
BIRDS
AS AN INDICATOR OF ENVIRONMENTAL QUALITY
Cóilín
MacLochlainn "Of
all the faunal groups, wild birds are the most useful indicators of environmental
quality - because they are numerous and easy to see; and there are many different
species, all with their own very specific habitat requirements and their own tolerance
limits." |
About
12-15 years ago, agriculture began facing up to the adverse impacts it was having
on the environment. With assistance from Europe, many schemes were introduced
to reduce environmental impacts, most notably the Rural Environment Protection
Scheme. But farming still has a long way to go to avoid further extinctions in
Ireland's native plants and animals. The
other major force in the rural landscape, forestry, is only now beginning to acknowledge
that it can also severely impact on natural habitats and native biodiversity -
though it has been dealing with its visual impact on the scenery for some time. The
Forest Service has invited comments on its review of forestry legislation; Coillte
has issued a short document on sustainable forest management; The national strategy
on forestry aims for at least 10% of new plantings to be broadleaved trees; a
national millennium forest project will focus on the semi-natural broadleaved
resource. The
ranks of foresters are thus lined up on the bank of the Rubicon, about to cross
- though many people say they will need a push to get into the water. The
indomitable Tony Lowes has convened a Coalition for Sustainable Forestry, backed
by all the major conservation NGOs, to provide that push, and it looks as if forestry
may be entering a new era. Certainly,
there is a new awareness and appreciation of broadleaved trees and woodlands,
thanks in part to the campaign by Jan Alexander, who founded the group Crann in
1986. This has
resulted in a slight increase in commercial broadleaved plantings. It has also
encouraged individuals and communities to plant trees, groves and small broadleaved
plantations for aesthetic and amenity purposes, to improve the landscape and the
air, and to do their bit for the conservation of native birds and animals, because,
as we are continually reminded, broadleaved woodlands can be the most species-rich
natural habitat in Ireland. Once
you've established a new broadleaved plantation, or started rehabilitating an
old one, the next logical step is to look at how your woodland management methods
are affecting and benefiting wildlife. If
sustainable forest management is the goal, then we need to look at these things,
but it should be emphasised that it is quite possible to combine commercial timber
production with conservation of fauna and flora in broadleaved plantations - the
models for this can be seen throughout central Europe. Of
all the faunal groups, wild birds are the most useful indicators of environmental
quality - because they are numerous and easy to see; and there are many different
species, all with their own very specific habitat requirements and their own tolerance
limits. Recording
and monitoring the birdlife in a woodland presents certain problems, however,
because the vegetation hides many of the birds present. There
are four basic approaches to a woodland bird survey - and I will use a bird survey
which I carried out in the Oak Glen in Glencree, Co Wicklow, this summer to illustrate
these. The first
is the approach that would have been adopted by natural historians of old, and
is still the way many casual bird surveys are carried out: that is, you simply
visit the site on as many occasions as possible and note everything you see. This
gives you a complete bird list, as well as a list of mammals, butterflies, flowers,
or anything else that the surveyor is able to identify and record. Casual
recording like this, however, does not give you a proper idea of the actual numbers
of the different species present. And you would need more exact information if
you were going to monitor the changes in the bird community as the woodland developed
from scrub to closed canopy. The
second method, then, is mapping, where you spend several weeks mapping out every
single territory held by bird pairs in the plantation. As you can imagine, this
would be exhaustive work. If every bird in the Oak Glen on a midsummer's day could
be captured and then released in this room, it would be like a scene from The
Birds. The room would be filled with thousands of small birds. The terrain in
the Oak Glen is very rough, it has been ploughed up for planting, it is rocky,
there is a lot of brambles and many holes and trenches. It is difficult enough
to walk it, never mind record all the birds using it. Mapping is never more than
70% accurate anyway - you will always miss about 30% of the birds. And mapping
would not be necessary except for research purposes, perhaps in a plantation of
very high conservation value. The
other methods are the transect method and point counts. The
transect method is the easiest. I based a transect count on the method used in
