertaken to avoid disturbance or damage to areas ofpotential breeding merlin habitat.

22.11.12.5 No evidence of breeding merlin was confirmed within 1km of the proposed transmission, andtherefore there would be no loss and/or damage to breeding habitat.

22.11.12.6 The extent of heather-dominated moorland that would be lost or damaged is considered torepresent a negligible loss of hunting habitat for birds in relation to the area of available habitat.Furthermore, this habitat loss would be offset by the moorland habitat that would becomeavailable when the 132kV overhead transmission line was dismantled. The activity level of merlinwithin the transmission line corridor is low, indicating that this is not a critical element of a homerange.

22.11.12.7 No crow nests were located which could potentially be used as alternative nesting areas for merlinwithin the construction corridor. Furthermore, no tree felling would be required during theconstruction or upgrading of access tracks.

22.11.12.8 The negligible amount of habitat lost around the footprint of each tower would have minimalimpact for merlin because the majority of ground over which the proposed route would beconstructed is of low value for merlin. Micrositing of towers during construction would ensure thatno suitable areas (comprised of sheltered burns or gullies with deep heather to provide potentialcover for nesting) would be directly affected.

• Impact Magnitude: Negligible• Impact Significance: Minor

Operational Impacts


22.11.12.9 Some disturbance may be caused during routine maintenance or emergency works due toincreased human activity and vehicular access. However, mitigation commitment confirms that nosignificant maintenance activities which have the potential to cause disturbance to breeding birds


Page 22.11 - 17

would be undertaken within the bird breeding season (April to July inclusive), apart from wherethis could compromise security of supply or safety. Emergency maintenance work would becarried out with due regard for disturbance to protected species, particulalry merlin.

• Impact Magnitude: Negligible• Impact Significance: Minor

Direct and Indirect Habitat Loss and Barrier Effects

22.11.12.10 It is predicted that there would be very little additional direct habitat loss or damage during theoperational phase, e.g. due to routine maintenance or emergency works. However, some small-scale loss/damage may result, especially if construction of temporary access tracks were required.

22.11.12.11 Although merlin nests can be predated by crows (Rebecca & Cosnette 2003), no nests werelocated or territories confirmed within 1km of the proposed or existing routes. Coupled with the lowcorvid population in the area, merlin nests within the SPA are therefore unlikely to be the subjectof increased arial or terrestrial predation as a result of the new transmission line.

22.11.12.12 Barrier effects could potentially result from the presence of the overhead transmission linepreventing merlin from using the surrounding area. However, although at a low level, the areasurrounding the existing 132kV transmission line is currently used by feeding merlin (albeit at lowlevels). It is likely that merlin will habituate to the proposed line in a similar way. Furthermore, thetowers of the new transmission line may serve as perching posts for merlin, thereby aiding thelocation of prey.

• Impact Magnitude: Negligible• Impact Significance: None

Displacement of Prey

22.11.12.13 No significant change in density of meadow pipits was found in the vicinity of the existing 132kVoverhead transmission line, when compared with density on adjacent open ground. However, it ispossible that the habitat of ground-nesting birds could become less favourable as a result of thepresence of towers and associated wires displacing birds of open ground, and due to increasedaerial predation due to the towers and line wire providing increased perching opportunities forpredators.

22.11.12.14 The moorland and woodland habitat within the SPA is fairly homogeneous and it is likely that, ifdisplacement were to occur, prey species such as meadow pipits would merely relocate to anadjacent area of similar habitat. Given the range over which merlin forage, it is considered thatthe area of habitat from which merlin prey species could potentially be displaced represents anegligible loss of feeding resource for merlin in relation to the area of available habitat within theSPA and surrounding areas. Moreover, the removal of the existing 132kV overhead transmissionline will negate this overall effect.

• Impact Magnitude Negligible• Impact Significance None

Collision Mortality

22.11.12.15 Bird mortality due to collision is considered potentially to represent the most important impact ofpower lines on birds. For a review of risk factors of collision mortality with power lines for differentbird groups, refer to Section 22.22. Although raptors often occur within the potential collision riskband of power lines, they are highly manoeuvrable with generally low wing loading. However, it isimportant to consider potential impacts of the proposed 400kV overhead transmission line onvulnerable, dispersed populations of raptors such as the merlin population within the DrumochterHills SPA.

