VOL. LI1 MAY No. s 1959 BRITISH BIRDS SURVEY OF HOUSE MARTIN COLONIES IN EAST LANCASHIRE By L. E. BOULDIN INTRODUCTION IN THE SUMMER of 1958, the East Lancashire Ornithologists' Club carried out a local survey of the nesting-sites of the House Martin (Delichon urbica), with a view to ascertaining- their distribution and the factors controlling it. The area chosen for study was that bounded by a circle of 15 miles radius from the centre of Accrington (Fig. 1). This area intrudes into Yorkshire as far as Slaidburn and Paythorne in the north, and to Hebden Bridge in the east. Running roughly south­ west to north-east across the centre of it is the industrial belt Blackburn/Accrington/Burnley/Nelson/Colne, which lies mainly in the valley of the River Calder. To the north-west of Nelson and Burnley the mass of Pendle Hill (1,831ft.) obtrudes between this industrial belt and the Ribble Valley (Longridge/Ribchester/ Clitheroe/Gisburn/Skipton), which in turn gives on to rising moor­ land (LongridgeFell/Easington Fell) and the Hodder Valley around Slaidburn in the north. Much of the eastern and southern parts encroach on high and bleak moorland (Stanbury Moor/Wadsworth Moor/ Heptonstall Moor) in the east and the so-called Forest of Rossendale in the south. The whole is a largely moorland zone embracing a central industrial belt, with minor townships in the north and south, and intersected by a number of prominent river valleys with their accompanying roads, railways and built-up areas. The Leeds and Liverpool Canal also runs diagonally across the area through the industrial belt. Woodland is scarce, but there are some 40 reservoirs, the majority south of the industrial belt. The whole area embraces some 452,000 acres in north-east Lancashire and the overspill into Yorkshire. Individual returns showed that the part east of the Clitheroe/ Whalley environs and north of Ramsbottom in the south had been well covered, but unfortunately little information was received for 141 142 BRITISH BIRDS [VOL. LII FIG. I—SURVEY OF HOUSE MARTINS (Delichon urbica): MAP OF TOWNS AND OTHER PLACE-NAMES IN TEXT The dotted line shows the boundary of the area of the survey: a circle of 15 miles radius from the centre of Accrington, Lancashire. Other lines are main roads. the western half of the area, records of only six sites coming to hand. Thus the value of this survey has been limited by lack of full coverage over the whole of the area chosen for study, but it is possible to assess results from the returns for the eastern half of the area north of a line Hebden Bridge/Todmorden/Rams- bottom. Apart from the wet summer which may have restricted observations and which doubtless had some effect on breeding, the only other factor which should be mentioned is the possible tendency for observers to have concentrated on the various built- up areas in the valleys to the exclusion of outlying hamlets and farmsteads, but many remote rural areas were fully covered, some with negative results. PREVIOUS WORK So far as can be ascertained, this is the first large-scale survey VOL. LII] LANCASHIRE HOUSE MARTIN SURVEY 143 of House Martin colonies carried out in East Lancashire, but there have been previous studies in other parts of the country with which this one may be compared. Hurrell (1930) organized a survey of House Martins in Devon and Cornwall. Then a census was carried out in the Oxford area in 1931 and 1932 (Alexander, 1933), and in the next year (Cramp and Ward, 1934) there was a similar study for the Manchester area. The national sample census of Swallows (Hirundo rustica) in 1934 and 1935 (Boyd, 1935, 1936) included some data on House Martins, and finally there was a sample census in 1949 of Swifts (Apus apus), Swallows and House Martins in certain parts of London (Cramp, 1950). NUMBERS OF BREEDING PAIRS A total of 486 nests were located in 122 colonies, nearly a quarter of which consisted of isolated single nests; this gives an average of a fraction under 4 (3.98) nests per colony. The largest colony contained 31 nests on two adjacent farm buildings at Whiteacre (Map Ref. 612402). The numbers of nests per colony are set out in Table I. TABLE I—SIZES OF COLONIES OF HOUSE MARTINS (DeHchon urbica) IN EAST LANCASHIRE IN 1958 No. of nests per colony 1 2 3 4 5 6 7 8 9 10 11 12 13 14 21 31 No. of colonies 28 31 19 16 5 3 3 3 3 3 o 3 o 3 1 1 Thus over three-quarters of the colonies were of from 1 to 4 nests, though