the bird community of farmland

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This article was downloaded by: [Washington State University Libraries ] On: 11 November 2014, At: 12:29 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Bird Study Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tbis20 The bird community of farmland Kenneth Williams a a B.T.O. , Published online: 19 Jun 2009. To cite this article: Kenneth Williams (1967) The bird community of farmland, Bird Study, 14:4, 210-226, DOI: 10.1080/00063656709476165 To link to this article: http://dx.doi.org/10.1080/00063656709476165 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.

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Page 1: The bird community of farmland

This article was downloaded by: [Washington State UniversityLibraries ]On: 11 November 2014, At: 12:29Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number:1072954 Registered office: Mortimer House, 37-41 Mortimer Street,London W1T 3JH, UK

Bird StudyPublication details, including instructionsfor authors and subscription information:http://www.tandfonline.com/loi/tbis20

The bird community offarmlandKenneth Williams aa B.T.O. ,Published online: 19 Jun 2009.

To cite this article: Kenneth Williams (1967) The bird community offarmland, Bird Study, 14:4, 210-226, DOI: 10.1080/00063656709476165

To link to this article: http://dx.doi.org/10.1080/00063656709476165

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy ofall the information (the “Content”) contained in the publicationson our platform. However, Taylor & Francis, our agents, and ourlicensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication arethe opinions and views of the authors, and are not the views of orendorsed by Taylor & Francis. The accuracy of the Content shouldnot be relied upon and should be independently verified with primarysources of information. Taylor and Francis shall not be liable for anylosses, actions, claims, proceedings, demands, costs, expenses,damages, and other liabilities whatsoever or howsoever causedarising directly or indirectly in connection with, in relation to orarising out of the use of the Content.

Page 2: The bird community of farmland

This article may be used for research, teaching, and private studypurposes. Any substantial or systematic reproduction, redistribution,reselling, loan, sub-licensing, systematic supply, or distribution inany form to anyone is expressly forbidden. Terms & Conditions ofaccess and use can be found at http://www.tandfonline.com/page/terms-and-conditions

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The bird community of farmland

by Kenneth WilliamsonPopulations Research Officer, B.T.O.

INTRODUCTION

THE ENGLISH COUNTRYSIDE provides a mosaic of habitatsperhaps unrivalled in its diversity. It is an artificial environment inthe sense that the greater part of Lowland Britain has been fashionedby man for settlement and food production over the last 2,000 years.In place of the damp oak forests which clothed the river valleysand heavier soils during the Atlantic and Sub-boreal Phases (c.3,500 B.C. onwards) there has gradually arisen a chequered patternof fields supporting grass and a wide variety of other crops, varyingregionally in size, and divided by diverse types of boundary amongwhich the quickset hedge is supreme. The major part of thiscomplex and extremely important hedgerow system is little morethan 200-300 years old in the English Midlands and South: itshistory has been given in some detail by Moore, Hooper and Davis(1967).

The upland areas, even where there has been little improvementof the land by re-seeding, have been similarly affected by man,mainly as a result of burning and intensive grazing by sheep. Herethe hedgerows give way to drystone walls, or to earth-banksovergrown with gorse and bramble—especially with the Celtic fieldsystem of the West. It is doubtful if any considerable extent of`natural habitat' now remains in the Lowland Zone, or in theHighland Zone other than on the exposed summits, and ourbird-life has necessarily had to adapt during recent centuries to alandscape managed—and sometimes mismanaged—by man.

Agricultural land covers more than 29 million acres (117,500square kilometres) of England and Wales, or roughly 80 per cent:of this, 87,150 sq. km. (68 per cent) of England and 10,450 sq. km.(51 per cent) of Wales may be considered `improved' farmland asdistinct from rough hill grazing. Only 6+ per cent of England and9 per cent of Wales are afforested, so there is much justification forregarding farmland as the most extensive bird habitat in ourcountryside.

In view of the history of change from forest to field in the landusage of Lowland Britain it is not surprising that the bird faunaof our present-day farmland is predominantly a `forest' fauna,closely dependent on the remaining woodland edges, copses andplantations, and on the linear scrub along streams, ditches, lanesand field-boundaries, though the larger part of the adaptation tofeatures of this kind cannot be many centuries old. Since farmingpractices vary from one region of the country to another, duesometimes to climate, sometimes to human history and the pressureof modern economics, it is to be expected that the farmland birdcommunity will also vary, perhaps widely, from place to place. Add

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BIRD COMMUNITY OF FARMLAND

to this the vagaries of distribution—which is far from uniform evenwithin so small a country as Britain—and the task of defining afarmland bird community representative of the country as a wholeis an impossible one.

