CHANGES IN THE STATUS OF HEATH AND MARSHLAND BREEDING BIRDS IN THE WALBERSWICK AREA, 1953-72 D . J . PEARSON
THE extensive areas of heath and marshland which formerly existed near the East Suffolk coast have become greatly reduced over the past twenty years, with accompanying changes in the status of many breeding birds. One of the areas least affected has been that centred about Westwood Marsh, beUveen the villages of Walberswick, Blythburgh, and Dunwich. Despite loss of much of the original heathland for forestry planting and agricultural use, a variety of natural habitats still exists within this area, and it now constitutes one of the main East Suffolk breeding strongholds of a number of species which have disappeared or become scarce elsewhere. The area still includes many acres of heathland, open pine, birch and oak woodland as well as large areas of reedbed and salt marsh. The main habitat changes since 1952 have been those associated with the drastic decline in rabbit numbers which followed the original outbreak of myxomatosis, and the advancement of reed and sallow in Westwood Marsh, with great reduction of the open water space. These changes can only partly explain a continuing decrease in the breeding numbers of many heathland and water birds. Changes in the heath and woodland Two types of heathland can be recognised at Walberswick, the exposed heather or gorse/bramble dominated areas typical of the poorer stony soils, and the grass and bracken covered areas found on better soils near wood or marsh edges. Both types of habitat altered rapidly in character in the years immediately following myxomatosis introduction in 1954. Short-cropped areas became confined to a few wood edges, fine wiry grasses gave way to coarser more succulent species, bracken became more predominant, and gorse and bramble spread to form extensive patches, where a scattering of clumps and bushes had formerly existed. Compared with their former widespread abundance, rabbits are still scarce. The obvious changes due to myxomatosis are still in evidence in most heathland areas, although these have been reversed where rabbits have again established themselves in local concentrations. Rabbit reduction has presumably been one of the main factors responsible for the rapid spread of birch, over 100 acres of bracken heath have given way to birch woodland within the last fifteen years, and the process continues. Small oak trees too are now increasingly making an appearance, particularly in the damper
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areas bordering Westwood Marsh. Forestry Commission conifer plantations already covered many acres in 1950, and more trees were planted in the 1950s, which for several years supported species such as nightjars and tree pipits. These breeding areas have now, however, been lost. Changes in the marshland Most of the existing reedbeds of Westwood, Corporation, and Reedland Marshes were rapidly established in the immediate postwar years. About a quarter of this area was still open water in the early 1950s, but this has been considerably reduced. Reed encroachment on the mere edges was temporarily arrested by the presence of numerous coypus between 1958 and 1962, but has continued more rapidly since. At present, the few small remaining meres occupy somewhat less than ten per cent of the total reed marsh. Most of the reedbeds are covered by no more than a few inches of water for much of the year. In these conditions, many marsh edges have become increasingly dominated by sallow, and the area of fen bordering the inland end of Westwood Marsh has extended greatly since 1965. Changes have also occurred in the salt marsh behind the sea wall, but some of these are hard to define. This whole area has become far less attractive to waders, and to certain breeding species since 1960. Food changes resulting from the continuous seepage of salt water through the sea wall and into the Dunwich River may be largely responsible. Repeated winter breaks in the sea wall have recently increased the area dominated by shingle. Notes on the breeding of individual species in the Walberswick area, 1953-72 An account is given below of the breeding of locally distributed heath and marshland birds at Walberswick over the last twenty years, with comment on other species whose status has undergone marked change during the period. Few breeding counts, or even estimates, were made prior to 1959, and for most species only generalised remarks are possible about the Situation in the 1950s. In most seasons since 1960, however, breeding counts have been made for certain species ( T A B L E 1 ) within the area. With appropriate allowance for non-resident early season passage birds, these counts have been based largely on records of territorial or singing males, or of displaying or calling pairs. Figures given represent pairs attempting to breed, rather than those successful. They should be taken as minimum figures for the area, but counting techniques and efficiency, however inaccurate, were comparable from one year to another. Little grebe. Formerly nested at Westwood. area up to 1965; none recorded breeding since.
At least one pair in the
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Bittern. About five booming sites in most years u p to 1962. in 1963, increasing to three to four in recent years.
Only two
Mallard. H a s decreased. Only a few broods (less than ten) now annually in evidence in Westwood Marsh. Teal. Nested in some numbers in the Fen Covert and Frederick's Wood areas u p to the early 1960s. N o w seldom seen at F e n ; only two to three females with young seen in Westwood Marsh in 1972 although still breeding at Frederick's Wood. Garganey. Present throughout s u m m e t (one to two pairs) and u n doubtedly nested in most years u p to 1959. Absent in the breeding season since then with the exception of 1968. Gadwall. About twenty pairs thought to breed each year around Westwood and Reedland Marshes up to the early 1960s. H a s greatly decreased; only two broods recorded at Westwood in 1972, and no more than six birds seen together during the breeding season. Shoveler. A few pairs bred, mostly around Westwood Marsh, into the early 1960s. It is doubtful whether any now nest at all. Shelduck. Continues to breed abundantly in old pine woods with bracken undergrowth between Westwood Marsh and the Blyth. Probably over 25 pairs in most recent years. Sparrow Hawk. F o u r to five pairs a year were known to keepers in the 1950s. By the early 1960s it had greatly decreased, and there has been evidence of no more than one to two pairs each year since (breeding not always proved). Marsh harrier. One to two nests successful each year, 1953-60. A pair returned 1965, two nests 1966-67, a single pair was unsuccessful 1968 but since then breeding has not been attempted. Kestrel. Decreased to only two known pairs in 1963-64. increased to the n u m b e r s of the late 1950s.