22.11.12.16 Very simply birds can collide with power lines because they can be difficult to see, although thedegree of risk depends on a number of factors. These relate both to the species and their


Page 22.11 - 18

behaviour, environmental factors and type and design of the power lines themselves. In mostcases the physical impact of collision leads to immediate death or to fatal injuries and mutilation,although some birds may recover. The majority of bird collisions appear to be associated withearth wires, normally installed above the conductors, and less visible than the conductors (whichare of a greater diameter and can also be bundled, further increasing their visibility) (e.g. Scott etal. 1972). Therefore, birds seem to be generally capable of recognising the supporting towers andconductors, but the earth wire can in certain situations appear almost invisible because ofbackground or lighting conditions, and bird collisions result (APLIC 1994). Also important is thatbirds may take avoiding action from the towers and conductors by increasing flight height,resulting in collision with the earth wire.

22.11.12.17 In order to estimate the risk of collision with the proposed transmission line for merlin using theSPA a collision model has been used (see below).

22.11.12.18 From 144 hours of survey, 4 merlin flights were recorded. In order to calculate the level of annualactivity that the above flights represent it is necessary to calculate the number of hours in thebreeding season over which birds could potentially be active. This has been done using publishedsunrise and sunset times for April to August (representing the occupancy period) in order toestimate the total number of hours for each month (see Table 22.50).

Table 22.50: Estimate of merlin annual occupancy within Drumochter Hills SPA

Month HoursApril 431.5May 514.7June 534.5July 531.5August 468.3Total 2,480.5

22.11.12.19 This will probably over-estimate the actual number of hours of activity as the combined period ofincubation and chick rearing to fledging is, on average 59 days with young being indpendentaround one month later. However, the extra days included in the above calculation will cover atypical period from arrival of the parents at the nest site to the departure of the young, followingtheir period of post-fledging occupancy in the vicinity of the nest site.

22.11.12.20 Since no flights were recorded during April and watches were not carried out in August, the flightdata from these months will not be used in calculating the annual activity levels as it is consideredthis would give too low an estimate. The fact that no birds were recorded in April suggests thatbirds did not arrive and start to nest until May. However, in future years nesting may well beginearlier, meaning April should not be discounted from the calculation of the maximum number ofpotential hours of annual activity.

22.11.12.21 Of the 4 flights recorded in May to July, only one crossed the overhead transmission line (also atcollision height). So, one flight in total crossed the line at collision height from 108hrs of watcheswhich equates to 0.009 per hour.

22.11.12.22 Assuming 2,480.5 hours of potential activity per annum as proposed above, this gives 22 flightscrossing the overhead transmission line at collision height per year.

22.11.12.23 Following the procedure set out in the collision model methodology (see Section 22.2.4) and using0.62m as the maximum wingspan of a merlin (Cramp 1980) the theoretical collision rate can becalculated as 6.2%.


Page 22.11 - 19

Table 22.51: Merlin collision model summary for Drumochter Hills SPA

Theoretical ModelEmpirical Modelmean n flights/h 0.009 0.009 n/hpotential active period 2480.5 2480.5 hnumber flights/pa 22 22 flights/pacollision rate 6.2 0.017 %MERLIN COLLISIONS pa1.36 0.004 strikes/year

22.11.12.24 Using the theoretical avoidance rate from the trigonometric model (MBEC 2005) this wouldestimate 1.36 flights colliding per year. However this takes no account of avoidance behaviour andit is considered that for a small manoeuvrable raptor such as a merlin a more appropriate estimateof collision rate would be to use collision rate figures as published in the literature. No studiesdealing specifically with merlin were found but the following paper gives some useful figures.Alonso & Alonso (1999) produced estimates of collision rates for numerous species on overheadtransmission lines of various design (between 220kV and 380kV) in several study areas in Spain.This study looked at both flight frequency and estimated an annual collision rate from carcasssearches beneath the lines. Although they did not record merlin during this study they did giverates for kestrel (Falco tinnunculus), a raptor of similar size and wingspan, within two differentstudy areas. Although comparable in size, kestrel hunt for insects and small mammals using agliding/hovering and aerial attack technique, whereas merlin tend to pursue passerines by flyinglow and fast over the ground and perching on lookout posts, often mimicking a mistle thrush-typeflight whilst in pursuit.