Nevertheless, an outline of the structure of a `typical' farmlandcommunity has been attemped in this paper by considering theCommon Birds Census returns from a restricted region of thecentral English lowlands. This is a part of Britain where the arablelandscape presents the widest variety of scene and the habitat ismost diversified at the present day. It is also a region which islikely to undergo considerable change, due partly to the stressesimposed on the environment by the demands of an expandinghuman population, and partly to the progress in agricultural scienceand the current trend towards large, commercially viable holdingsdedicated to cereal production (Anon. 1966).

For the present, this `typically English' arable countryside isdominated by its wide variety of hedgerows and their attendanttrees. An assessment of hedgerow length with woodland edge, madefrom 29 `habitat maps' supplied by C.B.C. observers in differentparts of England and South Wales, gives an average figure of closeon 12 km. of such cover per sq. km . of the countryside. The same29 maps show that over the three winters 1963-66 hedgerowlength was reduced at the rate of 1.1 yards per acre, or 2.5 metresper hectare, per annum.

Further statistical details, as well as a discussion of hedge typesin different regions and their relative value as harbourers of birdlife, appear in the paper by Moore, Hooper and Davis. There isno doubt, as these authors show and the C.B.C. data confirm, thathedgerows as a bird habitat are being insidiously and seriouslyeroded, more rapidly in some regions (viz. East Anglia) than inothers. There can be little doubt also that the development of theagricultural industry towards a wider dependence on cereal crops(particularly barley), greater mechanisation, reliance on chemicalfertilisers and pesticides, and indoor rearing of livestock, is likelyto accelerate this change during the coming decades (Cornwallis,in press). The time therefore seems opportune for some assessmentof the `carrying capacity' of farmland for breeding birds, and adiscussion of how these are distributed with regard to species anddensity on different cropping types and in different regions ofEngland and Wales.

•THE CENTRAL ENGLISH LOWLANDS SAMPLE

Data derived from a sample restricted to the central Englishlowlands have been used as the basis for a comparison with dataprovided by other farm censuses grouped regionally as follows :Eastern England, South and Southwest England, West Midlandsand Wales, and Northern England. This grouping was adopted forconvenience, to give a sufficient number of returns for a usefulcomparison. Owing to the paucity of Scottish returns and theirwide scatter over a vast area, Scotland is not considered here.

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BIRD STUDY

The sample comprised 28 census returns from the counties ofBuckingham (5), Oxford (4), Hertford (4), Berkshire (1), Warwick(6), Worcester (1), Leicester (2), Rutland (1) and Nottingham (4).The majority of the returns were for 1966, but one 1965 and two1967 returns were included for plots not covered in 1966. Theplots from elsewhere, with which comparisons are made, alsoinclude a few from previous years, but the majority are for 1966.Individual farm sizes in the sample range from 109 to 268 acresand total 5,432 acres or 2,200 hectares.

Of the 28 farms, 12 had 60 per cent or more of the cultivatedpart devoted to cereals, or to cereals and root-crops mixed: theyare located in Bucks. (1), Herts. (3), Oxon. (1), Worcs. (1),Warwicks. (3), Leics. (1), and Notts. (2). Eleven others were pre-dominantly pasture and hay, distributed in Bucks. (3), Herts. (1),Oxon. (2), Warwicks. (1), Leics. (1), Rutland (1), and Notts. (2).The remainder (Bucks., Oxon., Berks., and two in Warwicks.) hadvery nearly equal areas of grain and grass. All the plots have lessthan 12 per cent of `cover' in the form of copses, gardens, orchardsand scrub of various kinds, excluding the field hedgerows. Fromthe point of view of cropping and land use they probably afforda fair cross-section of farming practice in the central EnglishLowland Zone.

DENSITY OF BIRDS ON FARMLAND

Three difficulties militate against an accurate measurement of thebird density on agricultural land. Firstly, not all observers censusall species : indeed, the current C.B.C. Instructions recommend theomission of Woodpigeons, 1 colonial Corvidae and House Sparrowsbecause any attempt to obtain an accurate count would greatlyprolong the time spent in the field, and would almost certainlywork to the detriment of adequate registration of the more im-portant song-birds. Some observers ignore Starlings, Swifts andhirundines, mostly because these nest in farm buildings or privatepremises where access is difficult. All these, together with birds-of-prey (whose territory may cover an area much larger than a singlecensus plot), are omitted from further consideration in this paper.

