Breeding Bird Species Diversity in Relation to Increasing Urbanisation

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1 Bird Study ISSN: (Print) (Online) Journal homepage: Breeding Bird Species Diversity in Relation to Increasing Urbanisation L. A. Batten To cite this article: L. A. Batten (1972) Breeding Bird Species Diversity in Relation to Increasing Urbanisation, Bird Study, 19:3, , DOI: / To link to this article: Published online: 23 Jun Submit your article to this journal Article views: 1564 Citing articles: 40 View citing articles Full Terms & Conditions of access and use can be found at

2 Breeding Bird Species Diversity in Relation to Increasing Urbanisation by L. A. Batten The vicinity of the Brent Reservoir (Middlesex) has undergone extensive urbanisation during the last 140 years. The area has received a great deal of attention from ornithologists throughout this period and their observations have enabled the author to make a study of the changes in the bird life which took place as London spread outwards and eventually engulfed the area. THIS PAPER PRESENTS the results of an investigation into the changing bird-life of an area of northwest London surrounding the Brent Reservoir during the course of its urbanisation. The study area is located six to seven miles northwest of Marble Arch and is bounded on the south side by the North Circular Road, on the east by the Watford Way and Hendon Way; Kingsbury Road forms the northern limit, while the western perimeter follows Neasden Lane, Forty Lane and then the Bakerloo electric railway to Kingsbury. The area covers 817 hectares (2,018 acres), the highest point being Barn Hill at 282 feet. From here the land slopes away to 100 feet on the banks of the Brent Reservoir, and again rises to just over 200 feet in the northeast corner of the area. The ground in the centre also rises to 200 feet so that the whole area takes on the form of a shallow bowl raised at the centre. The area is ideal for a study of this nature because ever since the reservoir was constructed in 1833 there has always been at least one ornithologist working there. An almost complete qualitative history of the bird-life over nearly 140 years is now available in the literature. URBANISATION OF THE AREA At the beginning of the period the natural-banked reservoir was a rural beauty spot surrounded by mixed farmland with scattered copses, overlooked by the wooded height of Barn Hill. Little change in land use occurred until the 1890s when rows of houses were built close to the northern end of the reservoir. By 1913 urbanisation had got under way and 10% of the land surface had been built on, mainly towards the north and east of the reservoir. Further developments took place in the 1920s when the North Circular Road was constructed, and by % of the area was built up. The gradual increase in urbanisation is illustrated in Figure 1 which shows the area at intervals since Major alterations are now taking place as new high density housing estates replace luxurious houses with large well-wooded gardens. Further changes are envisaged and the degree of urbanisation is likely to increase although under present policies it is unlikely ever to reach 100%. 157

3 BIRD STUDY At the present time there are nine main habitats. The 817 hectares can be broken down as follows: houses and factories hectares (1,310 acres), the farm at Barn Hill 97.1 hectares (240 acres), open water 50.6 hectares (125 acres), playing fields 52.2 hectares (129 acres), scrubby ground 36.4 hectares (90 acres), allotments 17.8 hectares (44 acres), reed swamp and shallow water 13.3 hectares (33 acres), parkland 11.7 hectares (29 acres) and fmally a rubbish dump 7.2 hectares (18 acres). As a result of man's influence there is surprisingly more diversification of the environment than there was in 1877 when the main habitats consisted of farmland, homestead, stony downland, wood and scrub, open water and reed swamp. Figure 1. The study area at intervals from with the built-up parts in black. 158