22.11.12.25 Although Alonso & Alonso did not record mistle thrush, they do give a figure for song thrushcollision rate. It is considered that the collision rates recorded for these species represents arange in which merlin would fall. An average of the rates for these species gives a collision rateof 0.017% of flights. Alonso & Alonso calculated this rate from all flights crossing the transmissionlines regardless of height. Using this rate with the flight frequency calculated above (22 flights)equates to 0.004 merlin collisions per annum or one collision in 250 years. This is effectively0.03% of the Drummochter Hills SPA population (cited as 7 pairs in the SPA citation).

22.11.12.26 The figure used for the collision rate should be treated as a minimum collision rate as the authorsstate that the methods used to arrive at annual collision estimates are prone to error due to anumber of factors that have to be corrected for (such as removal of carcasses under the lines byscavengers and carcasses going undetected due to the nature of the terrain and vegetation). Thismeans that it is virtually impossible to arrive at accurate mortality figures (a problem identified inmany studies) although this is less pronounced for larger species (i.e. bigger than a mallard) thansmaller birds. However, even if the actual collision rate was ten times that predicted using theabove figure this would still represent a mortality of far less than 1% of the SPA population perannum or one bird every 83 years.

22.11.12.27 It should also be noted that the current baseline conditions include an existing 132kV overheadtransmission line that would be dismantled as part of this project. The impact of collision istherefore only the difference in risk between the existing line and the proposed line. The abovemodel does not take this into account but if it did, the predicted rate of collision in comparison tobaseline conditions would be significantly less than the above rate.

22.11.12.28 Collision with high wires was considered one of the main causes of injury to merlin in England byBrown in a 1976 study. A 1989 BTO research report used mortality data from ringed birds(between 1909 and 1987) to assess the effects of collision with overhead power lines. A ‘hit wireindex’ (HWI) was calculated based on the proportion of ringed birds found dead against thenumber that had a recorded cause of death as ‘hit wire’. Of a total of 87 species included in theanalysis, merlin were included as one of 7 species with a HWI of greater than 10. However, of the5 ‘hit wire’ recoveries in Scotland, 80% were coastal. Although dead birds were found throughoutthe Highlands, none of these were recoveries of ringed birds which had hit wires. Furthermore, the


Page 22.11 - 20

analysis was based on data gathered from both transmission and distribution power lines: thelatter type are lower and much less visible to birds in design. The design of the proposed linewould involve bundled conductors between conductors and an earth wire of a much greaterdiameter than that used as a component part of lower voltage power lines (including 132kVtransmission lines such as those found throughout the Scottish Highlands).

22.11.12.29 The species is known to be extremely manoeuvrable in flight. For example, a merlin was observedchasing a meadow pipit around and between the conductors of the existing 132kV line to the northof the SPA at Glen Truim (Andy Mackenzie, pers. com. 2004). The thicker earth wire and bundledconductors of the proposed design would make the structure more visible to birds than similarcomponents of the existing 132kV transmission line. Given that an overhead transmission line isalready in place within the SPA, it is considered that the inherent design features of the proposedtransmission line (which runs almost in parallel with the existing line), would provide animprovement or positive impact upon current baseline conditions in terms of collision mortality riskfor merlin.

22.11.12.30 However, given a cautious approach it has been assessed that the impact of merlin collisionwould be negligible with no perceptible effect on population viability and therefore the integrity ofthe SPA.


Electrocution of Merlin

22.11.12.31 For a full overview of risk factors of electrocution by power lines for different bird groups, refer toSection 22.6 in the Ecology and Nature Conservation chapter. Electrocution occurs whenever abird touches two phase conductors, or conductor and earth wire (Bevanger 1994) and can be aparticular problem for power lines with a voltage of under 130kV (i.e. low voltage power lines) dueto their inherent designs.

22.11.12.32 Risk factors for electrocution can be split into two areas: flight and nesting behaviour. Large size isby far the most crucial factor that makes certain raptors, e.g. eagles, susceptible to electrocution.Both critical distances (phase-to-phase and phase-to-earth) are greater in the proposed 400kVdesign than in the between phase and phase-to-earth distances of the existing design. Thereforeits inherent design means that the distance of phase-to-phase and closest phase-to-earth contactis significantly greater than the wing span of even golden eagle, the raptor with the largest wingspan found in the geographic area of the transmission line. Both these critical distances are alsomuch greater than the effective increased wingspan of two golden eagles joined during display orby talon linking during territorial defence. The relatively small merlin wingspan therefore rules outthe possibility of electrocution by phase-to-phase or phase-to-earth contact.