Secondly, all census plots are bounded by hedges, streams, lanesor woodland-edges, the breeding birds of which introduce an `edgeeffect' which tends to inflate the density figures, the more seriouslythe smaller the plot becomes. For this reason census plots of lessthan 100 acres have not been considered in the discussion ofdensities. Thirdly, the density of individual species (and, of course,of particular farms) changes from year to year, and not all speciesfluctuate in phase. On the vast majority of census plots the totalpopulation, and the numbers of most species, are currently at amuch higher level than immediately after the severe winter ofearly 1963 (Bailey 1967). Four breeding seasons have elapsed sincethen, but we cannot say yet whether or not the 1966 situationrepresents `normality'

1The scientific names of all the species mentioned are listed in the Appendix.

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BIRD COMMUNITY OF FARMLAND

Nevertheless, bearing in mind the limitations imposed by themethod and the nature of the data (for some plots and some speciesundoubtedly receive more complete coverage than others—see Snow(1965), particularly Table I and pp. 302-3) it is possible to get auseful idea of the relative densities of the more important farmlandspecies. Figures, in pairs per 100 hectares, are given for 58 speciesin Table I. The observed ranges within the sample area are shown,together with the means, and the incidence of each species interms of the percentage of plots occupied. All subsequent statementsof density refer to pairs per 100 hectares (=1 sq. km . or 247 acres),this being the most commonly used unit in European census studies.

TOTAL DENSITY ON INDIVIDUAL FARMS

Excluding the species mentioned in the last section as incompletelycensused or not counted at all, the total breeding density onindividual farms in the central Midlands sample shows a widevariation between 110 pairs of 22 species (Worcestershire) to 499pairs of 33 species (Hertfordshire). The majority of these plotshave from 24 to 35 species and the proportion of passerines is alwaysover 90 per cent. In Eastern and Northern England the variationis even wider, as can be seen from the examples in Table II, andthe proportion of passerine pairs in the bird community is frequentlylower. Generally speaking the more uniform the environment (e.g.reclaimed fen and marshland farms) the lower the total and thepoorer the species representation become, while some of the morediversified farms have more than four times the total bird popula-tion and over 40 breeding species.

For most of the farms, densities between 100 and 400 pairs per100 hectares are recorded. Among the low-density plots (TableII (A)) 755 Kent, in the Isle of Thanet, is matched for poverty ofbird-life by two other plots in the same area. The proportion ofSkylarks is high, but not nearly so high as on 402 Kent, pastureon reclaimed coastal marsh beside the River Swale, where thespecies comprises 73 per cent of the population. This is the onlycensus plot on which passerines (5 species) are outnumbered bynon-passerines (9), which include Lapwing, Partridge, Redshankand Black-headed Gull in addition to riverside birds. The plot 752Somerset (and another in this area) has little cover, since most ofit has been cleared to facilitate mechanical cleaning of the drainagedykes. Some Northern farms show low densities, and this is furtherdiscussed on p. 222.

The most successful farms from the ornithologist's point of vieware not those with the most varied cropping programme, nornecessarily those with the greatest length of hedgerow, though thesefeatures help. The best farms are those showing the greatestfragmentation of the habitat. In addition to hedgerows, often withtall trees along them, they have streams or ditches with coveron the banks, small copses or shelter-belts, pools or disusedmarl-pits, and farmhouses and cottages with small orchards andgardens. In Table II (B) 454 Derbyshire and 053 Suffolk are

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BIRD STUDY

excellent examples of this mosaic type of environment. The former,at Ashbourne, has 61 fields enclosed by nearly 12 miles of hedgerowand woodland-edge (15.7 km. per 100 hectares) and is crossed bya stream. Plot 351 Gloucestershire, at North Nibley, also has 61fields and the equivalent of 20.1 km. of hedgerow and woodland-edge, the most so far recorded on a C.B.C. plot. The farm atWangford, 053 Suffolk, has only 17 fields but their boundaries havemuch tall timber and there are small copses, gardens and patchesof scrub. Hedgerow length per sq. km . is 13 km., the same as on awell-censused Warwickshire farm which, however, lacks any otherform of cover and by comparison carries a moderate population of312 pairs of 27 species.

The kind of hedgerow is important, as shown by Moore, Hooperand Davis. They point out that hawthorn is better than beech orelm, and a well-cared-for hedge is poor compared with a neglectedone which has been allowed to develop outgrowths of blackthornand briar, with a matted field-layer of bramble, nettles, etc. ADorset farm, mainly grass, has averaged 58 warblers of eight speciesover the three years 1964-66, partly because of a riverside situation(Reed and Sedge Warblers), but also because of the characteristictype of hedgerow, designed by the former landowner to encouragegame. This comprises a double-banked row of hawthorns andblackthorns interspersed with tall trees, and separated by a nine-foot ditch, the whole providing an attractive habitat for Blackcap,Garden Warbler, Lesser Whitethroat and Chiffchaff. My own plot,814 Hertfordshire, though much of it is an uninterrupted expanseof barley, with a large Skylark and Corn Bunting population, hasan unusually high density of song-birds because the northernboundary is a dry canal now overgrown with thorns, elder, briar,dogwood, etc., a belt of dense scrub 1 km. in length harbouringnearly half the hedgerow nesters on the farm.

