Willow Warbler - 2003-07

This leaf warbler is familiar to many by virtue of its liquid, cascading song. A summer visitor to Britain, wintering in southern Africa, it is normally present in Pembrokeshire from April to September. Scrub, woodland edge and recently planted woodland are its prime habitat, where nests are placed on the ground concealed by vegetation. Willow warblers are normally absent as a breeding bird from the offshore islands, except for the partially wooded Caldey and are not usually found breeding in gardens.

The population estimate which accompanied the 1984-88 survey is now considered to be unsound. Census results from Dyfed Wildlife Trust reserves were applied across the whole county without taking habitat into account, and resulted in an inflated value. Had the findings of the 1988-91 National Atlas been available, a national average value could have been applied and would have resulted in a more realistic estimate of 13,500 pairs nesting in the county.

Comparing the results of the two local surveys indicate a retraction in distribution. The BBS suggests a 20% decrease in Wales between 1994 and 2007, which if applied to Pembrokeshire results in a population estimate of approaching 10,000 pairs nesting by 2007. This accords with the subjective opinion, that Willow Warblers were less numerous during 2003-07 survey than they were during the 1984-88 survey.

Evidence is emerging that this marked decrease is probably due to unfavourable conditions prevailing in the Willow Warblers’ tropical African wintering area.

Graham Rees

 

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed = 47

Orange = breeding probable = 307

Yellow = breeding possible = 15

Total tetrads in which registered = 369 (75.3%)

Chiffchaff - 2003-07

The repetitive song which gives the Chiffchaff its name is a familiar sound in the summer time. It favours deciduous rather than coniferous trees but is widespread in the county. The domed nest is usually well concealed and placed low down in the available vegetation.

Chiffchaff numbers have been increasing across Europe since about 1980. The first estimate of the Pembrokeshire breeding population was made following the results of the 1984-88 survey. At an average density of 15 pairs per occupied tetrad, a total of 6,000 pairs was suggested.

By the end of the 2003-07 survey a 13% spread in distribution had been plotted in Pembrokeshire and the BBS noted a 42% increase in Wales between 1994 and 2007. Using these figures an estimate of 8,500 pairs breeding in the county by 2007 emerged.

Graham Rees

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed = 101

Orange = breeding probable = 319

Yellow = breeding possible = 8

Total tetrads in which registered = 428 (87.3%)

Wood Warbler - 2003-07

This summer visitor is the largest and most colourful of the British leaf warblers, its green upperparts contrasting with its bright yellow breast and silky white belly. Seeing the male trembling while it delivers its trilling song is a fulfilling experience. Closed canopy woodland with little understory is the favoured habitat, where the nest is concealed on the ground among rank vegetation.

About a third of the UK population is found in Wales, where ideal habitat of deciduous woodland grazed by sheep has very little understory growth. Those breeding in Pembrokeshire are at the periphery of their distribution and have been found to be less abundant than in the main area. This may in part reflect the fact that the majority of county’s woodlands are not grazed and the understory and shrub layers are too dense for this species.

The UK population was estimated at 17,200 singing males in 1984–85 and the Pembrokeshire total at 250 singing males in 1988. A subsequent steady decline has been detected across northern and western Europe, the UK total being estimated at 9,000 -10,500 by the year 2000. The 2003-07 Pembrokeshire survey found that distribution had decreased by 50% compared with 1984-88, the remaining total being no more than 100 singing males, perhaps fewer.

Graham Rees

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed = 3

Orange = breeding probable = 19

Yellow = breeding possible = 3

Total tetrads in which registered = 25 (5.1%)

Dartford Warbler - 2003-07

The dark, long-tailed, vinous-breasted, resident Dartford Warbler is a rare breeding bird in Britain, with a population of less than 2,000 pairs. It inhabits heathland with gorse and heather. Although skulking within such habitat it does occasionally sing from the tops of gorse sprays. The nest is concealed within deep cover.

Historically Dartford Warblers have been confined to southern England, mostly found in Hampshire and Dorset, where numbers were reduced during severe cold winters but recovered in milder following years. The successive “Arctic” winters of 1961–62 and 1962–63 drastically reduced the population, with only 11 pairs known to have survived. The mild winters which have since prevailed enabled them not only to steadily increase but also to expand their range, principally to the west.

In Wales they were breeding in Gwent by 1998, in Glamorgan by 2000 and in the first year of the Pembrokeshire Breeding Birds Survey of 2003-07 up to six pairs were confirmed to be breeding at one locality. By the end of 2007 they had been found in eight tetrads, with a total population of 13 – 15 pairs. All were in lowland areas, none having yet been found in uplands as has been the case in Somerset, Devon and the Brecon Beacons.

