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The Birds of Irish Bog

Introduction

Since the last glaciation peat bogs of various kinds developed to cover a large proportion of NW Europe; that original extent now considerably reduced by the activities of man. The bog plants, whose remains have resulted in these accumulations of organic matter, show a high degree of specialisation and adaptation to grow and prosper in this inhospitable environment that is characterised by extremes of acidity, low nutrient status, wetness and exposure. In contrast there is not a single bird species confined to bogs in the Western Palaearctic. Instead a number of bird species have developed strong affinities with this habitat mostly utilising it as a breeding habitat, with the majority ground nesting. Bogland avian communities are thus typically poor in species but have abundant individuals of one or two dominant passerines such as Meadow pipit Anthus pratensis and Skylark Alauda arvensis, both of which are ground-dwelling omnivores. Numbers of species and their abundance are associated with bog size, habitat patchiness and structure, and the proportion of open water (for example see Bolscher 1995, Fuller 1982).

The birds of Irish bogs have not been subjected to national surveys despite the significant area of raised bog and blanket bog in the countryside. The Countryside Bird Survey, launched in 1998, comes closest to meeting that requirement on a sample basis but analysis of the data is only commencing now. So our knowledge and understanding arises from a series of wider ecological surveys starting with investigations focussed on Red grouse Lagopus lagopus scoticus on blanket bog at Glenamoy, Co Mayo in the 1960s and 1970s (Watson and O'Hare 1979). The studies of MacLochlainn (1984) at Glenveagh National Park in Co Donegal and Haworth (1987) in Connemara, Co Galway followed. A synthesis of the information available at the time on the birds of raised bogs is included in Cross (1990).

Subsequently two PhD studies on the impacts of drainage and woodland on the breeding birds of raised bogs were carried out by Thomas Pohler and Birgit Huvendick at Clara, Raheenmore and All Saint's bogs in the Irish midlands. These, the work of Feehan and O'Donovan (1996) and various observations by colleagues and myself over the years constitute the basis of this account.
Bogs at first glance may be seen as bleak, boring and uniform environments. But this is not the case. They show considerable natural variation, both within and between bogs, in surface topography, extent and seasonality of open water and the composition and structure of the vegetation. Man, principally through cutting and drainage activities, has introduced further variation. In so far as the available information allows this account will seek to recognise this variation and link the breeding and wintering birds to it. In particular it will seek to identify the bird communities of open intact bog, those of the natural features that occur on or are associated with bogs, e.g. flushes, soaks, lakes, rivers, trees and areas of woodland, and those of anthropogenically related change. The bog's role in the life cycle of these species will also be covered.

The Birds of Open Bog

Traditionally the Red Grouse has been considered the most characteristic bird of our bogs. Undoubtedly this arises from its original popularity as a game bird with evidence present on many of our remaining bogs today, systems of shallow parallel drains and lines of shooting butts, of the efforts of landowners to manage these areas for grouse and grouse shooting. It is unique amongst the suite of birds found on bogs in that it can, without recourse, complete its entire life cycle there. There the presence and abundance of heather Calluna vulgaris as food, cover and nesting habitat determines its presence and abundance. Heather may appear to be everywhere but it is particular in its requirements. It only becomes luxuriant and dominant where drier and better-drained conditions exist. Grouse are still present on some raised bogs and widely distributed on blanket bogs where densities are naturally low, probably less than one bird per 40 ha. It never attains the densities recorded on heaths where the shallower peats and sloping ground provide drier conditions for the growth of heather. It is likely that the over-grazing of the blanket bogs has reduced this density estimate further. Continuing reduction in size, isolation and fragmentation of bogs further threaten to reduce the distribution of the species and its abundance.

As you traverse the open bog in spring these days there is therefore a decreasing likelihood of hearing a Grouse call but the air will be filled with the songs of the recently arrived Meadow pipits and Skylarks as they compete for breeding territories. Meadow pipits are nearly always more numerous than Skylarks and often by up to a factor of two to one or even three to one in some blanket bog areas, greatly outnumbering any other species. They nest on the ground, laying three to six eggs per clutch and raising two and, depending on altitude, possibly up to four broods in the case of the Skylark. They congregate in separate flocks usually from late July onwards and have largely departed the bogs before the onset of winter.

These two species are the principal prey of the Merlin Falco columbarius and the bogs, together with the uplands generally, are its main hunting and breeding grounds. Presence of Merlin is most easily established by looking for their plucking posts within the bog, on hummocks or boulders or at the edge on prominent turf banks or fence posts. Viewed traditionally as a ground nester, recent survey work (D Norriss pers comm.) shows the Irish population is now primarily tree nesting, with most nests located on the wooded perimeters of the raised bogs and the conifer plantations established on blanket bogs. Here it occupies the old nests of the Grey or Hooded crow Corvus corone cornix. The last record of ground nesting on raised bogs was c. 20 years ago in Co Westmeath where a pair bred successfully in two consecutive years on a small heather covered islet in a complex of pools (J Moore, pers comm.). Some heather clad lake islands or those with stunted woodlands in the western blanket bogs are still used as nesting sites. Although adult Merlin remain within their breeding territories on raised bogs year round, the young disperse. Consequently the species cannot be regarded exclusively as a year round resident of the bogs.

