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Breeding bird populations offarmland in mid-west Ireland in 1987L. S. Lysaght aa Department of Geography , Trinity College , Dublin 2,IrelandPublished online: 24 Jun 2009.

To cite this article: L. S. Lysaght (1989) Breeding bird populations of farmland in mid-westIreland in 1987, Bird Study, 36:2, 91-98, DOI: 10.1080/00063658909477010

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Bird Study (1989) 36, 91-98

Breeding bird populations of farmland in mid-westIreland in 1987

L. S. LYSAGHT, Department of Geography, Trinity College, Dublin 2,Ireland.

The breeding bird populations of 5 farmland plots in mid-west Ireland were cen-sused during 1987. The results show that Wren, Robin, Blackbird, Dunnock andChaffinch are the most common species, with the Wren being numerically domin-ant in all plots. The Wren and Robin form a much greater proportion of the farm-land bird populations than in Britain. Reasons for this difference are discussed.

IL ighty three per cent of Ireland is farmland'and as such is the most extensive breeding

habitat available to birds. Despite this, very lit-tle is known about the breeding bird commun-ity of farmland in Ireland. This is in markedcontrast to Britain where the Common BirdsCensus, a co-ordinated national survey offarmland and woodland birds, has been inexistence since 1962. 2 A considerable amountof published information also exists on dif-ferent aspects of farmland birds in Britain. 3 Asthe impact of modern agricultural practices onbird populations is most noticeable in the areasof intensive production, it is understandablethat the majority of published material ema-nates from the lowland farms of England. Inthese regions, agriculture is intensive andevery available piece of land is brought intoproduction.

The agricultural landscape of mid-west Ire-land differs considerably from that of lowlandEngland as agriculture is less intensive. Thelandscape is dominated by a relatively densenetwork of unmanaged hedgerows connectingsmall patches of scrub and waste ground.There is very little arable land, the vast major-ity of the region being grassland, often of poorquality. This combines with the milder andwetter climate of mid-west Ireland to create anenvironment unlike that of lowland Englandand this difference is reflected in the bird com-munity.

The objectives of this paper are twofold: firstto present the results of 5 censuses of the

breeding bird populations of farmland in mid-west Ireland to provide data against whichstudies undertaken in other regions of Irelandcan be compared, and second, to describe thefarmland populations of a number of plotswhere agriculture is not intensive and wherethere is a considerable amount of unmanagedand neglected habitat. In Ireland, there is onlyone previous study of farmland birds,' the re-sults of which remain largely unpublished.'

METHODS

The breeding bird population was censusedusing the mapping method' as standardizedby the International Bird Census Committee.'Five plots were chosen for their conveniencebut, nevertheless, provided a good cross-sec-tion of the different farming types of the region(Fig. 1 & Table 1). The size of the plots was justunder the minimum area recommended by thecommittee. There were 2 reasons for this. First,this census work was part of a detailed investi-gation into habitat preferences of hedgerownesting birds for which the total length ofhedgerow rather than the area of the plots wasthe controlling factor. Second, the high densityof hedgerows and the large area of scrub insome of the plots meant that census work wasvery time consuming, thus reducing the totalarea which could be comfortably censused on asingle visit. Eight full visits, and a number ofpartial ones to locate the boundaries of difficultterritories, were made to each plot from 1 April

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•CAHERCONLISH

LIMERICK CITY

Principal road

Village

River f

5 km

92 L. S. Lysaght

Figure 1. Location of the farmland plots: (1) Cratloekeel, (2) Ballycannan North, (3) Sandylane,(4) Fanningstown, (5) Briskamore.

Table 1. Main habitat features of the 5 plots

Cratloekeel Ballycannan Sandylane Fanningstown Briskamore

Grid reference R 5160 R 56 62 R 68 51 R 58 47 R 50 51

Farming activity Dry cattle Dry cattle,Dairying

Dry cattle,Dairying

Dairying,Sheep

Dry cattle,Tillage,Sheep

Total area (ha) 37 36 35 38 35

No. of fields 16 16 13 15 16

Mean field size (ha) 2.2 2.2 2.6 2.4 2.2

Largest field (ha) 8.1 10.1 6.8 8.9 7.3

Total hedgerowlength (m) 4513 4848 5025 4767 5505

Hedgerows withtrees(m) 1597 2525 2188 116 1004

Low trimmedhedgerows(m) 337 0 0 I275 3146

Hedgerow basalarea (m2 ) 20555 55061 28261 22504 32441

Area of scrub (m2) 5090 13398 0 0 1670

Tilled land (ha) 0 0 0 0 16.4

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Farmland birds in Ireland 93

to 20 July 1987, the combined total being in ex-cess of 150 hours.