Graham Rees

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed

Orange = breeding probable

Whitethroat - 2003-07

Whitethroats are perky, largely brown warblers are widespread in the county during the summer. They are particularly evident during their frequently performed song flights, when their disjointed, scratchy song draws attention to their presence. They inhabit heathlands, scrub, hedgerows, woodland edge and very young tree plantations. Nests are placed in low bushes, nettles, brambles and tall grass.

The map shows a similar distribution between the two local surveys at the tetrad level. Some minor changes were noted at a more local level, where young plantations had grown to the point where they became untenable for Whitethroats. Assessing population levels at any given time has been complicated by periodic collapses in numbers. In 1969 the British population was reduced by about 77%. This was associated with drought conditions in the African area where Whitethroats winter. Subsequent recovery has been interrupted by further population crashes of varying magnitude. By 1974 the breeding population had stabilized at approaching half the pre 1969 level but the subsequent recovery was interrupted by another crash in 1984. The 1984-88 Pembrokeshire survey took place in a period of recovery and by 1988 it was estimated to have reached an average density of 20 pairs per tetrad, giving a county total of 8,000 pairs. The similar returns for the 2003-07 survey would seem to indicate no change in the county population but in the meantime the BBS calculated a 10% increase between 1994 and 2007 but a decrease of 18% between 2000 and 2005. It seems that the estimate of 8,000 pairs in Pembrokeshire by 2007 is realistic, despite fluctuations during the time between the two local surveys.

Graham Rees

 

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed = 115

Orange = breeding probable = 289

Yellow = breeding possible = 12

Total tetrads in which registered = 416 (84.9%)

Lesser Whitethroat - 2003-07

The Lesser Whitethroat, a summer visitor, is an inconspicuous warbler which favours deep cover. Its most notable feature when seen well is its black patch through the eye. Its monotone rattling song often reveals its presence in the scrubby areas it frequents and where it nests.

No way has been found to separate possible passage birds from the records when evaluating the results of the 1984-88 survey. A minimal density of one pair per tetrad was used to estimate a county breeding population of 70 pairs. The 1988-91 National Atlas shows an abundance distribution where the Pembrokeshire density was much lower than the UK average of just over two per tetrad, suggesting that the local estimate was realistic. The same situation existed when assessing the returns from the 2003-07 survey, so the county estimate remains the same. Nonetheless the uncertainty of the impact of migrants being involved, means it should be regarded as a maximum and the true level might have been smaller, for the BTO considered that the UK population dropped to about 64,000 pairs by the year 2000 from an estimated 80,000 in 1991.

Graham Rees

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed = 4

Orange = breeding probable = 66

Yellow = breeding possible = 9

Total tetrads in which registered = 79 (16.1%)

Garden Warbler 2003-07

Surely it was this summer visitor that inspired the acronym LBJ (little brown job). It does however possess a pleasant mellow warbling song, though its critics often refer to this as being like a “garbled Blackcap”. It nests low down in shrubs and trees around woodland edge, rides and glades.

The 2003-07 survey found a marked absence in the extreme south compared to the 1984-88 presence. Nonetheless the totals registered for each of the two surveys was identical. The abundance map in the 1988-91 National Atlas indicates near maximum density in Pembrokeshire, which suggests the 1988 county estimate of 2,000 pairs was realistic. Since then the BTO has used a number of survey methods to conclude that although there have been short term fluctuations in the population, there has been a shallow long term decline. The BBS quantifies this as a 25% decrease in Wales between 1994 and 2007, which suggests the Pembrokeshire population had dropped to about 1,500 pairs by 2007.

Graham Rees

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed = 14

Orange = breeding probable = 163

Yellow = breeding possible = 16

Total tetrads in which registered = 193 (39.4%)

Blackcap - 2003-07

A predominantly grey warbler, the male with a distinctive black cap, the female’s cap ginger, the Blackcap inhabits the cover of trees and scrub, where it nests. It is found in all bar the barest parts of the county. Its melodic, fluty, song draws attention to its presence but it can be difficult to locate. Most Blackcaps are summer visitors to Pembrokeshire.

A variety of monitoring schemes have concluded that Blackcaps have been consistently increasing since at least the 1970’s. Despite much conjecture, no convincing explanation has been suggested as to why this has been so. The 2003-07 county survey found that there had been a 17% increase in distribution compared with that found in 1984-88.  The BBS has calculated an increase of 87% in Wales between 1994 and 2007. Applying these increases locally suggests approaching 13,000 pairs were breeding in Pembrokeshire at the end of 2007, compared to 7,000 pairs estimated in 1988. 