DENSITY IN RELATION TO CROPPING

In order to discover if there is an apparent affinity betweenindividual species and different cropping types, all the farms inthe English Midland, Southern and Eastern counties, Glamorgan,Cheshire, Lancashire and West Yorkshire were divided into twocategories, according to whether 60+ per cent of the cultivated areawas under grass (pasture, leys, fallow), or alternatively grew cerealsand root-crops. There were 32 farms in each category, and thecomparative figures for 22 species are given in Table III.

More than twice the densities of partridges (the two species wereadded together) and Skylarks were found in association with arableland than with grass, and the differences are significant. The onlyother species showing a clear association with arable is the ReedBunting (there are too few records for the Corn Bunting to be sure,though its preference may well be for corn). Wren, Robin, WillowWarbler, Chiffchaff and Chaffinch were commoner on grasslandfarms, but there is no evidence of a preference either way forBlackbird, Dunnock and the other hedgerow birds.

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BIRD COMMUNITY OF FARMLAND

It is possible that mixed and predominantly cereal farmingencourages more of the birds that live on the ground because highcover is afforded without a densely-matted field layer to impedeprogress, but other factors could well be involved. That Skylarksare numerous in association with cereal farms might merely reflecta preference for large open fields, since they are also abundantand widespread on open grassy areas in the Highland Zone. Theassociation with cropping is probably indirect: for example, Wrendensity is probably affected by the frequency of streams and ditcheswith good cover, and that of Chaffinch and Robin by the incidenceof tall unkempt hedges with mature trees; these are conditions mostlikely to be met on grassland farms with stock-proof hedgessurrounding relatively small fields.

An attempt was made to plot the densities of Blackbird, Dunnockand Whitethroat on census plots where the length of hedgerowand woodland-edge was known. Except that there is a definite(and not unexpected) tendency for the upper limit of the first twospecies to advance with increasing length of hedgerow, and for thelatter to do so to a peak at about 12-13 km. per 100 hectares andthen decline (perhaps because of decreasing field-size), nothingtangible emerged from this exercise. Clearly many variables areinvolved, and a multiple regression analysis is being applied to anumber of the more obvious ones and will be reported on in alater paper.

SPECIES DISTRIBUTION ON LOWLAND FARMS

In the Lowland Zone the `field' or `steppe' species (Partridge,Lapwing, Skylark, wagtails) together seldom contribute less thanseven or more than 16 per cent of the whole community. The Swiftand hirundines account for only a few per cent at best, and areusually associated for breeding purposes with villages and hamletsrather than with the farmland. Likewise birds-of-prey and owls,together with other non-passerines, form a very minor part of thecommunity. Thus, over 80 per cent of the normal farmland com-munity is composed of `forest' birds.

Among these the Blackbird is now the dominant species; it ismuch the commonest species of agricultural land (as well as ofrural and suburban gardens) in the lowlands, though not usually inthe Highland Zone (p. 223). It comprises between 10-20 per centof the population. In the sample group of Midlands farms Skylarksvary between 2-18 per cent but Blackbirds are often twice to fourtimes as common; elsewhere, there are a few farms on whichSkylarks do not appear. If one wanted a definition of a farm birdcommunity in the central English lowlands one could say that itis a community in which Blackbird and Skylark occur roughly inthe proportion of two, three or four to one, together making upbetween 15-40 per cent of the population. Other communities inwhich Blackbird is dominant (e.g. parkland, suburban gardens, andsome kinds of woodland) are without Skylarks.

The next most successful farmland species is undoubtedly theDunnock : this is a bird of the woodland edge and all forms of

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scrub rather than of the forest proper, so that the linear scrub ofhedgerows suits it ideally. It takes up between 8-16 per cent of thepasserine total. Robin and Chaffinch, which are more particularly`forest' species, require well-grown hedgerows with trees, and aremore restricted in consequence : either may reach, but will rarelyexceed, 12 per cent of the passerine population. Whitethroat, Linnetand Yellowhammer may register around 10 per cent, with BlueTit and Song Thrush rather less. Great Tit, Wren, Greenfinch (andprobably Starling) only seldom reach seven per cent.