22.11.12.33 Merlin are ground/tree (typically in old nests of crows) nesting and have not knowingly beenrecorded nesting on transmission lines, thereby removing the potential risk factors associated withtransmission line nest sites.

22.11.12.34 Merlin may use the proposed overhead transmission line for perching whilst resting and foragingfor prey, although this behaviour has not been recorded during either the 2004 HEL or SNHsurveys. Electrocution could potentially occur in this situation if a defecating bird allowed a phase-to-phase or phase to earth contact. However, the very low degree of risk involved under thisscenario is considered to be the same for both the existing 132kV transmission line and theproposed 400kV transmission line, and is outweighed by any potential benefit that may beprovided by birds perching on the line to locate prey.

• Impact magnitude: Negligible• Impact significance: None


Page 22.11 - 21

Dismantling Impacts - 132kV Line


22.11.12.35 The dismantling of the 132kV overhead transmission line has the potential to result in increasedtemporary disturbance to breeding and hunting merlin, due to the general increase in human andvehicular activity in areas of the Pass where disturbance levels are currently relatively low andbirds are possibly habituated to current disturbance (i.e. from passing vehicles on the A9 trunkroad). However, no evidence of breeding merlin was confirmed within 1km of the existing 132kVline. Therefore there would be negligible disturbance to breeding birds. Given that merlin move tolower ground away from the hills during winter, there would be negligible disturbance to eitherbreeding or wintering merlin during the dismantling phase.


Merlin Habitat Loss and/or Damage

22.11.12.36 Dismantling of the existing 132kV overhead transmission line has the potential to result in habitatloss and/or damage of merlin habitat compared with the current baseline situation due to the needfor access to and between towers, and the removal of towers and their foundations. All accesstracks used in the dismantling process within the SPA would be temporary and subject torestoration. Where possible low ground pressure plants would be used in the dismantling works,negating the requirment for construction of access tracks.

22.11.12.37 The area of potentially suitable heather moorland that would be damaged during dismantling isconsidered to represent a negligible, temporary loss of breeding/feeding habitat for merlin, inrelation to the area of available habitat. It is considered that this would have minimal impactbecause the majority of ground over which the existing 132kV transmission line is routed is of lowvalue for merlin, with potentially suitable nesting areas being unaffected by the presence ordismantling of the existing transmission line.

22.11.12.38 No crow nests were located which could potentially be used as alternative nesting areas for merlinwithin the dismantling corridor. Furthermore, only limited areas of coniferous trees would be felledas a result of the dismantling work.

• Impact magnitude: Negligible• Impact significance: Minor

Habitat Gain Resulting from Removal of Existing Line Structures

22.11.12.39 With the exception of the area around North Drumochter Lodge, the majority of the existing 132kVoverhead transmission line follows the route of the A9 road and lies to the road side of theproposed 400kV overhead transmission line. Due to its proximity to the A9 road and deerbrowsing and trampling, any habitat gained as a result of removing the existing 132kV line is likelyto be of low quality and therefore of low value for merlin. Merlin do not use the existingtransmission line for nesting. Merlin may perch on the existing line whilst searching for prey,although this behaviour has not been observed during this study.

• Impact magnitude: None• Impact significance: None

Removal of Potential Collision Risk with Towers and Conductors

22.11.12.40 Any potential positive impacts (in terms of reduced potential collision risk) of dismantling theexisting 132kV overhead transmission line are likely to be counterbalanced by construction of thenew 400kV overhead transmission line resulting in similar conditions to the current baseline.However, collision risk (and electrocution risk) with overhead transmission lines is not consideredhere to be a significant mortality factor for merlin.


.11 - 22

• Impact magnitude: None• Impact significance: None

Dismantling Impacts - 400kV Line

22.11.12.41 Future dismantling of the 400kV overhead transmission line has the potential to negatively impacton merlin, both directly and indirectly. Due to the anticipated passage of time betweenconstruction of the 400kV transmission line and dismantling (c.80 years), a pre-dismantling surveywould be required during the breeding season prior to the start of dismantling works, in order toprovide an up-to-date assessment of the population. It is therefore not possible to assess thepotential impacts of dismantling. The scale and therefore significance of potential impacts uponthe merlin population within the SPA will depend upon the status and distribution of the populationand habitat quality within the SPA at the time of dismantling of the 400kV overhead transmissionline, and the work timing and methods proposed. However, the nature of potential impacts andmitigation measures are likely to be similar to those involved in dismantling of the 132kV overheadtransmission line, and any predicted significant impacts are likely to be mitigated by definingworking practices and timing of works.

