Square bashing:
Breeding bird surveys in the Ochils
Roger Chapman
MOST PEOPLE we meet walking or running in the Ochils seem to be enjoying, more
or less, some leisure activity and exercise. Perhaps the next most common category
is people going about their normal occupation such as working with sheep, forestry
or water engineering. A few people on and about our hills are engaged in other
activities. These include the collection of meteorological records, archaeological
work and wildlife surveys.
In general, bird surveys are managed by the British Trust for Ornithology (BTO),
whose Scottish headquarters is at Stirling University and whose UK HQ is in
Thetford, Norfolk. This work is often carried out in conjunction with other
conservation bodies such as the Royal Society for the Protection of Birds, the
Scottish Wildlife Trust, the Joint Nature Conservation Committee and the Wildfowl
and Wetlands Trust. The BTO is in touch, through a system of regional organisers,
with a large network of UK-wide volunteers (including the writer), on whom it
relies to carry out various surveys, some ongoing, some occasional.
The status of wild birds is an important indicator of the health of the countryside,
and the government has, since 1998, used an annually updated indicator based
on trends in over 100 breeding bird species as one of its “framework indicators”
of progress towards sustainable development. The BTO’s historical records
of breeding and wintering bird species related to districts and habitats provides
impartial, reliable and quantified data that can be consulted whenever developments
might have a significant impact on the local bird life. Also, studies of trends
for particular species and habitats can be important precursors of remedial
conservation work.
Until 1994, the BTO’s most important survey for the purpose of monitoring
trends in breeding bird numbers was the Common Birds Census (CBC), which had
been running since 1962. This was a high-quality but labour-intensive survey
based on farmland and woodland habitats. It did not cover other habitats, and
the survey areas were selected by the volunteers, often giving a bias in favour
of birding hotspots and populous regions which made the derivation of national
statistics problematic. Accordingly, in 1994, a newly designed survey, the Breeding
Bird Survey (BBS), was introduced. This ran in parallel with the CBC until 2000
in order to allow calibration between the schemes before the CBC was dropped.
The key features of the BBS are the random selection of 1km2 areas, UK-wide,
and a less manpower-intensive survey method to encourage wider participation.
In 2005, the latest year for which data are available, 2879 areas were surveyed,
of which 302 were in Scotland and 30 in the Central Scotland region.
The surveyor is asked to walk two 1km transects across the square, the first
north/south (in either direction), the second in the reverse direction - or,
alternatively, east/west and in reverse. The transects are spaced 500 metres
apart and 250 metres from the square edges, and each is divided into five 200-metre
sections. There obviously has to be scope for variation from an ideal line depending
on the nature of the terrain and the access possibilities.
Each square is normally visited three times each year. A preliminary visit codes
the habitat of each 200-metre section of the two transects down to four levels
of detail. This may sound complicated, but in practice it is an exercise that
is carried out once when the surveyor takes on a particular square and rarely
needs to be updated thereafter.
The two main bird counts are then carried out, an “early” count
intended to record the peak numbers of resident species, and a “late”
count to record migrant peaks. (Most subsequent analysis focuses on the higher
number for a particular species, whether recorded early or late.) April to mid-May
is suggested for the early count and mid-May to late June for the late count
in the lowlands of southern Britain, with visits at least four weeks apart.
It is recognised that the visits should be shifted later in the year at higher
altitudes or further north, with the final transect nevertheless being completed
by mid-July. Counts should ideally start between 6am and 7am and no later than
9am; this is because birds generally become quiet and inactive during the middle
of the day. However, start-times can be shifted to begin later in more remote
and less accessible areas.
On each visit, the surveyor walks the two transects (with a gap in between to
move from one to the other) and records the number of birds of each species
seen in each of the 200-metre sections. Each sighting has to be assigned to
one of four distance categories:
1 within 25m either side of the transect line
2 between 25m and 100m either side of the line
3 more than 100m either side of the line, including birds outside the square
boundary
4 birds in flight only (at any distance)
The surveyor is expected to stop from time to time and scan the terrain for
birds. An average visit is expected to last around an hour-and-a-half, in which
case the total fieldwork will be about six hours per year. Nevertheless, much
depends on the location of the square and the terrain. The surveyor does not
have to make a judgement about whether the birds are breeding when seen, merely
to record their presence.
Two BBS squares have been selected in the western part of the Ochils. Both are
at relatively high altitude, with one, NN8601, including Blairdenon summit and
the other, NS8699, including Colsnaur summit. The Blairdenon square was surveyed
in 1994, the pilot year for BBS, but not covered in 1995 or 1996 after the original
surveyor moved away. In 1997 I took over Blairdenon and also took on Colsnaur,
which had not been surveyed before. I have covered both squares continuously
since then, except for 2001 when the foot and mouth outbreak prevented access.
The Blairdenon square encompasses not just the summits of Blairdenon Hill and
Greenforet but also the dip into Glen Tye and across the Old Wharry Burn. The
picture below shows a view of the terrain taken from the summit of Bengengie.
My predecessor set the direction of travel from south to north and then north
to south, so I have kept to that, but have projected 200 metres (rather than
250 metres) in from the west/east borders of the square.
Starting at 545m altitude to the west of Menstrie Moss, the first transect drops
sharply to cross the burn at 495m and then climbs steeply to the summit of Greenforet
at 610m before dropping to 590m on the north side of the ridge.