COMPARISONS WITH OTHER REGIONS

Eastern EnglandThe most striking feature of the farms in the Eastern Counties

(Lincolnshire, Cambridgeshire, Norfolk, Suffolk, Essex) is the highgame-bird density—partly because of Pheasant rearing (densities of21 and 13 are recorded in Lincolnshire and Norfolk, and 6-9 arefrequent in the region), but also because of the big contributionmade by the introduced Red-legged Partridge. This species equalsor outnumbers the native one on 77 per cent of the plots, butMiddleton and Huband (1965) believe that this dominance has avery recent history. The censuses in these counties show averagedensities of 6.3 pairs per 100 hectares for Alectoris and 5.7 pairsfor Perdix. The corresponding figures for a wider sweep of adjacentMidland counties, taking in 4,000 hectares as far west as Warwick-shire, Oxfordshire and Berkshire, are 1.0 and 4.4.

It is possible there is a climatic effect, the Red-legged Partridgebeing favoured by weather of a `continental' type (the presentexpansion appears to date from the fine anticyclonic summer of1959, vide Middleton and Huband), for in southeast England thedisparity between winter and summer temperatures and rainfallis greater than elsewhere. According to Voous (1960) the Red-leggedPartridge was formerly commoner and more widespread in WesternEurope: the progressive amelioration since the latter part of thelast century may have adversely affected its status in the maritimecountries, as well as checking its advance in England beyond thosecounties which have retained a climate most nearly approachingcontinentality. It will be interesting to watch the C.B.C. resultsfor any change which may occur now that a climatic recessionappears to be under way: for according to Manley (1964) thedecade 1940-50 was the first period since 1860 when average wintertemperatures fell, in association with less precipitation, while averagetemperatures for other seasons rose—a trend towards increasingcontinentali ty.

The second striking feature (and this also may have a basis inclimate) is the relative commonness of the Turtle Dove in the Eastas compared with the Midlands sample. Over the East Angliansector as outlined above it shows a density of 3.7, while in thecentral Midlands group it barely reaches 0.9. Turtle Doves arefound on 90 per cent of the eastern plots, attaining a density of9-10 pairs on some. The Stockdove too is strongly represented.

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more than half the returns indicating a density of 1-3 pairs, with6-7 on farms in Norfolk and Suffolk.

The occurrence of a network of drainage ditches on some low-lying fen-country farms contributes to high numbers of Mallard(two plots have densities of 5, and two reach 10 and 12) andMoorhen (two with 14) locally. Similarly with the Sedge Warbler,exceptional densities being 12 and 33 pairs.

Skylark numbers are variable as in the Midlands, but highdensities are found on fen reclaimed for arable farming at Bardney,Lincolnshire (67), and on plots in Norfolk (36, 47) and Cambridge-shire (40). Among Corvidae, the scarcity of Magpies is noteworthy :according to Parslow (1967) this is the result of a decline duringthe 1950s. One might be tempted to relate this and the infrequencyof Carrion Crows to persecution contingent upon game-rearing wereit not that the Jay is more strongly represented in the East thanit is elsewhere. It occupied 35 per cent of the 1966 plots and waspresent on over half of all those surveyed during the years 1963-66.Tit numbers are low on the whole, and Yellow Wagtails areextremely scarce compared with the Midland counties.

Some farms record high finch densities : two in Cambridgeshirehave 35 and 27 for Linnet, with good Greenfinch and Goldfinchtotals, as well as 32 and 44 for Yellowhammer. One of these has alarge Corn Bunting (17) and the other an unusual Reed Bunting (14)population. Densities of between 20-30 Tree Sparrows are foundon 30 per cent of the plots.

South and Southwest EnglandThis group comprises the English Channel counties from Kent

west to Cornwall, with the addition of Surrey, Wiltshire andSomerset. It is an unsatisfactory grouping since in some respectsthe bird fauna of the Kent and Sussex farms tends to reflect thatof East Anglia, and shows marked differences from Dorset, Devonand Somerset. For example, Red-legged Partridge (with one ex-ception in Somerset) is noted only from the east, the Jay is strongin these counties but weak in the west, while the Turtle Doverecords are confined to Kent, Sussex and Surrey where 77 per centof the plots have 1-3 pairs, a Thanet plot with 14 being exceptional.Two Isle of Thanet plots, and one in Sussex, report CollaredDoves (2 pairs).

