Wren - 2003-07

The estimate of 40,000 breeding pairs accompanying the 1984-88 survey was based on an estimated average density of 100 pairs per tetrad. The UK national average was assessed as being 120 pairs per tetrad. The lower estimated density in Pembrokeshire was based on the premise that the predominant pastureland would hold fewer birds than richer habitat to be found further east. However, subsequent findings have shown that density is high in areas of pasture, and the 1988-91 National Atlas, depicts maximum abundance in Pembrokeshire as a whole. It seems reasonably safe therefore to apply the UK value to the 2003-07 results, taking into account that the BBS indicates a 12% increase in Wales between 1994 and 2007. This results in an estimate of about 62,000 pairs breeding in the county. The population is expressed in pairs but Wrens are often polygamous, especially in prime habitat such as deciduous woodland.

Wrens can suffer high mortality during cold winters but there were unbroken mild winters during the years between the two local surveys, which would have been a major factor in the steady increase in their population.

Graham Rees

 

Fieldwork 2003-07 (based on 490 tetrads)

Red = breeding confirmed = 195

Orange = breeding probable = 265

Yellow = breeding possible = 7

Total tetrads in which registered = 467 (95.3%)