The second transect begins at 600m on the fenceline to the east of Blairdenon.
After climbing a little to 620m it drops steadily to 530m at the head of the
West Cameron Burn. The steep climbing on the first transect means that it takes
me around an hour to complete it, though the easier second transect usually
takes no more than 40 minutes. Allowing time to walk between them, the whole
survey therefore takes about two hours for each visit - without counting the
walk in and out, of which more anon. When I first considered the often-featureless
survey terrain, I wondered how I would find markers to indicate the various
section boundaries. In practice I soon realised that my altimeter would be the
solution once I’d marked out the square with the boundary contour heights.
The other square includes the Colsnaur and Bengengie ridges, split by the Balquharn
Burn. The picture opposite shows the slopes either side of the glen, with Bengengie
at its head. Since nobody else had surveyed this square, I had free rein to
decide on the direction of the transects. It would have been easiest to go north
on the Colsnaur ridge for the first transect, cross the dip in the upper part
of the glen, and return south on the other ridge for the second transect. However,
I felt that this would not give the best cross-section of the terrain because
it misses out most of the steeply sloping hillsides that make up much of the
square. So I begin the first transect at 525m altitude just west of Colsnaur
summit (near the mossy pool there) and walk east, crossing the ridge wall (545m)
and dropping to the burn (375m) before climbing back up to 500m on the opposite
ridge. The second transect starts near Bengengie (close by the 535m ring contour),
dropping west back down to the burn (crossed at 430m) and up the opposite ridge,
back across the Colsnaur wall (540m) and down again to finish towards the head
of the Second Inchna Burn at 480m. Both transects include a steep climb and
take me about an hour each - allowing time to look for, count and record birds
- so the whole Colsnaur survey takes nearly two-and-a-half hours.
In terms of getting in and out to the two locations, Blairdenon can be most
easily approached from the north via the Sheriffmuir Road, but since the first
transect goes from south to north that would entail an awkward diversion to
avoid disturbing the birds before I start the survey. Colsnaur is easier to
approach from the south, so it gives more flexibility to walk in from Menstrie
whichever survey I’m doing. It is out of the question to cover both surveys
on the same day - but when, in either the “early” or the “late”
season, I still have both squares to do, I sometimes don’t make up my
mind which to tackle first until I get up to around 500m and see what weather
conditions are like.
In order to begin surveying no later than 9am, I aim to set out from Menstrie
soon after 6am. Those who know the Ochils well will appreciate that there can
be low cloud or mist well down the slopes at that hour, but often it lifts later.
There’s no point in waiting low down to see whether it is going to clear,
so I have to accept that sometimes I will have a wasted climb. On these occasions
I usually sit in the depression at Colsnaur summit, perhaps go for a warming
walk north along the ridge once I’ve finished my meal, and head back down
when it becomes too late to start. Usually the Colsnaur square clears before
the rather higher and “further in” Blairdenon square, but on one
or two occasions the reverse has occurred. After finishing Colsnaur, the direct
return route is via the subsidiary ridge between Colsnaur and the Second Inchna
Burn.
After finishing Blairdenon, I either cross Menstrie Moss and return this same
way, or head down the slopes east of the Balquharn Burn to the reservoir and
return to Menstrie along the terrace past Myreton House. It’s usually
close to 1pm by the time I’ve had another snack and got back to the car,
so each survey involves a seven-hour round trip and the year’s fieldwork
takes about five times the notional six hours - even with no abortive trips.
It’s just as well that I enjoy the hillwalking for its own sake.
Anybody walking on the Ochil tops with an eye open for birds will have noticed
that there are not great numbers of them, even in the peak May/June breeding
season, nor is the variety of species high. The relatively lower ground on either
side of the burns is no better than the tops in this respect. Blairdenon (15)
has been slightly more productive than Colsnaur (13) in the variety of species
seen over the years. The presence of a corner of the marshy area of Menstrie
Moss in the former square seems to account for this, giving rise to the occasional
golden plover, red grouse and snipe. Wheatear are seen more often on Colsnaur,
usually near the drystane dyke on the ridge, and a pool in the Balquharn Burn
once (in 2004) boasted a dipper. Otherwise, the two squares have yielded much
the same numbers on average.
By far the highest scoring species are the corvids (mainly rooks and crows),
which often move up the glens in foraging groups from the Forth Valley side.
These are not truly local breeding species any more than the occasional swallows,
martins and swifts which are sometimes seen hawking for insects or in transit
between Strathallan and the Forth. The two next most common, and this time genuine
local breeding birds, are meadow pipits and skylarks. Both these species are
regularly seen in reasonable numbers year by year in both the early and late
season. The yearly maxima have averaged much the same for both squares:
Colsnaur Blairdenon
Meadow pipit 13.0 12.1
Skylark 7.9 8.6
These have been the only two species for which it is possible to detect a clear
trend over the years. Skylark numbers have held up pretty steadily, but there
has been a noticeable decline in the meadow pipit count.
For the rest, the occasional sightings of different species give a little lift
to some surveys, but there is no pattern that I can see. The odd species seen
but not so far mentioned are buzzard, kestrel and red kite (on Blairdenon) and
common gull, curlew, mallard and raven on both squares. I wonder what will turn
up in 2007!