much larger groups occurred. The site with 21 nests was suburban and that with 31 nests was rural. DENSITY The density of nests for the whole of the study area (452,000 acres) was found to be only 1.08 per 1,000 acres. All but 71 of the nests, however, were located in the greater eastern section of the study area which included the Clitheroe, Whalley and Wadd- ington environs and totalled approximately 333,000 acres: in this part the density figure averaged 1.25 nests per 1,000 acres. Further, by map-plotting nests in this eastern section it became obvious that most were located in five main zones, i.e.: — (A) South -east of Burnley. (B) South, west and north of Nelson. (C) North and south of Rawtenstall and Halsingden. (D) Between Whalley and Sabden in the south of the area, and Waddington and Grindleton in the north. (E) In the arc Colne/Salterforth/Barnoldswick/Gisburn/ Bolton-by-Bowland in the north-east. Records for these five main zones are shown in Table II. 144 BRITISH BIRDS [VOL. HI TABLE II—COLONY-SIZE AND DENSITY OF HOUSE MARTINS (Delichon urbica) IN FIVE ZONES OF EAST LANCASHIRE IN 1958 The zones are detailed in the preceding paragraph (see also Fig. i). Approx. No. of No. of Av. nests Density per Area acreage colonies nests per colony 1,000 acres A 5.000 16 65 4.06 13.0 B 3,000 25 112 4.48 37-3 C 10,500 19 52 2.74 4-94 D 13.500 27 87 3.22 6.46 E 18,000 14 52 3-72 2-9 50,000 101 368 3-64 7-36 GENERAL DISTRIBUTION That the House Martin is a suburban rather than an urban or rural breeding species has been well illustrated in previous surveys and is generally confirmed in the present study. Cramp and Ward (1934) and Oakes (1953) recorded the species as decreasing as an urban nester in the Manchester area. Cramp (1950) found the bird absent from Central London and his density figures for the inner suburbs were over 15 times greater than those for the outer suburbs which in turn were nearly twice those for the outskirts. Alexander (1933) for Oxford, found there were three times as many nests in urban and suburban areas as in rural. The plotted results of the present survey indicated clearly that the greatest concentrations of colonies occurred in the suburbs of the large towns, while the species was mostly absent from their centres. On the other hand, there were thriving colonies in purely rural areas, in which category, however, such small centres of human population as Whalley, Waddington, Grindleton, Gisburn and Bolton-by-Bowland, somewhat remote from the large industrial towns, are included. For the whole of the study area it was found that only 4 colonies (8 nests) were strictly urban, 60 colonies (224 nests) were suburban and 58 colonies (254 nests) were rural. It will be noticed there is no marked difference between suburban and rural totals, but this is due to the great size of the rural area included. The totals show that, while most colonies were suburban in location, these tended to contain less nests than those in rural areas, i.e. 3.73 nests per suburban colony as against 4.38 per rural colony. DIRECTIONS FACED BY NESTS Aspects were recorded for 448 of the 486 nests; 193 of these faced from south to west, 145 from west to north, 157 from north to east, and 135 from east to south (the sum of these four figures exceeds the total number of nests because in each case, for reasons of convenience, both the limiting directions of the 90° arc have been included: in other words, the number of nests facing due west VOL. LII] LANCASHIRE HOUSE MARTIN SURVEY 145 is included in both the south-to-west and the west-to-north totals). In more detail, most nests faced south (63), south-west (52), north­ east (51), west (48), east (43) and north (28). Thus it seems, that direction has little significance and it is thought that the slight bias in favour of the south-to-west quarter is probably as much a reflection of the general direction faced by houses as of any preference on the part of the birds. By comparison, Hurrell (1930) found that 44 of 65 nests in Cornwall faced south, and that all of 126 nests in Devon looked south, south-east or south-west. FRONTS, SIDES OR BACKS OF BUILDINGS Particulars of the position of the wall concerned were given for 451 of the 486 nests, and 342 (75.8%) of these were at the fronts of buildings while 87 were at the sides and only 22 at the backs. Thus there were 3! times as many nests at fronts as at sides and backs together.