The number of breeding pairs of Corvidae,Swallow* and Starlings was estimated bycounting the number of nests found. As Star-lings sometimes nest colonially, additional ob-servations were made of the birds entering andleaving the nest sites, particularly when theyoung birds were being fed, to determine thenumbers of breeding pairs.

An attempt was also made to estimate thenumbers of breeding Woodpigeons Columbapalumbus by locating nests, but in some areaswhere the scrub was particularly dense accesswas virtually impossible, so a reliable popula-tion estimate could not be produced. Thus,while Woodpigeons bred commonly in allplots, they are omitted from any further con-sideration. As the areas of the plots vary, thedensity of birds per 10 ha was calculated foreach species to facilitate a comparison of plots.

RESULTS

Breeding density and number of species

The census results from the 5 farmland plotsare shown in Table 2. A total of 485 territoriesbelonging to 32 species was mapped, givingan average breeding density of 26.9 pairs. Thehighest density of birds was at BallycannanNorth with 43 pairs, where 154 territories be-longing to 27 species were mapped. Sandylanehad the next highest density of breeding birdswith 27.5 pairs. Here 24 species held a total of95 territories. Cratloekeel had a similar densitywith 26 pairs, but the 95 territories mapped be-longed to only 17 species. Territories of 17species were also mapped at Fanningstown,but the density of birds was considerably lowerat 21.8 pairs. The lowest density of birds was16.5 pairs at Briskamore where 16 species ac-counted for 58 territories.

Individual species

On a purely arbitrary basis, Fuller 8 suggeststhat a species can be regarded as typical of acommunity if it occurs in half or more of theplots censused from that community. Usingthis criterion, 21 species can be considered as

*Scientific names are given in Table 2.

typical of the bird community of mid-west Ire-land. Five species were dominant, Wren,Robin, Blackbird, Dunnock and Chaffinchwhich together comprised between 61% and72% of the total population (Fig. 2). The Wrenwas by far the most abundant species account-ing for 107 of the 485 territories mapped, or onaverage 22% of the total population. This valueranged from 19% of the community at Sandy-lane to 25% at Fanningstown, however, theproportion of Wrens in each of the 5 plots wasnot significantly different (x = 1.15, P > 0.1).The density of breeding Wrens also varied con-siderably between plots. The lowest densitywas recorded at Briskamore with 3.4 pairs.Cratloekeel, Sandylane and Fanningstownhad similar densities of 4.9, 5.2 and 5.5 pairs re-spectively. An exceptionally high density of9.8 pairs was recorded at Ballycannan North,compared with an average density of 3.2 pairsfor South-west England, the region of Britainwhere breeding densities are highest. 3

The Robin, Blackbird, Dunnock andChaffinch were the next commonest speciesaccounting for 12%, 12%, 11% and 9% respec-tively of the territories mapped from all of theplots. The proportions of these 4 species didnot differ significantly between plots(xi = 7.093, P> 0.1), however, their relativepositions of dominance varied. At BallycannanNorth the species followed the above order.The Blackbird, Dunnock and Chaffinch occur-red in equal abundance at Cratloekeel andSandylane. The Dunnock was the second com-monest species at Fanningstown, followed byBlackbird, Robin and Chaffinch, while at Bris-kamore the Blackbird was the second com-monest species, followed by Robin, Dunnockand Chaffinch.

Only 4 other species, Willow Warbler, BlueTit, Goldcrest, and Song Thrush, bred in all 5plots, with average breeding densities of 1.2,1.1, 1, and 0.8 pairs respectively. A further 4species, Great Tit, Spotted Flycatcher,Meadow Pipit and Starling, were present in 4of the plots. Being colonial breeders the Star-ling and Greenfinch can be one of the domin-ant species in plots where breeding conditionsare favourable as at Fanningstown and Briska-more, but their distribution is more local thanthat of the 5 dominant species.

Eleven more species were recorded in only 1or 2 plots. These can be grouped into species

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94 L.S. Lysaght

Table 2. The census results from the 5 plots, showing the number of territories mapped for each species