4 BIRD DIVERSITY AND URBANISATION CHANGES IN BREEDING BIRDS SINCE 1833 In any area of land one must expect changes in the composition of breeding species over as long a period as 140 years. Some of these changes will be due to extrinsic factors such as variations in climate or modifications to the area itself. Other intrinsic differences may be caused by long term and widespread population changes in the birds themselves. It is often difficult to be sure which of these factors is responsible for changes in status of certain species, particularly as there is a possibility that suburban habitats may be second-rate for some species, and occupied only in years of high population level. Long term population fluctuations which might occur nationally or internationally and go unnoticed elsewhere could be accentuated in this sort of area. Although no quantitative data exist, there is evidence based on presence or absence that the Green and Great Spotted Woodpeckers have fluctuated markedly in the last 140 years; they were described as common in the early decades of the nineteenth century, were rare in the latter half, and common again by the 1920s. They have been declining since the middle 1950s (see Figure 2). The first oscillation occurred when the area was changing little, in fact the Green Woodpecker was absent as a breeding bird for some 30 years and the Great Spotted Woodpecker for nearly 40 years. The present decrease could at least be partly due to land use changes since Parslow (1967) states there is no evidence of a marked general change in recent years. During the period under consideration a number of other species have fluctuated in such a way as to show a return to a former status after a period of scarcity or abundance. The most noticeable of these are Coot, Stock Dove, Nuthatch, Goldfinch, Bullfinch, Redpoll, jay and Magpie. Figure 2 illustrates these fluctuations in relation to a time scale. As some of these population changes took place when the area was not being extensively urbanised it seems likely that other factors were largely responsible for the early fluctuations. Other species such as Grey Wagtail, Reed Warbler, Nightjar, Pheasant, Tree Pipit and Cirl Bunting may have been affected similarly. Red-legged Partridge and Little Owl have also had a period of regular breeding in the area but these were both species introduced into the country in the nineteenth century. A number of species declined and disappeared as breeding species fairly rapidly by the end of the first decade of the present century. Although only about 10% of the land was urbanised by then, the surrounding districts nearer London were being developed and with this came the inevitable increase in disturbance from the human population. Some species lost to the area at that time were high forest species which appear not to be able to tolerate human disturbance. Hawfmch, Redstart and Wood Warbler are in this category. The Kingfisher suffered as a result of the increased pollution of the rivers and tributaries in the area. The Lapwing and Corncrake were also lost and it is likely the former went because of the continual plunder of its eggs. The decline of the Corncrake is a mystery, and the loss of Goldcrest and Nightingale seems premature. On the credit side the Great Crested Grebe appeared, presumably helped by the Bird Protection Act of 1880 which banned its slaughter to adorn Victorian ladies' hats. This fashion did not die out until about The Coot also reappeared but at the time of writing there are signs of a decreasing breeding population and an extremely poor productivity rate at the reservoir, so this species may once again disappear as a breeding bird in the not too distant future. 159

5 r it 11/,71///...i,, STOCK DOVE l / 4 il, 1,, Ill I 11111,..0 ' 111//11,',1,1/1/ 18,014; ''.11, /2"11//u v 1111/111111, Ill ill. / I I GREEN WOODPECKER by //, /1, 777/,/ ' '/ I r :/// i I /0/ / ' GREAT SPOTTED WOODPECKER j///7/7 / M ' ////q/ /.///, ///.,, /,../ // /,/,// ;, ; 7/i ' NUTHATCH / r ////://c//' '''//// /1111/1111/11///1701 GOLDFINCH, i / ii, 1,/ /1,1,,,,1 1 11/11 ' Vil 1 111/ / /11/21//1 11/1/1.:/;141, / IA LESSER REDPOLL,, /,,, //f4 /07 BULLFINCH f AV/ i 1 / /, ///,/// / // 1 1//7//,/,//// '/. i /// / MAGPIE,, 7//// /////i/ / ///7/////////////// JACKDAW - / /// 7/ ////// / / / ///////// 1///7/ 1 /f/i7//// /4. 'il:///// ' i, " i 177w I/ 7 I 1/,' /'; '','",!I f,' 1, ,11117' II/IIII/ ' II.11/1/111 / /// / 7,I.' /I/ 14 II/ I I I I/ II I I I 1 11/?1/1111 I // %1/1/1/1 / ' ' 7/ 111/1 I /11/111, /A1111/11/ (ill"

6 BIRD DIVERSITY AND URBANISATION FIGURE 3 Changes in breeding species from 1830 to breeding or holding territory regularly (B). breeding or holding territory occasionally (b). regularly present in the breeding season but not apparently holding territory (P) present occasionally in the breeding season but not apparently holding territory (p). Species Little Grebe Podiceps ruficollis Great Crested Grebe Podiceps cristatus Grey Heron -00 Ardea cinerea Mute Swan Cygnus olor Mallard Anas platyrhynchos Gadwall -00 Anas strepera Tufted Duck Aythya fuligula Sparrow Hawk Accipiter nisus Kestrel Falco tinnunculus Red-legged Partridge Alectoris rufa Partridge Perdix perdix Pheasant Phasianus colchicus Water Rail - Rallus aquaticus Corncrake Crex crex Moorhen Gallinula chloropus Coot Fulica atra Lapwing Vanellus vanellus Stock Dove Columba oenas Woodpigeon Columba palumbus Turtle Dove Streptopelia turtur Cuckoo 0 Cuculus canorus Barn Owl Tyto alba Long-eared Owl Ado otus Little Owl Anthene noctua Figure 2 (opposite). 'Long term' population changes for selected species (see Figure 3 for definition of symbols). 161