Density figures for most species, especially the commoner ones,fall within the ranges shown for the central Midlands sample.There is a high figure for Skylark (73) on reclaimed coastal marshin Kent 'and the Isle of Thanet densities are good. Wren totals of24-28 occur on rather `wet' farms in Sussex, Dorset and Somerset,and there are good Song Thrush totals (29, 32) on two Sussexfarms. Plot 703 Sussex near Chichester Harbour, crossed by a riverwith reed-beds, has abnormally high densities of Reed (21) andSedge (19) Warblers, but the latter is exceeded by another Sussexplot (32). The first plot also has high densities for Moorhen (29),Mallard (14) and Coot (6), the last being matched by 402 Kent. InHampshire, Dorset and Somerset (but not in the east of the region)

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the Chiffchaff is unusually common on farmland, reaching densitiesof 11-14 (once 20) on four areas; Willow Warblers are scarce bycomparison with the West Midlands and Wales. Redstarts (2-5)are reported on Somerset plots, but there are none in the east;Meadow Pipits and Yellow Wagtails appear on the Kent marshesand at sea-level and 750 feet in Somerset. Two Hampshire plotshave Nightingales as had Surrey and Sussex ones formerly, whilefarms in Sussex, Devon and Cornwall each had a pair of CirlBuntings in the earlier years of the census. Reed Buntings arerather scarce except on 703 Sussex (13) and Tree Sparrow totalsare low.

West Midlands and WalesThese plots comprise Herefordshire (3), Gloucestershire (5),

Glamorgan (3), Radnorshire (2) and Monmouthshire (2). One inHerefordshire, and 351 Gloucestershire, are particularly rich inhedgerows and trees and show unusually high densities for anumber of species, including Robin (57, 53), Whitethroat (35, 23),Dunnock (49, 26) and Chaffinch (56, 49).

Otherwise the main differences from the central Midlands sampleconcern distribution rather than density. There is a better represen-tation for Stockdove (on 40 per cent of the plots), Little Owl (60per cent), Long-tailed Tit (53 per cent) and Wren (all plots), togive the most marked examples. Also the Redstart, very scarce inthe Midlands sample, is a prominent farmland bird in the West,being found on 53 per cent of the returns at a density of usually1-3, but exceptionally 9-10. Meadow Pipit too comes into thepicture, occurring on a third of the census areas, with a densityreaching 6 on a Radnorshire farm and 12 on one in Herefordshire.The appearance of Pied Flycatcher (5) on a Radnorshire farm isexceptional and due to the provision of nest-boxes.

Willow Warbler representation is similar to the Midlands but thenumbers are much higher with densities ranging from 6-26. Thenumbers of Skylark are low on the whole, especially in theCotswolds, where two farms (including plot 351, mentioned above)are without any. Reed Bunting and Tree Sparrow are poorly repre-sented, and the Corn Bunting is absent from the returns.

Northern EnglandPlots in the north exhibit a high proportion of the `field' or

`steppe' species. Curlew and Snipe occur regularly (density 1-6)alongside the Lapwing, and other possibilities are indicated by thetally at Ryehill in Northumberland—Mallard, Partridge, Pheasant,Moorhen, Oystercatcher (2), Ringed Plover (3), Common Sandpiper(3) and Redshank (2), with Teal and Goosander in previous years.At 712 West Yorkshire, a pair of Golden Plovers nested in 1965:here Lapwings have averaged 31 pairs since censusing began in1963, while a Lancashire `moss' farm near Leigh has a density of15. However, Lapwing numbers appear to have declined in theNorth as well as in the Lowlands : only two pairs remain on aWestmorland plot which carried 22 pairs in 1962. The failure of

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the bird to make good the losses it sustained during the hard winterof 1962-63 is a cause of considerable anxiety.

Meadow Pipit, Yellow Wagtail and Corn Bunting share with theSkylark the niche for ground-nesting passerines : apart from anexceptional 14 on the farm at Ashbourne, 454 Derbyshire, the TreePipit is scarce. The Skylark is the commonest song-bird on Northernfarms, the usual density being 14-30 and the 16 plots giving anaverage of 21 pairs. Comparable figures for the Blackbird are 3-25and the average of 19 is inflated by an exceptional density of 65 atAshbourne. On farms in Pennine country Wren, Blackbird, Robin,Dunnock and Whitethroat show poor totals. The Willow Warbler,with densities up to 13 and 18 (but 53 at Ashbourne), takes overfrom the Whitethroat as the commonest summer visitor. MeadowPipits occur on 44 per cent of the plots, density to 19, and YellowWagtails on 38 per cent, density to 7.

The relative paucity of the lowland hedgerow species is partlycompensated by a greater variety of passerines. There are Wheatear(1-3) and Whinchat (1-4) each on three plots, while Lesser Redpoll(1-5) occurs on five : Redstarts are found on six (1-7), on four ofwhich they equal or outnumber Robins. Tit densities are low.Chaffinch and Greenfinch are the commonest finches, with Linnetregular but at low density, usually 1-7. Goldfinch and Bullfinch,Lesser Whitethroat and Chiffchaff are extremely scarce, whileGarden Warbler is rather more frequent than Blackcap.