Graham Rees

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed = 71

Orange = breeding probable = 317

Yellow = breeding possible = 9

Total tetrads in which registered = 397 (81%)

Reed Warbler - 2003-07

This summer visitor’s appearance is plain, with unstreaked brown upperparts and buff underparts.  Its slow chattering song is usually the first indication of its presence in the deep cover of reedbeds, its principal habitat. Its nest is intricately woven around the stems of reeds.

The Reed Warbler has slowly expanded its range in Britain from about the 1960’s, in Pembrokeshire from1974, with breeding proven in 1975. By the time of the 1984-88 survey an estimated 60 pairs were breeding in the county. The estimate was made after some time spent in the main localities and was based largely on singing birds. Assessing the Canaston reedbed (also referred to as Minwear or Slebech reedbed) was made particularly easy because the local shooting syndicate had cut rides through the reeds the previous winter. (Note that although the largest concentration in the district has been the Teifi Marshes, the majority of them have been in Ceredigion, so only a small fraction qualified for inclusion in Pembrokeshire assessments).

By the close of the 2003-07 survey an increase of 48% in distribution had been plotted but it is unlikely that this represents an increase in population of this magnitude. New sites were in small areas of reeds around ponds and along river banks, which did not have the carrying capacity of major reedbeds. On the premise that about 10 pairs were added in these new sites and that the main population remained stable, as it has nationally, there were probably about 70 pairs nesting in Pembrokeshire by 2007. Although the population estimates have been given in pairs, they are mainly based on singing birds and some of these may not have attracted mates, which is not uncommon among Reed Warblers.

Graham Rees

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed = 7

Orange = breeding probable = 24

Total tetrads in which registered = 31 (6.3%)

Sedge Warbler - 2003-07

The Sedge Warbler is a small, chubby warbler with brown upperparts streaked black, creamy white underparts and a broad cream stripe above the eye. Its varied chattering song is often delivered whilst it is perched in full view or in its song–flight. It is to be found mostly in damp places like reedbeds, bogs and around ponds. Its nest is placed in bushes or tall vegetation, near or on the ground. It is a summer visitor.

The UK population level has varied considerably over the years, affected mainly by varying rainfall in its winter quarters in West Africa. Analysis of various data sets gathered by the BTO shows year to year fluctuations, with similar levels of population in the UK in the years 1988 and 2007, which is relevant to the two local surveys. The 2003-07 survey results show an almost 10% increase compared with those of 1984-88.This suggests that about 700 pairs were nesting in Pembrokeshire at the end of 2007, compared to 650 pairs in 1988.

Graham Rees

 

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed = 27

Orange = breeding probable = 109

Yellow = breeding possible = 11

Total tetrads in which registered = 147 (30%)

Grasshopper Warbler - 2003-07

Interpretation of the comparative results of the two surveys is difficult. Young conifer plantations occupied during the earlier survey had matured to a state of unsuitability by the latter one. The BBS found an increase, on a UK national basis, of 68% since 1994 and by 24% between 2006 and 2007. This may have been in response to favourable conditions at their African wintering grounds resulting in increased survival.

The 1988-91 National Atlas indicated maximum abundance in Pembrokeshire, so it seems safe to apply the UK wide BBS figure to the county plot. This being so, there were probably 480 – 670 pairs breeding in Pembrokeshire at the end of 2007, compared with an estimated 400 pairs in 1988.

Graham Rees

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed = 2

Orange = breeding probable = 83

Yellow = breeding possible = 11

Total tetrads in which registered = 96 (19.6%)

Cetti's Warbler - 2003-07

Most records of Cetti's warblers are of singing males being heard. Since its colonisation, which began at Rhoscrowther in 1983, following the first one recorded at Bosherston in the winter of 1968, breeding has been variously established by trapping females with brood patches, seeing adults carrying food for nestlings, fledglings fresh out of the nest being observed and juveniles trapped at the close of the nesting season. Males are polygamous, serving up to four females, so singing males represent territories rather than pairs.

During the 1984-88 survey they were recorded at Rhoscrowther, Kilpaison, Pwllcrochan, Penally, Tenby and the Teifi Marshes, in a total of seven tetrads. Between surveys they were also found in the breeding season at Freshwater East, Castle Martin Corse and Llangloffan Fen. Numbers grew progressively at the Teifi Marshes to reach 23 singing males by 1995, all bar three of these being in Ceredigion, a short cold snap in the winter of 1996 almost eradicating them. By the time of the 2003-07 survey there were two singing males in the Pembrokeshire part of the Teifi Marshes, others being recorded at Tenby, Penally, the Ritec and at Goodwick Moor where fledglings were seen in 2006, covering a total of five tetrads.

Graham Rees

 

Fieldwork 2003-07 (based on 490 tetrads) 

Red = breeding confirmed = 1

Orange = breeding probable = 4

Total tetrads in which registered = 5 (1%)