Breeding summer visitor and passage migrant. Not recorded from December to February
|No of tetrads occupied||427 (of 478)|
|Percentage of tetrads||89.3%|
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.