7 BIRD STUDY Species Tawny Owl Strix aluco Nightjar Caprimulgus europanis Swift Apus apus Kingfisher Alcedo atthis Wryneck _lynx torquilla Green Woodpecker Picus viridis Great Spotted Woodpecker 0 Dendrocopos major Lesser-Spotted Woodpecker Dendrocopos minor Woodlark Lullula arborea Skylark Alauda arvensis Swallow Hirundo rustica House Martin Delichon urbica Tree Pipit Ant hus trivialis Meadow Pipit Ant hus pratensis Yellow Wagtail Motacilla flava Grey Wagtail Motacilla cinerea Pied Wagtail Motacilla alba Red-backed Shrike Lanius collurio Wren Troglodytes troglodytes Dunnock Prunella modularis Grasshopper Warbler Locust ella naevia Sedge Warbler Acrocephalus schoenobaenus Reed Warbler Acrocephalus scirpaceus Blackcap Sylvia atricapilla Garden Warbler Sylvia born Whitethroat Sylvia communis Lesser Whitethroat Sylvia curruca Willow Warbler Phylloscopus trochilus Chiffchaff Phylloscopus collybita 162

8 BIRD DIVERSITY AND URBANISATION Species Wood Warbler Phylloscopus sibilatrix Goldcrest Regulus regulus Spotted Flycatcher Muscicapa striata Whinchat Saxicola rubetra Stonechat Saxicola torquata Wheatear Oenanthe oenanthe Redstart Phoeni tutus phoenicurus Robin Erithacus rubecula Nightingale Luscinia megarhynchos Blackbird Turdus merula Song Thrush Turdus philomelos Mistle Thrush Turdus viscivorus Long-tailed Tit Aegithalos caudatus Marsh Tit/ Willow Tit* Parus palustrislmontanus Coal Tit Parus ater Blue Tit Parus caeruleus Great Tit Parus major Nuthatch Sitta europaea Treecreeper Certhia familiaris Corn Bunting 0 Emberiza calandra Yellowhammer Emberiza citrinella Cirl Bunting Emberiza cirlus Reed Bunting Emberiza schoeniclus Chaffinch Fringilla coelebs Greenfmch Carduelis chloris Goldfinch Carduelis carduelis Linnet Acanthis cannabina Redpoll Acanthis flammea Bullfinch Pyrrhula pyrrhula 163

9 BIRD STUDY Species Hawfinch Coccothraustes coccothraustes House Sparrow Passer domesticus Tree Sparrow Passer montanus Starling Sturnus vulgaris Jay Garrulus glandarius Magpie Pica pica Jackdaw Corvus monedula Rook Corvus frugilegus Carrion Crow Corvus corone Total B** Total B-Eb Total B+b-FP Total B-Eb+P-Fp *Willow Tit has been the only one present since Earlier records of Marsh Tits may well refer to Willow Tits. **A species is considered to belong to this category if it bred or held territory in at least ten years of the 20-year period concerned. Of the breeding species which have been lost to the area at least for the time being nearly 60% have declined nationally (Parslow 1967) and this probably has contributed to their disappearance. This leaves Turtle Dove, all three woodpeckers, Kingfisher, Swallow, Meadow Pipit, Wood Warbler, Nightingale, Long-tailed Tit, Nuthatch, Treecreeper, Goldcrest, Hawfinch and Jackdaw which are presumably victims of the changes inflicted by urbanisation. It is clear that the number of species present in the breeding season has decreased as the area has become increasingly built up. Figure 4 illustrates this graphically. Although the total number of species regularly breeding has dropped from 72 to 43, only 37 of the species which bred before 1860 still do so. This means that six regular breeding species have been gained Little Grebe, Mute Swan, Tawny Owl, Magpie, Swift and Tree Sparrow. In addition to this a further three species are now recorded as occasional breeders but were unknown as such before These are Great Crested Grebe, Tufted Duck and Grey Wagtail. Detailed information on species present in each breeding season since 1957 is available. During this time the area has been in a state of 60-65% urbanisation. There is considerable variation in the actual species involved each year. For example, out of 52 which bred in at least one of the years only 25 (48%) bred every year; and out of the 66 species which were observed in at least one breeding season only 37 were seen in all the years concerned. It would seem therefore that the breeding avifauna of this urbanised area contains a very large proportion of irregular breeders. This principle has also been found to occur in other habitats. For example, on a farm in 164

