Llanelli Naturalists Newsletter - Summer 1993 - No 55
DA Harris

Introduction.

During the late 1970's the RSPB conducted survey work on the breeding bird populations of virtually all the main upland blocks in Wales, aimed at assessing the relative ornithological importance of the different areas. Mynydd Du (also known as the Carmarthen Fans) was surveyed in 1978 by an RSPB fieldworker funded by the Brecon Beacons National Park. Most (but not all) of the area surveyed lies within the vice-county of Carmarthenshire.

The survey revealed that Mynydd Du was regionally important for breeding Wheatear Oenanthe oenanthe and Ring Ouzel Turdus torquatus; Wheatear densities of up to 13 pairs per 1 km were the highest recorded in any of the Welsh uplands. The Wheatear is a candidate Red Data Book species (Batten et al., 1990) with a northern and western bias to its distribution in Britain.

The primary aim of the 1992 survey was to census the breeding population of Wheatears on Mynydd Du and compare the results with those of the 1978 survey. Additionally, all other key species (see Table 1) were recorded, and their numbers and distribution compared with the previous survey.

Site description

Mynydd Du is dominated by the line of the north facing escarpment of the Old Red Sandstone which runs along its northern edge and westwards across the Brecon Beacons National Park where it forms the scarp-line of Fan Hir, Bannau Brycheiniog and Bannau Sir Gaer. The Old Red Sandstone scarp of Mynydd Du is dominated by scree and grazed bilberry. Further south, the land slopes gently down the dip slope of the sandstone and then over extensive exposures of Carboniferous Limestone and Millstone Grit. Rock outcrops are common over the whole area and the shallow soils support large tracts of mat grass and fescue grasslands. The only remaining area of heather moor is situated in the extreme west at Drysgol, and areas of ffridd (expanses of bracken and scattered trees and scrub above the main tree line) are largely restricted to the southern river valleys. The area is intensively grazed by sheep and the few small remaining blocks of peat suffer extensive erosion.

Key species.

When dealing with such large tracts of upland, it is not feasible to attempt to survey every species.    Attention was therefore concentrated on the following key species:

Red Kite    Lapwing    Dipper

Buzzard    Dunlin    Redstart

Goshawk    Snipe    Whinchat

Merlin    Curlew    Stonechat

Peregrine    Black-headed Gull    Wheatear

Red Grouse    Barn. Owl    Ring Ouzel

Black Grouse    Short-eared Owl    Grasshopper Warbler

Dotterel    Nightjar    Raven

Common Sandpiper    Tree Pipit    Linnet

Golden Plover    Grey Wagtail    Reed Bunting

Methodology

The bird survey method used is identical to- the one used in 1978 so that direct comparisons can be made. It represents a compromise between a mapping method (Enemar, 1959) and that used for the BTO "Atlas of Breeding Birds" (Sharrock, 1976). Every 1 km square was surveyed at least once. However, after the first visits individual areas were found to be so species-poor (containing only one Meadow Pipit and Skylark) that they were not re-visited in order to allow concentration on the areas with more diverse bird communities. These areas were visited from 4-6 times to confirm the presence of breeding pairs.

Information was obtained only on birds breeding in the open moorland habitats, therefore the survey boundary was the "top wall line" (TWL) - ie. the upper limit of enclosed land.

Results

The following tables summarise the information collected on:

(i)    The key breeding species recorded in 1978-1992 - Table 2

(ii)    The status of other bird species recorded in 1992 - Table 3

The survey was undertaken between 27.4.92 and 5.7.92.

Table 2. Key species - summary table of number of pairs in each survey. SPECIES    1978    1992

Buzzard    2    1

Peregrine Falcon    -    2

Kestrel    1    1

Red Grouse    1     

Lapwing    5    2

Golden. Plover    2    1

Common Sandpiper    10    .    8

Curlew    3    3

Snipe     3    5

Tree Pipit    6    10

Grey Wagtail    10    10

Grasshopper Warbler    2

Stonechat    3    1

Whinchat    11    9

Wheatear    281    345

Redstart    4    11

Ring Ouzel    17    8

Dipper    12    15

Reed Bunting    9    4

Raven    11    10

Table 3. Abundance and status of other species recorded.

SPECIES    ABUNDANCE    STATUS

Mallard    R    B

Grey Heron    0    FV

Pheasant    0    FV(Fr)

Black-headed Gull    0    FV

Stock Dove    S    B

Wood Pigeon    S    B(Fr)

Cuckoo    S    B

Swift    R    FV

Skylark    A    B

Swallow    R    FV

Housemartin    R    FV

Meadow Pipit    A    B

Pied Wagtail    C    B

Willow Warbler    S    B(Fr)

Pied Flycatcher    S    B

Blackbird    S    B(Fr)

Song Thrush    S    B(Fr)

Mistle Thrush    R    FV

Great Tit    S    B

Wren    C    B

Chaffinch    C    B(Fr)

Linnet    R    FV

Goldfinch    S    B(Fr)

Bullfinch    S    B(Fr)

Starling    R    FV

Magpie    S    B(Fr)

Jackdaw    R    FV

Rook    R    FV

Carrion Crow    C    8

Key to abbreviations used in Table 3

Abundance    Status

FV    Feeding Visitor only    R    Regular

LMV    Late Winter    or Passage    0    Occasional

    Visitor only    S    Scarce

B    Breeds (above    TWL)    C    Common

(Fr)    Mainly restricted to    A    Abundant

Ffridd areas

Discussion

The extensive areas of rock outcrops and boulder scree interspersed with patches of short grassy turf in the area are ideal Wheatear habitat. The densities of up to 13 pairs in a single 1 km square are the highest recorded in upland Wales, and the continuance of sheep grazing to maintain a short grass sward is important for this species. The total number of breeding pairs recorded in 1992 (345) was higher than in 1978 (281), but not all areas were surveyed for this species in 1978 (Davies, 1978). It is therefore difficult to assess whether there has been a genuine increase over this period, but comparison of the two surveys indicates that there may have been an increase in both numbers and distribution.