Species Cratloekeel Ballyeannan Sandylane fanningstown Briskamore

WrenTroglodytestroglodytes 21 35 18 21 12

RobinErithacusrubecula 14 19 11 8 6

Blackbird Turdusmerula 11 17 10 10 8

DunnockPrunella modularis 11 12 10 12 6

ChaffinchFringillacoelebs 11 11 10 6 5

Willow WarblerPhylloscopustrochilus 2 10 3 5 2

Blue Tit Paruscaeruleus 3 6 5 3 3

GoldcrestRegulusregulus 5 6 2 3 1

Song ThrushTurdusphilomelos 3 5 3 1 2

StarlingSturnusvulgaris 3 0 3 6 1

JackdawCorvus monedula 0 2 4 0 2

Great Tit Parusmajor 3 2 2 1 0

GreenfinchCarduelis chloris 0 1 0 1 5

Coal Tit Parus ater 3 2 1 0 0Chiffchaff

Phylloscopuscollybita 1 5 0 0 0

Mistle ThrushTurdusviscivorus 0 2 1 0 2

Long-tailed TitAegithaloscaudatus 1 3 1 0 0

BullfinchPyrrhula pyrrhula 1 3 0 1 0

Swallow Hirundorustica 0 2 1 0 1

TreecreeperCerthia familiaris 0 2 2 0 0

Spotted FlycatcherMuscicapa striata 1 1 1 0 1

Meadow PipitAnthuspratensis 0 1 1 1 1

Reed BuntingEmberizaschoeniclus 0 1 1 2 0

MoorhenGallinula chloropus 0 0 2 1 0

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Table 2, continued.

Farmland birds in Ireland 95

Species Cratloekeel Ballycannan Sandylane Fanningstown Briskamore

Magpie Pica pica 0 2 0 0Pied Wagtail

Motacilla alba 1 1 0 0 0Snipe Gallinago

gallinago 0 1 0 0 0Skylark Alauda

arvensis 0 0 0 1 0Hooded Crow

Corvus corone 0 0 0 0Grey Wagtail

Motacilla cinerea 0 1 0 0 0Goldfinch

Carduelis carduelis 0 1 0 0 0Linnet

Acanthiscannabina 0 0 1 0 0

Total no. ofterritories 95 154 95 83 58Number of species 17 27 24 17 16

that breed at low densities throughout the reg-ion and those that have specific breedingrequirements that are seldom satisfied onfarmland. The former includes the Tree-creeper, Magpie, Pied Wagtail, Goldfinch, Lin-net and Hooded Crow with the Chiffchaff,Grey Wagtail, Moorhen and Snipe falling intothe latter group. The Skylark would alsoappear to belong to the latter group as it is a re-latively common breeding bird in the uplandareas of mid-west Ireland.

Summer migrants

Summer migrants were poorly represented ac-counting for only 36 of the 485 territories, or8% of the total. The greatest representation ofsummer migrants was at Ballycannan Northwhere they comprised 12% of the population.In the 4 remaining plots their representationwas reasonably constant ranging from 7% atBriskamore, through 6% at Fanningstown and5% at Sandylane, to 4% at Cratloekeel. Theproportion of summer migrants in each plotwas not significantly different (x = 6.42P> 0.1).

Only 4 species of summer migrants, WillowWarbler, Chiffchaff, Spotted Flycatcher andSwallow were recorded from the plots. Willow

Warbler was the most abundant accounting forjust over 60% of all the summer migrant ter-ritories mapped. The breeding density for thisspecies varied considerably between plots.The lowest density was at Cratloekeel and Bris-kamore where there were 0.6 pairs, rising to0.9 pairs at Sandylane and 1.3 pairs at Fan-ningstown. At Ballycannan North where con-ditions would appear ideal for this species thebreeding density was much higher at 2.8 pairs.

Six Chiffchaff territories were mapped, 5 atBallycannan North with the remaining one atCratloekeel. The breeding density of 1.4 pairsat Ballycannan North would appear to be ex-ceptionally high for farmland, as Chiffchaff aretypical of old deciduous or mixed woodlandwhere there are many tall trees to use as song-posts and an abundance of rough under-growth for nesting. 9 In this plot the territorieswere concentrated on the tall scrub and en-compassed only a few of the taller hedgerowsabutting from it.

DISCUSSION

The interpretation of these results is difficult asthey are based on only one year's data. Consid-erable care should be taken, therefore, whenusing these figures to compare with other

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Fanningstown Bri skomore

9.6% 12.0

Sondylane

18.9%

37.9 %

116%^

10.5 %

10.5

Cratloekeel

11.5%

11.5%

Ballycannan North

96 L.S. Lysaght

Figure 2. The structure of the bird populations, showing the number of territories of the 5 com-monest species as a percentage of the total number of territories in each plot n Wren, ®Robin,

Blackbird, ® Dunnock, CI Chaffinch, ❑ Others.

studies, as at best they can only be expected toprovide guidelines of general differences in thefarmland bird community. For this reason, di-rect comparisons with the results of other indi-vidual studies were avoided. Nevertheless,some general conclusions can be drawn.