10 BIRD DIVERSITY AND URBANISATION Suffolk which has been censused for eight years 64% of the species occurring were regular breeders, and another farm in Westmorland censused for 10 years had only 52% of its species in this category (Benson and Williamson, 1972; Robson and Williamson, in press). So far the area has only reached the stage of 65% urbanisation and at the present rate of increase it will be a very long time before total urbanisation occurs, if it ever does. An attempt was made to predict the number of breeding species which would remain when that hypothetical stage was reached, by examining a part of the study area which was already fully developed; 24 species were found breeding at this stage, but only 20 of these were regular. When this point is added to Figure 4 the resultant series of points suggests a fairly uniform decline in species diversity with increasing urbanisation. The effect of development could even be beneficial up to the first 10% because new habitat is created, allowing the Swift to become a regular breeding B+b NO. OF SPECIES B+b +P B+b+P+p % URBANISATION Figure 4. The number of species resident in the summer in relation to the increase in urbanisation (see Figure 3 for definition of symbols). 165

11 BIRD STUDY species. At the other end of the scale the decline tails off to 20 species; however, these are present in an area containing houses with gardens. Preliminary observations were made on a new high density housing estate containing over 370 people to the hectare, with no gardens, merely lawns and a few trees. The breeding avifauna was restricted to seven species; Woodpigeon, Blackbird, Blue Tit, House Sparrow, Starling and Carrion Crow. In addition the Feral Pigeon was also found to be colonising. SUMMARY The diversity of species breeding or present in the breeding season in an area in north London is reviewed at intervals since 1830 and the rate of decrease with increasing urbanisation is measured. The number of species breeding regularly when the area was less than 1% urbanised varied from 67 to 72; but was 71 at 10%, 64 at 30%, 53 at 50% and 43 at 65% urbanisation. An attempt to predict the number of species breeding at 100% urbanisation from part of the area now completely developed revealed 20 species. There is considerable variation in the actual species involved in this suburban environment. Out of the 52 species which bred in at least one of the years only 25 bred every year. ACKNOWLEDGEMENTS I would like to thank Professor E. H. Warmington for his very valuable notes on the birds of the area in the 1920s-1950s; also Mrs Gwen Bonham for typing the manuscript and Mr Kenneth Williamson, Mr C. J. Mead and Mr D. I. Sales for their comments on the paper. I am also very grateful to Mr Paul Moxey, editor of the London Naturalist, for allowing me to use some of the text and figures of an early paper of mine published in that journal. REFERENCES BATTEN, L. A The past and present bird life of the Brent Reservoir and its vicinity. Lond. Nat. 50:8-62. BENSON, G. B. G. & K. WILLIAMSON Breeding birds of a mixed farm in Suffolk. Bird Study, 19: BOND, P Note on the arrival of summer birds at Kingsbury, Middlesex. Zool. for 1844, DIXON, C The Bird-life of London. London. GLEGG, W. E A History of the Birds of Middlesex. London. DARTING, J. E The Birds of Middlesex. London. HOMES, R. C. et al The Birds of the London Area since London. KENDALL, W. B The Birds of Willesden (unpublished MS in Willesden Public Library). LONDON NATURAL HISTORY SOCIETY Lond. Nat. nos LONDON NATURAL HISTORY SOCIETY et seq. Lond. Bird Rep. nos READ, It. II The birds of the Lower Brent Valley (reprinted from Rep. and Trans. Ealing Nat. Science Soc. for 1896). RossoN, R. w. & K. WILLIAMSON (in press). Breeding birds of a Westmorland farm. Bird Study. L. A. Batten, Populations Section, British Trust for Ornithology, Beech Grove, Tring, Hertfordshire. 166