Details of some of the Pennine country farms are given in TableII. At Ryehill, Northumberland (350 feet), there is a rich bird-faunacomprising 259 pairs of 40 species, while another at a moderatealtitude near Appleby, Westmorland, has 35 species though only151 pairs. Compare with these the highest plots-056 Cheshire at1,000 feet with 28 species, 106 pairs; and 712 West Yorkshire at900 feet with 20 species, 133 pairs. Although the species varietydeclines with altitude, overall density does not appear to decreaseproportionately.

Tantalisingly few upland returns are available for study, and onecould wish for many more. Variation within much wider limits thanin the Midlands is to be expected in the Highland Zone, sinceclimatic characteristics are subject to much more rapid change withaltitude in the British Isles than in other temperate countries. Thetree-line is unusually low compared with the rest of Europe, owingto greater exposure to strong Atlantic winds and the generallycooler and cloudier summers. This sets the upper limit of settlementwith unimproved farmland at a little over 1,500 feet. As altitudeincreases, the length of the growing season declines sharply: anexample may be quoted from Manley (1952), who records thatNenthead in Cumberland, with pasture ranging from 1,500-1,800feet, has a growing season ten weeks shorter than in the lowlands.

Moreover, the fall in average temperature with height is mostmarked in the spring, especially in May, when birds on low ground

2That portion of the year during which the mean temperature at the grassroots exceeds 6° C. (43° F.), the minimum for the active growth of crops.

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are already well advanced in their breeding cycle. At Malham Tarnin the West Riding (1,200 feet) in the last week of May 1966 wefound that the nesting of Chaffinch, Song Thrush and other specieswas at least three weeks behind the lowland Midland schedule.During the cold, wet spring of 1967 it was even later. Of moreimportance perhaps than the actual length of the growing season isthe rapid falling-off with height in the intensity of `accumulatedwarmth'—i.e. the amount by which the mean temperature exceeds6° C.—for this affects not only the yield of crops and maturingof vegetation, but also the availability of insect food. Manley, whodiscusses these climatic effects in some detail, shows also that theinfluence of seasonal variations becomes more pronounced withaltitude. Cool, cloudy summers may be disastrous, but warmanticyclonic weather brings much greater benefits to the hills thanto the low ground.

One would expect as a corollary of this complicated and poten-tially changeable climatic environment a more marked response inthe bird fauna to factors of shelter and aspect, as well as short andlong-term shifts where marginal conditions of habitat prevail. It ispossible that bird populations in such marginal areas, even atmoderate elevations in the Highland Zone, are boosted by popula-tion pressure from more suitable lowland haunts following a suc-cession of good breeding seasons and mild winters; and thatconversely they are deprived for a period of years after a severewinter whilst the available vacancies are being filled on lowerground. Some such effect is suggested at 711 North Yorkshire whereno fewer than nine species (including Little Owl, Blue Tit, SongThrush, Chaffinch and Yellowhammer) have nested sporadically inone or other of the four census years 1963-66; and at 712 WestYorkshire, where occasional nesters in earlier years have includedGreat Tit, Mistle Thrush, Robin and Little Owl.

Much more census data are needed before conclusions can bedrawn, but it seems likely that the farm bird-community even atmoderate levels in the North and West is in a much more fluidstate than under the more stable climatic conditions whichcharacterise the Lowland Zone.

ACKNOWLEDGEMENTS

This study is based on field-work which has been assiduously conducted bywell over a hundred participants in the B.T.O. Common Birds Census. It isnot possible to acknowledge them all by name, but the Trust's gratitude fortheir continued diligence and support is no less on that account. In addition,my thanks are due to a number of colleagues who read and criticised thispaper at various stages—R. K. Murton, R. C. Homes, N, W. Moore, M. D.Hooper, and D. W. Snow. I am particularly grateful to Roger S. Bailey forhelp with the statistics.

SUMMARY

Since agricultural land embraces 80 per cent of England and Wales it mustbe considered the most extensive bird habitat in the countryside. Its mainfeature is a complex hedgerow system that is not more than 200-300 yearsold. The expansion of the human population, and current trends in farmingpractice, are eroding this habitat to an increasing degree.