Thereafter
Coot. Has greatly decreased. Very few broods seen in 1972. Oyster catcher. Only one to two pairs now nest on the shore where there were regularly four to five pairs in the late 1950s. N o obvious change in the Blyth, where several pairs annually nest. Ringed plover. About twenty nested along the sea wall, WalberswickDunwich, in 1972; n o obvious decrease. Stone curlew. Very scarce since 1961. Several pairs bred at Hinton, Westleton, Dunwich, and Blythburgh in the 1950s, b u t only two to three pairs were located in the whole area in 1965, since when these low n u m b e r s have been maintained on agricultural land at H i n t o n and Blythburgh. Has ceased to breed on the heathland at Westleton and Dunwich. Common tern. A colony on D u n w i c h Shore Pools, 1956-62, n u m b e r e d u p to forty nests. Only an odd pair or two has nested there during the last ten years. Little tern. A b u n d a n t from Walberswick village to Dunwich in the early 1950s. T w e n t y pairs were estimated in 1957; this had decreased to only three known pairs in 1969 and one pair in 1971. An increase to six pairs in 1972 resulted from the formation of a new shingle fan by winter sea flooding. Collared dove. First recorded in the area in 1961. 1963, abundantly since 1964.
Has bred since
Cuckoo. Annual fluctuations, but no evidence of m u c h change in n u m b e r s in this area. Barn owl. Decreased between 1959 and 1965. N o w probably about three pairs most years.
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Little owl. Decreased even more markedly than the barn owl, 1957-65; formerly common. Long-eared owl. Breeding or attempted breeding proved in most recent years; one to three pairs regularly since 1959. Short-eared owl. One pair successful and another may have bred 1959; probably also bred in 1958. Nightjar. Numbers remained fairly constant in the early 1960s, but have fallen somewhat since 1965 (TABLE 1). Has disappeared from several localities where an odd pair or two were resident ten years ago. Wryneck. One pair successful from 1953 until 1957. No records since. Woodlark. Common on forestry edges and in rabbit warren areas up to 1954, then declined rapidly in the years following the outbreak of myxomatosis. Still over ten pairs around Blythburgh Fen alone in 1956, but by 1959 no more than four pairs could be located in the whole area. The last probable nesting was in 1963. Willow tit. Scarce; regularly breeds in at least two damp woodland areas. Bearded tit. From less than ten pairs in 1953, after the East Coast floods, numbers rose to an estimated thirty pairs in 1958 and over fifty pairs in 1959-62; following approximatelyfiftyper Cent reduction after the winter 1962/63, continued to increase to probably a hundred pairs or more in 1972. Wheatear. Bred until 1955 on most patches of heathland. Declined rapidly immediately after the decline in rabbit numbers, with none recorded nesting after 1958. Stonechat. First bred on Westleton Heath in 1956. Has now nested regularly at Westleton since 1959, with an occasional pair or two at Blythburgh and Walberswick. Whinchat. Still common on most heaths in 1959, when there were seven pairs nesting on Westleton Heath alone andfivepairs at Blythburgh Fen. Decreased rapidly in the early 1960s (TABLE 1). Since 1965 only an odd breeding pair or two have been found each year, usually at Westleton. Redstart. A gradual decrease. Now less than half as many as bred in the mid-1950s when breeding occurred in many woods at Dunwich from which the species has been absent since 1960. Last nested in Sandymount Covert, 1959. In the last stronghold, the pine/birch woodland between Fen Covert and the Blyth, it has declined over the last two or three years (TABLE 1). Nightingale. A slight decrease. Absent from several thickets which always used to hold a pair. Still a common species in the area. 1972 breeding records low. Grasshopper warbler. A few pairs only around the back of Westwood Marsh up to the early 1960s. A dramatic increase occurred between 1965 and 1969 (TABLE 1), and this species is now much more abundant and widespread, breeding on dry heaths and on the edges of salt marsh. Savi's Warbler. To judge from reeling behaviour, breeding almost certainly took place in 1969 (two other males holding territory); it was proved in 1970 (probably two pairs and two other territories held), and assumed in 1971 (two pairs) and 1972 (three pairs and one other territory held). Whitethroat. A gradual decrease in breeding numbers 1956-65; a drop of over seventy-five per cent in 1969, followed by a slight increase to less than 1968 levels.