Snipe Gallinago gallinago, Curlew Numenius arquata and Golden plover Pluvialis apricaria all nest on the bogs, the latter species confined to the western blanket bogs between Cos Galway and Donegal. Nest sites are always close to wet areas such as Sphagnum lawns, flushes and pool systems that are essential feeding areas for their insectivorous chicks. At this time the adults largely feed on adjacent pastures and wetlands, their favoured habitat in winter. Snipe will use undisturbed bogs as daytime roosts in winter when numbers are swelled by the influx of Icelandic migrants.

Golden plover is one of the few breeding species that show specific adaptations to breeding on bogs. Amongst waders they lay the largest egg and have the longest incubation period for their size. This is seen as a means of importing nutrients and reducing the chick's dependence on the bog before fledging.
While it is possible to see almost any bird flying over the bogs, certain species use it more purposefully. Hovering Kestrels Falco tinnunculus and quartering Hooded crows and Ravens Corvus corax are seeking food. Small mammals and birds together with large invertebrates are the quest of the Kestrel and carrion, principally sheep, probably sustains large populations of the latter two species on blanket bogs where isolated trees and nearby cliffs provide suitable nesting sites.

The Greenland White-fronted goose Anser albifrons flavirostris or 'bog' goose is a winter visitor with a traditional and specialised association with bogs (see box). Another arctic species which may be flushed during winter as it feeds amongst the vegetation is the rare Snow bunting Plectrophenax nivalis. (This next section can be placed in a box if required)

[The distribution of the Greenland White-fronted Goose in Ireland, and in Scotland and Wales, coincides with the climatic template that engenders the formation of oceanic blanket bog. These bogs, together with the midland raised bogs are bounded by the four-degree January isotherm and hence rarely freeze. They constituted the species' traditional habitat before the influence of man began to change things. The species feeds by probing for the nutritionally rich underground storage organs of Cotton grass Eriophorum angustifolium and White-beaked sedge Rhyncospora alba. Extraction of the plants is easiest where the bog substrate is softest and these areas are characterised by pools and hummocks and quake underfoot. Wet areas such as these make up a relatively small proportion of the total bog area, vary considerably in size and are not distributed evenly. Strong evidence of high site fidelity, a well developed social structure involving extended family relationships and small flock size all suggest that the species is highly adapted to exploit this unevenly dispersed and perhaps, rotationally used, food resource. Bog feeding still pertains in Iceland and Greenland, the staging area on spring and autumn migration and breeding area respectively.

For many goose species worldwide traditional habitats on the wintering grounds have been progressively lost to programmes of reclamation, drainage and afforestation. Like these other species the Greenland White-front has been able to adapt and take advantage of agricultural grasslands and other crops. So with the gradual disappearance of the bogs, particularly the raised bogs, that link with the bogs is in the process of being broken. In the early years of the Greenland White-front Survey (1982-85) 11 flocks out of 34 continued to use bogs in the midlands and in Cos Kerry, Galway, Mayo, Sligo and Donegal. 0nly eight flocks, mostly on blanket bog, do so presently, and on a much more reduced basis, despite the population in Ireland increasing from c. 9-10,000 then to c. 13-14000 now (Fox et al 1994).]

The Birds of Natural Bog Features

Areas of local nutrient enrichment occur in nearly all bogs as flushes, or where these are more extensive, as soaks which can be additionally characterised by small lakes with floating mats of vegetation. Streams and swallow holes may also occur. More plant species are present and the vegetation is generally more luxuriant. For birds the most significant change is the increase in structural complexity of the vegetation, particularly the vertical component, which increases cover and foraging and nesting opportunities. The plants that most notably effect this change are Molinia caerulea, Myrica gale, Juncus effusus and Rubus fructicosus. Scattered trees, mostly Betula pubescens and Pinus sylvestris, may also be present. Small woodlands develop in certain raised bogs, where the canopy is dominated by Betula pubescens, and the under story by Salix species.

Breeding Stonechat Saxicola torquata and Reed Bunting Emberiza schoeniclus are the first species to exploit this situation where nesting cover, perches and better feeding opportunities are now available. They are followed closely by Wren Troglodytes troglodytes. While this latter species is more typically associated with woodland that has a well-developed field and shrub layers, it is the field layer that is the primary requirement and this is what is provided in these locations. Once trees begin to dominate, the usual compliment of breeding woodland birds arrive represented by Robin Erithacus rubecula, Chaffinch Fringilla coelebs, and Willow Warbler Phylloscopus trochilus.