the Countryside Bird Survey, launched by BirdWatch Ireland and Dúchas this
year, which is the same as the tried and trusted method developed by the British
Trust for Ornithology for the British Breeding Bird Survey. Basically,
they survey 1km x 1km squares, chosen at random around the country. Two 1km long
walks, parallel to each other, are carried out in each square. The 1km transect
is divided into five 200m stretches and the birds seen or heard in each individual
200m are noted. Oak Glen is a little smaller than 1x1km, but the same principles
apply. This technique
can easily be carried out in Oak Glen, as there are suitable footpaths one can
follow. You go to the site in April or May, the time of year that the birds are
nesting, and you go at dawn, 7.00am, to catch them in full song, during the dawn
chorus, when they are most easily located and identified, and spend about 2 hours
walking your transects. You do two counts, one in April and one in late May or
June, the second count being carried out to pick up any late migrants that may
have arrived later than April. With
point counts, you select, say, 10 points at random in your plot, using a map with
a baseline grid of 20m by 20m squares. The points (or 20m x20m squares) chosen
must be at least 150m apart so that you don't count the same birds twice, and
you continue selecting points at random until this condition is met. You will
have to spend 6 to 20 minutes at each point - decide how long beforehand - and
count everything you see or hear from each point. Point
counts are useful because not only do you get an index of the abundance of each
species in the wood, but you can also relate your results to the habitat at each
point - and find which habitats are preferred by which species. The habitats within
the woodland can vary dramatically. But
point counts are not easy to do in Oak Glen because of the roughness of the terrain.
Nor is the plot size (65 acres) large enough to give you a sufficient number of
'hits' to make your results statistically significant, except for the most numerous
species. Unfortunately,
the same applies to the transect counts I did in Oak Glen - they didn't provide
a sufficient number of records for most species. In
all I made 16 visits to the site, comprising two transect counts, two point counts,
one visit at dusk to look for crepuscular species, and 11 casual visits. I believe
I obtained sufficient data to provide a comprehensive bird list for the site,
as well as indices of abundance which, if not completely significant in all cases,
will at least provide a good indication of trends. I
recorded 44 species altogether. Eight of these were casual visitors or 'fly-overs'
such as Swift and Raven, which were not dependent on the site or nesting there. There
were 22 species nesting in the Oak Glen, while the remaining 11 species were nesting
in other habitats alongside, such as the more mature woodlands and the riverbank.
The edge effect: two habitats: the sum is greater than the individual parts. Large
and attractive species included Pheasant and Woodcock, both nesting in the Oak
Glen, and Long-eared Owl and Jay, both nesting adjacent to the Glen. The
club of 22 species nesting in Oak Glen were comprised of thrushes, tits, finches,
warblers, and some other common species. The
best indicator species were in my opinion the warblers. Perhaps unusually for
such a small site, there were five different kinds of warblers nesting in the
Oak Glen. I would like to compare the warblers to Darwin's finches in the Galapagos
Islands, as they are all related but occupy different niches. But unlike Darwin's
finches, these birds are not restricted to Ireland, they have very wide ranges,
and they are all summer migrants, moving between Africa and Ireland every year. At
the moment, the willow warbler is easily the most abundant warbler in Oak Glen,
nesting especially in the regenerating birch. (Number: about 30.) The
whitethroat is also quite common, (Number: about 12) while as many as six grasshopper
warblers were heard in song on one count - quite a high number for this very skulking
species which likes long wet grass and scrub. The
patch of mature trees provided the habitat for two pairs of Blackcaps, while the
only Chiffchaff recorded occurred at the edge of the patch, on the perimeter of
the Oak Glen. As
the woodland matures, however, the Grasshopper Warblers will disappear entirely,
the Whitethroat will disappear too, but more slowly, while the Willow Warbler
will probably occur indefinitely, so long as there are birch. Blackcap and Chiffchaff
should increase steadily however. And many years from now, when we have a tall
closed canopy of oak trees, there is a distinct possibility that another warbler,
the Wood Warbler, will make an appearance. We may even see Lesser Whitethroat,
though that is a remote possibility. All
of these birds are warblers and summer migrants, and documenting their future