The numbers of breeding Tree Pipit and Redstart also show an increase since 1978, but again some of the ffridd areas in which they were located were not surveyed during the previous survey. The number of breeding Stonechat and Whinchat however have declined, although elsewhere in Wales the latter species was very successful (Griffin & Rowland, 1992). Areas of ffridd in the Carmarthen Fans are restricted to a few sites, probably because the shallow soils do not allow for growth of bracken which requires a minimum soil depth of nine inches (Pearsall, 1968). However, the sample size for all these species is so small that it not possible to draw definite conclusions from the results.

The only breeding species which has apparently disappeared from the study area in the period between the two surveys is the Red Grouse, although there have been sightings reported on the remaining areas of heather on the south-western flanks of Mynydd Du. This bird has declined markedly from most Welsh moors over the past 50 years and no birds were found in the area during a national survey in 1990-91 (Williams at al., 1991). However, Roberts (1992) reports that one or two birds are seen here on occasion, although he gives no specific records since 1983. Ring Ouzels have shown a marked decline on Mynydd Du from 17 pairs in 1978 to only 8 in 1992 (-53%). Although the population of this species is known to fluctuate quite considerably from year to year on Mynydd Du, it is likely that the results of the survey constitute a real decline.

The Red Grouse in particular has been affected by the high grazing levels on the moor which has resulted in the loss and degeneration of heather, and Ring Ouzels may have declined as a result of the loss of heather and bilberry, although increased recreation pressure has also been suggested as a reason for declines in the past (Tyler & Green, 1989). Additionally, Ring Ouzel populations are subject to natural fluctuations.

Two new breeding species were recorded in in 1992 - the Peregrine Falcon and the Grasshopper Warbler. In 1978, Peregrines were still recovering from the effects of pesticides in the 1950's and 60's, but a survey in 1991 revealed that not only had the population fully recovered, but numbers were much higher than the estimated pre-war total (Williams, in press). Grasshopper Warblers have also increased in many parts of Wales recently, and some of the wet, rushy flushes on Mynydd Du provide ideal habitat for this species.

The river corridors of the Fans support a diverse range of bird species. Many supported high densities of Dippers and Grey Wagtails where the upland streams flow over base-rich sandstones and therefore provide an abundance of insects and other riparian invertebrates. These valleys also support high densities of Wheatear, and ffridd-dependant species such as Whinchat are confined t.6 these more sheltered areas.

One of the most pressing conservation issues in Wales at present is the decline of breeding waders (Tyler, in press). Although the sample size is small, the results of this survey confirm that the number of Lapwing in particular has shown a marked decrease since the previous survey. The populations of Curlew and Snipe appear to be stable, but suitable breeding habitat for these two species within the study area is confined to the few wet flushes. The lack of wetter feeding areas has also affected breeding Golden Plover, with only one pair nesting in 1992. Again, this mirrors a much more widespread decline in this species in Wales (Leversley at al., 1990).

It is important to note the increase in the number of Red Kite sightings compared to the 1978 survey, with birds recorded foraging over the hills on most visits in 1992.

Mynydd Du should also be noted as an important area for passage waders in early spring, with large flocks of Golden Plover recorded along with small trips of Dotterel.

The results of the survey therefore reveal that this area continues to support important numbers of breeding Wheatear, but that since the last survey in 1978, its importance for breeding Ring Ouzel has probably diminished. The heavily grazed grass moors and rock outcrops provide ideal breeding and feeding habitat for Wheatears, but the high stocking densities have resulted in the loss of heather and bilberry, and thus a decrease in Red Grouse, and possibly Ring Ouzel, numbers.

References

Davies, M. 1978. Upland bird surveys in the Brecon Beacons National Park. Unpublished RSPB Report.

Fuller, R J. 1982. Bird Habitats in Britain. T & A D Poyser.

Griffin, B & Rowland, G. 1992. Breeding Hen Harriers in Wales. Unpublished RSPB Report.

Leversley, P, Williams, I, Griffin, B & Brooks, D. 1990. Breeding Dunlin and Golden Plover on the Elan uplands. Unpublished RSPB Report.

Merchant, J H, Hudson, R, Carter, S P and Whittington, P. 1990. Pooulation trends in British Breeding Birds. BTO Tring.

Nethersole-Thompson, D. 1986. Waders - their breeding haunts and watchers. T & A D Poyser.

Parr, S J & Williams, I. 1990. Monitoring priorities for bird species in  Wales 1990-2000. RSPB Wales Office.

Pearsall, W H. 1968. Mountains and Moorlands. Collins.

Sharrock, J T R. 1976. Atlas of Breeding Birds in Britain and Ireland. T & A D Poyser.

Tyler, S J & Green, M. 1989. A preliminary study of the status and breeding performance of Ring Ouzels in Wales. Unpublished RSPB Report.

Tyler, S J. (In Press). A review of the status of breeding waders in Wales. Williams, I, Griffin, B & Holloway, D. 1991. The Red Grouse population of

Wales based on winter counts 1990/91. Unpublished RSPB Report.

Williams, I. (In Press). The Breeding population of the Peregrine Falcon (Falco peregrinus) in Wales, 1991.