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hesser whitethroat. N o apparent long term changes, b u t fluctuations from year to year. Of the Order of fifteen to twenty pairs in the area. Wood warbler. T w o pairs bred at Blythburgh Fen in 1959; a male held territory at the same place for several weeks, 1962. Yellow wagtail. Perhaps a slight decrease in n u m b e r s nesting on the heathland (eight pairs counted in 1960, five in 1972). A great decrease in n u m b e r s nesting on the shore between Walberswick and Dunwich. Tree pipit. A slight decrease during the 1960s when birds left areas of young planted forest as the trees become too tall. Otherwise this species has maintained its n u m b e r s well (TABLE 1). Particularly a b u n d a n t at Blythburgh Fen, which now usually accounts for about half the known pairs. Red-backed shrike. Certainly no less than thirty pairs in the area in 1955-56. Decreased steadily to 1964, but n u m b e r s have been maintained since (TABLE 1). It remains to be seen whether the substantial drop in 1972 is permanent. T h i s species had virtually left Westleton H e a t h by 1960 and Blythburgh H e a t h by 1965, and has become extremely localised. Siskin. Occasional at Blythburgh Fen in s u m m e r in the early 1960s; breeding proved 1962. Redpoll. A n occasional pair probably bred most years in the 1950s, but this species was then very scarce in summer. Increased dramatically, becoming a b u n d a n t in 1963. Crossbill. Breeding proved only during 1963. Com bunting. H a d ceased to breed at Hinton by 1955 or earlier, b u t was still n u m e r o u s at Westleton (at least ten pairs in our area north of the D u n w i c h Road). Declined here to five located singing birds in 1964, t w o in 1969, one in 1970, and none since.
Discussion As far as specialised heathland birds are concerned, the picture at Walberswick over the past two decades has been one of general breeding decline. Wryneck, wheatear, woodlark, and com bunting have disappeared completely, whilst nightjar, stone curlew, whinchat, redstart, whitethroat, and red-backed shrike have greatly decreased. Stonechat and redpoll represent breeding gains; otherwise only the tree pipit has maintained its numbers of the 1950s. The rapid disappearance of the wheatear and the woodlark was undoubtedly precipitated by lack of rabbits after 1954. Large falls in numbers of red-backed shrikes and stone curlews between 1956 and 1961, of whinchats between 1959 and 1964, and of nightjars and redstarts in recent years are less easy to correlate with obvious vegetational changes. These decreases have all involved complete disappearances from sites with apparently quite suitable habitat, and the species concerned have become much more locally distributed. Recent nightjar losses are partly explained by conifers having grown too tall in a Forestry Commission area at Westleton which supported several pairs when newly planted. It is possible that subtle ecological adjustments to rabbit reduction, continuing during the 1960s, have adversely affected breeding bird numbers. More likely, decreases
157 observed at Walberswick reflect the general decline in heathland species in south-east England which has resulted from widespread habitat destruction, coupled possibly with long-term climatic change. With the progressive reduction in the area of open water, there has been a marked decrease during the last ten years in numbers of breeding duck and coot in and around Westwood and Reedland Marshes. Teal and gadwall, once quite numerous, have become very scarce, and garganey are no longer seen except on passage. Duck populations may have been affected by reduced availability of nesting sites resulting from changes in the cattle grazing methods employed on the borders of the marsh. The failure of the marsh harrier to maintain itself as a breeding species has presumably in turn been a consequence of the low numbers of young ducks and coots now present in the marsh during the late breeding season. As a non-breeding bird the marsh harrier is still seen as regularly as in the past. Certain specialised reedbed nesters have continued toflourishat Walberswick, notably the bittern, the grasshopper warbler, and the bearded tit. In parallel with the dramatic recent increase in grasshopper warbler numbers has been the establishment of a small colony of Savi's warblers in Westwood Marsh, which shows signs of slowly increasing. The raised breeding fortunes of these two Locustella species are probably not the result of the spread of sallow. Although now more extensive than in the past, considerable areas of scattered sallow have existed at the back of Westwood Marsh for many years. Both species, although normally recorded near sallow clumps, have been found holding territory, and presumably breeding, in areas of pure reed over 300 yards from the nearest small bush. Although encouraging, these marshland breeding gains must be kept in perspective. They hardly offset the loss of the marsh harrier or the breeding duck variety for which the Walberswick area was notablefifteenyears ago. BREEDING BIRDS IN THE WALBERSWICK AREA
TABLE 1
Numbers of breeding pairs of certain species in the Walberswick area, 1960-72. i960 1961 1962 1963 1964 1965 1969 1970 1 Long-eared owl 2-3 1 1 2-3 2 1 2 1 2 6 4 3-4 4-6 3-4 2-3 2 2 2-3 Stone curlew Nightjar 16 14 16 18 15 16 14 10 7 Woodlark 2 2 2 1 Whinchat 12 11 8 5 4 2 2 2 2 2 4 5 3 3 2 5 5 3 Stonechat Redstart 18 14 20 18 16 18 15 12 9 Grasshopper warbler 6 7 8 8 8 10 25 + 25 + 25 + •—• Savi's warbler 1 2-3 3-4 Tree pipit 27 24 25 26 22 23 22 19 24 Red-backed shrike 13 11 15 12 8 8 14 13 6-7 —
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D. jf. Pearson, cjo Brouses, Sibton, Saxmundham, Suffolk