Mallard Anas platyrhynchos, Teal Anas crecca and Moorhen Gallinula chloropus are associated with bog lakes which with their islands and marshy fringes provide suitable nesting and feeding habitat. The seclusion and safety of islands attract a number of colonial breeders. The Grey Heron Ardea cinerea, where islands are covered in scrub woodland, and Cormorant Phalocrocorax phalocrocorax, Black-headed Gull Larus ridibundus and Common Gull Larus canus at certain locations in the western blanket bogs.

Where rivers flow through the blanket bogs Dipper Cinclus cinclus, Grey Wagtail Motacilla cinerea and Common Sandpiper Actitis hypoleucos are most noticeable during the breeding season.
The Wheatear Oenanthe oenanthe requires drier parts of the bog, e.g. where rock or mineral soil protrudes through the blanket bogs or along bog fringes. Holes, necessary as nest sites are only located in these areas.

In these drier areas, particularly if they are sheltered as well, Calluna vulgaris may reach its full growing potential with all the features of miniature woodland. These include many of the woodland birds already mentioned, namely Wren, Robin and the Dunnock Prunella modularis. Other notable observations have been a colony of nesting Twite Carduelis flavirostris in metre high heather near Belderg, Co Mayo and wintering Woodcock Scolopax rusticola using it as daytime roosting cover.

Influence of Man

For centuries, and particularly so over the past 50-60 years, man has modified these bogs through direct drainage and indirectly from the impacts of arterial drainage on the local water table of raised bogs. This, together with peat cutting on the margins, the provision of servicing roads and afforestation, has all lead to a drying out of the bogs which favours the growth of Calluna vulgaris and Molinia caerulea and the appearance of bird species more associated with woodland and hedgerows as outlined above.

The cutaway areas are now extensive and form a veritable complex of habitats including open water, abandoned banks, rough grassland, scrub, broadleaf woodlands and coniferous plantations. These now constitute potentially the richest habitat for birds in the country with upwards of 40 breeding species being confirmed from various studies. This 'habitat', and its birds, is deserving of more conservation consideration and study in its own right.

Future Opportunities and Prospects

Open bog in Ireland is poor in breeding bird species and almost devoid of bird-life in winter. Only Meadow pipit and Skylark are fairly ubiquitous. Natural features and many of man's activities influence the structure and composition of the vegetation positively for birds by increasing cover and providing a combination of additional nesting and foraging opportunities. Certain hedgerow, woodland and wetland species invade and boost breeding species diversity locally. However all species recorded on the bogs occur at higher densities in other habitats which is not surprising given the recent evolutionary history of these bogs.

Comparative work on open raised bogs in NW Europe confirm this pattern of low species numbers and diversity but with their continental location adding a few more species, e.g. Lapwing Vanellus vanellus, Wood sandpiper Tringa glareola and Whinchat Saxicola rubetra. In contrast Stroud et al (1987) showed for the blanket bogs of Caithness and Sutherland in Scotland a much greater diversity and density of breeding birds. This assemblage includes both Red and Black-throated Divers Gavia stellata and Gavia arctica, Dunlin Calidris alpina, Greenshank Tringa nebularia and a number of other rarer waders, Wigeon Anas penelope, Pintail Anas acuta and Arctic skua Stercorarius parasiticus, species more associated with the Boreal sub-arctic. Latitudinal position and climate will probably ensure that many of these species will not breed on Irish bogs.

The continuing loss of the 'total extent' of our bogs and the accompanying diversity of forms that characterise these bogs, fragmentation, increasing hydrological stress and over-grazing makes the future look bleak for the habitat itself and consequently the birds of bogs.

References

Bolscher, B. (1995) Niche requirements of raised bog birds. Matching habitat attributes resulting from bog restoration.(to be provided).
Cross, J. R. (1990b) The Raised Bogs of Ireland: their ecology, status and conservation. Government Stationary Office, Dublin, pp 87.
Feehan, J. and O'Donovan, G. (1996) The Bogs of Ireland: An Introduction to the Natural, Cultural and Industrial Heritage of Irish Peatlands. Walsh Printers, Roscrea, Ireland, pp 518.
Fox, A.D. et al (1994) Greenland White-fronted Geese in Ireland and Britain 1982/83 ­ 1993/94: the first twelve years of international conservation monitoring. GWGS Research Report No. 8, pp 54.
Fuller, R. (1982) Bird Habitats in Britain. Poyser Calton, pp 320.
Haworth, P.F. (1987) Survey of West Galway. Unpublished Report to the WWF (Project 26/86), pp 42.
MacLochlainn, C. (1984) Breeding and wintering bird communities of Glenveagh National Park, Co. Donegal. Irish Birds 2, pp 482-500.
Stroud, D.A. et al (1987) Birds, Bogs and Forestry: The Peatlands of Caithness and Sutherland. Nature Conservancy Council, pp 121.
Watson, A and O'Hare, P.J. (1979) Bird and mammal numbers on untreated and experimentally treated Irish bog. OIKOS 33, pp 97-105.

Copyright Dr John Wilson 2002
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