rise and fall in Oak Glen - and relating it to habitat changes - would make a
fascinating long-term study. At
present it is difficult to compare results with other plots - so few plots have
been surveyed in Ireland, and they vary so greatly. But as more and more plots
are surveyed, we will accumulate a body of data and it will gradually become easier
to see how much progress we are making with our new woodland plantations and our
woodland conservation efforts. Q
& A Session
Noel
Foley: You were mentioning that foresters took a long time to discover
the environment, but I would also say it took environmentalists a while to discover
plantation forestry in so far as it's only now, and some of this is being funded
by COFORD, that environmentalists are studying the environment of plantation forestry,
so it's not just one way it's a two way process. Another
comment I want to make, and I think you brought this out well yourself, is that
it takes a long time to make a woodland. The birds that you are discovering there
now apart from the mature copse, would have appeared if the place was fenced off
anyway. They are feeding off the seeds of the vegetation that's growing rather
than on the trees, it's going to take generations for a woodland to develop and
I think that has been another problem in so far as people have studied mature
woodland, canopy woodland and when they did not find the same species on the plantation
woodlands there was a general air of disappointment, but the plantation woodlands,
in terms of the journey through time, are only at the start of the journey. The
Oak Glen is going to go on for centuries, it's only starting now. Response:
The Oak Glen is mostly open heath or scrub still, it's not really woodland as
yet. All the species that I recorded are not typical woodland species, they are
more birds of open heath and scrub. They are relying on the vegetation between
the trees, like brambles, and actually I'm not sure if Coillte appreciate that
fully, because in order to assist the Oaks to come along, they trample and spray
in the middle of the breeding season, Tony
Cohu: May I ask are you going to continue the monitoring, and if so how
often will you survey? Response:
From my point of view I thought that the transect method was the easiest to carry
out because you only have to do two visits at dawn per annum. So I thought that
either I would continue it every year or because it's such a straightforward system
anybody could do it, so that we will have a record over fifty years if this same
system is followed every year. I was looking for a system that could be repeated
annually for this reason. All it takes is two visits of about two to three hours,
one in April and one in May. Linda
Murphy: From the point of view of environmental assessment, you mentioned
April and May were the best times to review the area. Would you say therefore
that a survey taken in late autumn or winter was incomplete from a point of view
of the birds present on the site? Response:
I did think that perhaps I should add a winter survey as well in order to be complete
because you do get winter visitors that would not be there in the summer. But
very few, basically some thrushes, redwings and fieldfares, so it would be a good
idea to include a third visit, maybe in November, December or January to find
out if there is any other differences at that time. Noel
Foley: I would have thought that two survey times would have been better
than one survey time. But a thing that worries me a small bit is the fact that
you are using the plantings along the roadways, is there not a danger over time,
in so far as I presume over time in a place like the Oak Glen with nearby heavy
centre of population you are going to get some level of human activity which could
make the habitat along the roadways different from the habitat in the main body
of the woods. Would this skew the results if you want to make a comparison over
time. Response:
The disturbance factor I would rule out because it's a very lightly used place,
not many people go there, surprisingly, and the birds are not affected by people
just walking along, it's only if the people are actually pursuing them that they
are likely to be affected, so the human element is not going to affect your results. You
are right though in that the paths are quite narrow so it's quite easy to see
and hear what is on both sides of the aisles as you are going along, but I was
simplifying things in my description. I actually climbed over the fence and walked
down around the perimeter fence as well in order to make the progress slightly
different, and thus get to see more species.
"Books!
'tis a dull and endless strife: Come, hear the woodland linnet, How sweet
his music! on my life, There's more of wisdom in it. And
hark! how blithe the throstle sings! He, too, is no mean preacher: Come
forth into the light of things, Let Nature be your Teacher." William
Wordsworth, 'The Tables Turned'. |
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