The most striking feature of the bird popula-tions of mid-west Ireland is the dominant pos-ition of the Wren and Robin. This is in markedcontrast to Britain where the majority of farm-land plots have Blackbird, Skylark orChaffinch as their most abundant species. 3

These authors noted, however, that if theCommon Birds Census data are analysed on aregional basis, Wren and Robin show markedeast—west increases in breeding density, with

the former breeding at greatest densities insouth-west England and the latter in Wales.This trend is so pronounced that in south-westEngland the Wren is numerically dominant in16% of all Common Birds Census plots whilein Wales the Robin is dominant in 20%. In allother regions of Britain these species are neverdominant in more than 6% of plots. In thewestern regions of Britain, therefore, these 2species assume a greater importance thanelsewhere, and the results of the present studywould indicate that this trend extends furtherwestward into Ireland.

The milder climate of the west and the grea-ter availability of suitable breeding habitatprovided by the high density of hedgerows

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Farmland birds in Ireland 97

associated with the western pastoral regionshave been cited as possible reasons for theeast-west increase noted in Britain.' Assumingthat one year's data are representative of thefarmland bird community in mid-west Ireland,then these factors might equally be expected tocontribute to the prominence of the Wren andRobin in the Irish plots.

The availability of suitable nesting habitat isan important factor in determining breedingdensities of most species. In Britain, the breed-ing densities of the Wren and Robin appears tobe influenced by some habitat factors. O'Con-nor10 in his analysis of the CBC data found thatthe breeding densities of these two specieswere positively correlated with hedgerowabundance; Benson & Williamson" - and Ar-nold 12 both emphasized the importance oftrees; while Osborne13' 14 found that Wrensshowed a preference for shrub-richhedgerows. In Ireland, Moles' found thatWrens kept to low scrub in winter, only mov-ing up into taller habitat in summer, while theRobin seemed to require tall trees throughoutthe year. The abundance of tall overgrownhedgerows in the plots of mid-west Ireland islikely to provide suitable nesting habitats forboth these species. However, other speciesalso appear to be influenced by some of thesefactors, so knowledge of the habitat prefer-ences of the Wren and Robin is as yet in-sufficient to identify habitat characteristics thatmight explain their prominence in mid-westIreland. The availability of suitable nestinghabitat is unlikely to explain fully this promi-nence as the majority of hedgerows are thickand overgrown, the structure that is consi-dered most favourable for many species. 15

Climate has a considerable influence onWren and Robin populations. Because of itsdiminutive size the Wren is extremely suscep-tible to cold weather and as a result popula-tions fluctuate more from year to year than forany other species monitored by the CommonBirds Census.' Breeding densities of the Robinare also known to fluctuate widely on farmlandin accordance with climate. After severe win-ters, such as the particularly harsh one experi-enced by Britain in 1962-1963, the breedingdensity of Robins can fall quite dramatically onfarmland,' and after a sucession of mild win-ters populations can increase by up to 60%."As the mean January temperature of mid-west

Ireland is over 5°C, 16 it is relatively mild duringthe winter months, and as there has been novery severe winter in mid-west Ireland since1982-1983 the present populations of the Wrenand Robin are unlikely to be adversely affectedby climate. However, as populations of resi-dent British species are regulated by climate inwinter and by density-dependent behaviour insummer, 17 the influence of the milder climatein Ireland is, in itself, unlikely to be the onlyreason for the observed difference.

A further factor that may contribute to theprominence of the Wren and Robin in the Irishplots is the island biogeographic effect. 18 Bri-tain is generally regarded as the species poolfor Ireland, with only approximately 60% ofBritish landbirds breeding in Ireland. 19-21 Is-land communities are characterized by a de-pauperate fauna, 22 with the more adaptablespecies being more prominent, due to densitycompensation23 or density stasis. 24 The Wren isa rare bird in its primaeval habitat, 25 but it ap-pears to have adapted very successfully to thefragmented habitat of farmland. 26 Withinfarmland there is also evidence of its adapt-ability. Williamson27' 28 and Benson & William-son" showed that in years when populationlevels were low the majority of Wren territorieswere located in well wooded habitats, withwhat were regarded as sub-optimal habitatsbeing used more frequently when populationlevels were high. There is some evidence tosuggest that the same may be true for theRobin."

The favourable conditions created by themild climate and the abundance of tall, un-managed hedgerows obviously contributes tothe prominence of the Wren and Robin in mid-west Ireland, but these conditions are probablyalso favourable to many other species. It islikely, therefore, that the principal reason forthe prominence of the Wren and Robin in mid-west Ireland is their ability to exploit more suc-cessfully the available resources of farmland,due primarily to their adaptability.

