Northern Willow Warbler - 1949 status

Phylloscopus trochilus acredula

Recorded at Skokholm 25 and 27 May 1936, and 2 and 12 May 1937.

R.M.Lockley, G.C.S.Ingram, H.M.Salmon, 1949, The Birds of Pembrokeshire, The West Wales Field Society

Willow Warbler - 1949 status

Phylloscopus trochilus trochilus

Common summer visitor, and abundant passage migrant, arrives last week in March.

He also mentions, under the section of the book on Land-Birds:

The first Willow-Warblers are trapped at Skokholm during the last week of March.  This is one of the largest small bird migrations in Pembrokeshire, and for the whole month between mid-April and mid-May there are days when the county swarms with these charming singers.

R.M.Lockley, G.C.S.Ingram, H.M.Salmon, 1949, The Birds of Pembrokeshire, The West Wales Field Society

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%)

Willow Warbler - 1994

Breeding summer visitor and passage migrant. Not recorded from December to February

The Willow Warbler was a common summer visitor according to both Mathew (1894) and Lockley et al. (1949), the latter adding that it was also an abundant passage migrant.

It is a widespread breeding species in Pembrokeshire today (see map) being particularly numerous in some scrub areas, including Castlebythe Common and Waun Cleddau. Using census figures from Dyfed Wildlife Trust reserves as a guide, the average density of Willow Warblers is estimated to be about 100 pairs per tetrad and the total population about 43,000 pairs.

The first Willow Warblers usually arrive during the last few days of March or the beginning of April, though occasionally from 15 March and one was at Skomer on 6 March 1966. Large numbers pass through, with many falls of 100 or more at headlands and islands, including 250 at Skomer on 23 April 1987 and an exceptional 1,000 there on 18 April 1985. Passage continues until mid-, sometimes late, June.

Autumn passage extends from mid-July to early October with stragglers to 24 October. One bird was singing at Goodwick on 28 November 1959. Autumn falls are generally smaller than those in spring, with 40 to 50 birds typically occurring at any locality. Larger counts, up to 150, have been noted, and an exceptional 3,000 birds were at Skokholm in August 1948.

Grey-brown and silvery coloured Willow Warblers have been noted at Skokholm in April and May, and the north European and Siberian subspecies acredula was identified in the hand on 7 and 12 May 1960.

One was seen and heard singing at Stackpole on 9 February 1991.

Fieldwork 1984-88 (based on 478 tetrads) 

Red = breeding confirmed = 166

Orange = breeding probable = 253

Yellow = breeding possible = 8

Total tetrads in which registered = 427 (89.3%)

Donovan J.W. & Rees G.H (1994), Birds of Pembrokeshire

Willow Warbler - 1970s breeding

Red = breeding confirmed

Orange = breeding probable

Yellow = breeding possible

Willow Warbler - 1894

Phylloscopus trochilus

A not very numerous summer visitor. A nest found at Stone Hall, near a pond much frequented by Herons, was entirely lined with the small grey feathers of those birds.

Mathew M.A. 1894, Birds of Pembrokeshire and it's Islands