22.11.13 Summary

22.11.13.1 Merlin were surveyed using a variety of intensive survey methods during April to August 2004,both along a 1km corridor of the proposed route and throughout the wider SPA area. Desk studyrecords were also collated from various consultees. Findings from the study indicate very low useof the route corridor and surrounding area by hunting merlin. There were no confirmed orsuspected merlin nest sites within 1km of the proposed 400kV overhead transmission line route.The proposed project is assessed to have low impact and minor significance overall for the current(2004) merlin population within the Drumochter Hills SPA (see Table 22.52).

22.11.13.2 Given the level of merlin activity during 2004 (and distance of suspected nesting activity from theproposed transmission line), along with the level of committed mitigation by SHETL, it isconsidered that no phase of the project would significantly impact upon merlin in terms ofpopulation size or distribution. Nor is the proposed project predicted to have significant impactsupon the distribution, extent, structure, function or supporting processes of the habitats supportingthe qualifying bird species within the SPA as examined within this special study. It is consideredthat the qualifying species would not be significantly disturbed by any phase of the project.

22.11.13.3 It has been shown in this assessment that the proposed project would not affect any of theConservation Objectives of the Drumochter Hills SPA, and there would be no adverse impact onthe integrity of the SPA.

22.11.13.4 However, it is important to note that the merlin population size and distribution within the SPA maychange over time. Pre-construction surveys would therefore take place prior to each phase(construction of the 400kV line, and dismantling of the 132kV line and the 400kV line in the future)and appropriate mitigation measures put in place in order to ensure non-significant impacts on theSPA’s merlin population.


Page 22.11 - 23

Table 22.52: Summary Assessment of the Mitigated Project upon Drumochter Hills SPAPotential Impact Potential Magnitude Potential SignificanceConstruction PhaseDisturbance due to increasedhuman activity and vehicularaccess

Negligible Negligible

Merlin habitat loss and/or damage Negligible MinorOperational PhaseDisturbance due to increasedhuman activity and vehicularaccess

Negligible Minor

Direct and indirect habitat loss andbarrier effects

Negligible None

Displacement of prey Negligible NoneCollision mortality Negligible NegligibleElectrocution of merlin Negligible NoneDismantling Phase - 132kV LineDisturbance due to increasedhuman activity and vehicularaccess

Negligible Negligible

Merlin habitat loss and/or damage Negligible MinorHabitat gain resulting from removalof existing line structures

None None

Removal of collision risk withtowers and conductors

None None

Dismantling Phase - 400kV Line To be assessed at time of dismantling – likely to besimilar to those assessed above for the 132kV line

Overall Assessed Impact Negligible Minor

22.11.14 References

• Becker, D.M., Sieg C.H. 1987. Home range and utilisation of breeding male merlins, Falcocolumbarius, in southeastern Montana, Canadian Field-Naturalist, 101: 398-403.

• Bibby, C.J. 1986. Merlins in Wales: site occupancy and breeding in relation to vegetation,Journal of Applied Ecology, 23: 1-12.

• Bibby, C.J., Nattrass M. 1986. Breeding status of the merlin in Britain. British Birds 79: 170-185.

• Bibby, C.J. 1987. Foods of breeding Merlins Falco columbarius in Wales. Bird Study, 34: 64-70.

• Brown, A.F., & Shepherd K.B. 1993. A method for censusing upland breeding waders. BirdStudy 40: 189-195.

• Cooper, B., & Gallacher, J. 2004. Site Condition Monitoring of Aggregation of BreedingMerlin (Falco Columbarius) within the Drumochter Hills SPA/SSSI. A report by Tilhill ForestryLtd. for Scottish Natural Heritage.

• Cramp S., Simmons K.E.L., Gillmor R., Hollom P.A.D., Hudson R., Nicholson E.M., OgilvieM.A., Olney P.J.S., Roselaar K.H., Voous K.H., Wallace D.I.M. & Wattel, J. 1980. Handbookof the Birds of Europe, the Middle East and North Africa: The Birds of the Western Palearctic– Volume 2, Hawks to Bustards.

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