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The composition of a 'typical' English lowland farm bird community at thepresent day is examined by analysing 28 returns from Common Birds Censusplots, totalling 2,200 hectares, in the central Midlands. The incidence anddensities of 58 species on this group of farms are given in Table I. Overthe country as a whole, low densities and poor species representation arefound in relatively uniform environments (e.g. reclaimed fen and coastalmarsh), while the densities of species and pairs can be four times as greatwhere the habitat is most diversified (Table II). The influence of length andvariety of hedgerow cover, and of cropping type, is discussed.

The Blackbird is the dominant farmland species in the central EnglishLowlands, usually with Skylark and Dunnock subdominant. Robin and Chaffinchfollow, rarely exceeding 12 per cent of the passerine population.

A comparison of the incidence and densities of various species is madebetween the central Midlands sample group and groups of census plotsrepresenting Eastern England, South and Southwest England, West Midlandsand Wales, and Northern England. Some of the striking differences noted arethought to be due in part to climatic factors.

REFERENCES

ANON. 1966. The Structure of Agriculture. (Ministry of Agriculture, Fisheriesand Food). H.M.S.O. London.

BAILEY, R. s. 1967. An index of bird population changes on farmland. BirdStudy, 14: 195-209.

CORNWALLIS, R. K. (in press). Change on the farm.MANLEY, G. 1952. Climate and the British Scene. London.MANLEY, G. 1964. The evolution of the climatic environment. In J. W. Watson

and J. B. Sissons, The British Isles—a Systematic Geography. London.MIDDLETON, A. D. and HUBAND, P. 1965. Increase in Red-legged Partridges

(Alectoris rufa). Game Research Assoc. 5th Anual Rep., 14-25.MOORE, N. W., HOOPER, M. D. and DAVIS, B. N. K. 1967. Hedges: 1, Introduction

and reconnaissance studies. J. Appl. Ecol., 4:201-220.PARSLOW, I. L. F. 1967. Changes in status among breeding birds in Britain and

Ireland. Brit. Birds, 60:2-47, 177-202, 261-285.mow, D. w. 1965. The relation between census results and the breeding

population of birds on farmland. Bird Study, 12:287-304.voous, K. H. 1960. Atlas of European Birds. London.

The scientificgiven below:

MallardTealGoosanderRed-legged

PartridgeGrey PartridgePheasantMoorhenCootOystercatcher

LapwingRinged PloverGolden PloverCommon SnipeCurlewCommon SandpiperRedshankStock DoveWoodpigeonTurtle Dove

Anas platyrhynchosA. creccaMergus merganserAlectoris rufa

Perdix perdixPhasianus colchicusGallinula chloropusFulica atraHaematopus

ostralegusVanellus vanellusCharadriushiaticulaC. apricariusCapella gallinagoNumenius arquataTringa hypoleucosT. totanusColumba oenasC. palumbusStreptopelia turtur

Collared DoveCuckooLittle OwlTawny OwlSwiftGreen WoodpeckerSkylarkHirundines

Carrion CrowRookJackdawMagpieJayGreat TitBlue TitCoal TitMarsh TitWillow TitLong-tailed Tit

and tables are

S. decaoctoCuculus canon'sAthene noctuaStrix alucoApus apusPicus viridisAlauda arvensisHirundo rusticaDelichon urbicaRiparia ripariaCorvus coroneC. frugilegusC. monedulaPica picaGarrulus glandariusPants majorP. caeruleusP. aterP. palustrisP. montanusAegithalos caudatus

c

APPENDIX

names of the species mentioned in the text

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TreecreeperWrenMistle ThrushSong ThrushBlackbirdWheatearWhinchatRedstartNightingale

RobinReed Warbler

Sedge WarblerBlackcapGarden WarblerWhitethroatLesser WhitethroatWillow Warbler

Chiffchaff

Certhia familiarisT. troglodytesTurdus viscivorusT. philomelosT. merulaO. oenantheSaxicola rubetraP. phoenicurusLuscinia

megarhynchaErithacus rubeculaAcrocephalus

scirpaceusA. schoenobaenusSylvia atricapillaS. borinS. communisS. currucaPhylloscopus

trochilusP. collybita

Spotted FlycatcherPied FlycatcherDunnockMeadow PipitTree PipitPied WagtailYellow WagtailStarlingGreenfinchGoldfinchLinnetRedpollBullfinchChaffinchYellowhammerCorn BuntingCirl BuntingReed BuntingHouse SparrowTree Sparrow

Muscicapa striataM. hypoleucaPrunella modularisAnthus pratensisA. trivialisMotacilla albaM. flavaSturnus vulgarisChloris chlorisCarduelis carduelisC. cannabinaC. fíammeaPyrrhula pyrrhulaFringilla coelebsEmberiza citrinellaE. calandraE. cirlusE. schoeniclusPasser domesticusP. montanus

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