The results presented in this paper suggestthat the farmland bird community of mid-westIreland is considerably different from that ofBritain. Further research needs to be under-taken to identify the precise nature of these dif-ferences, and to provide explanations forthem. It would also be interesting to determinethe extent of year-to-year variation in the bird

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98 L. S. Lysaght

community and examine any regional varia-tion that may exist within Ireland.

ACKNOWLEDGMENTS

I thank M. McMahon, P. McNamara, J.Finucane, S. Condon and F. Smith for allow-ing me to work on their farms. Thanks are alsodue to my supervisor Dr R. Alexander, Dr R.Fuller, Dr R. Moles, D. Redmond, and Dr T.Stowe for comments on earlier drafts of thispaper. Financial support for post-graduate re-search from the Department of Education andLimerick Corporation is acknowledged.

REFERENCES

1. Webb, R. (1985) Farming and Wildlife. Forest andWildlife Service, Dublin.

2. Marchant, J.H. (1983) Common Birds Census In-structions. British Trust for Ornithology, Tring.

3. O'Connor, R.J. & Shrubb, M. (1986) Farming andBirds. University Press, Cambridge.

4. Moles, R. (1975) Wildlife diversity in relation tofarming practice in County Down, N. Ireland. Ph.Dthesis: Queen's University of Belfast.

5. Moles, R. (1982) A study of some bird com-munities of the Burren, Co. Clare. IrishNaturalists Journal, 20, 419-423.

6. Enemar, A. (1959) On the determination of thesize and composition of a passerine bird popula-tion during the breeding season. Var Faigelvarld,18, suppl. 2.

7. International Bird Census Committee. (1969)Recommendations for an international standardfor a mapping method in bird census work. BirdStudy, 16, 249-255.

8. Fuller, R.J. (1982) Bird Habitats in Britain. Poyser,Calton.

9. Sharrock, J.T.R. (1976) The Atlas of Breeding Birdsin Britain and Ireland. Poyser, Calton.

10. O'Connor, R.J. (1984) The importance of hedgesto songbirds. In Agriculture and the Environmentpp. 117-123. University Press, Cambridge.

11. Benson G.B.G. & Williamson, K. (1972) Breed-

ing birds of a mixed tarm in Suffolk. Bird Study,18, 34-50.

12. Arnold, G.R. (1983) The influence of ditch andhedgerow structure, length of hedgerows andarea of woodland and garden on bird numberson farmland. Journal of Applied Ecology 20, 731-750.

13. Osborne, P. (1982) The effects of Dutch Elm diseaseon farmland bird populations. D. Phil. thesis, Ox-ford University.

14. Osborne, P. (1984) Bird numbers and habitatcharacteristics in farmland hedgerows. Journal ofApplied Ecology, 21, 63-82.

15. Pollard, E., Hooper, M.D. &Moore, N.W. (1974)Hedges. Collins, London.

16. Meterological Service, Dublin (1979) In Atlas ofIreland, p. 30. Royal Irish Academy, Dublin.

17. O'Connor, R.J. (1981) Comparisons betweenmigrant and non-migrant birds in Britain. InAnimal Migration (ed D.J. Aidley), pp. 167-195.University Press, Cambridge.

18. MacArthur, R.H. & Wilson, E.O. (1967) TheTheory of Island Biogeography. University Press,Princeton.

19. Lack, D. (1969) Number of bird species on is-lands. Bird Study, 16, 193-209.

20. Lack, D. (1976) Island Biology. Blackwell Scien-tific Publications: Oxford.

21. Reed, J. (1981) The number of breeding landbirdspecies on British islands. Journal of Animal Ecol-ogy, 50, 613-624.

22. Udvardy, M.D. (1969) Dynamic Zoogeography.Van Nostrand Reinhold Company: New York.

23. MacArthur, R.H., Diamond, J.H. & Kerr, R.K.(1972) Density compensation in island faunas.Ecology, 53, 330-342.

24. Williamson, M. (1981) Island Populations. Univer-sity Press, Oxford.

25. Wesotowski, T. (1983) The breeding ecology andbehaviour of Wrens Troglodytes troglodytes underprimaeval and secondary conditions. Ibis, 125,499-515.

26. Ford, H.A. (1987) Bird communities on habitatislands in England. Bird Study, 34, 205-218.

27. Williamson, K. (1969) Habitat preferences of theWren on English farmland. Bird Study, 16, 53-59.

28. Williamson, K. (1971) A bird census study of aDorset dairy farm. Bird Study, 18, 80-96.

(MS received 18 February 1988; revised MS accepted 8 August 1988)

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