Field experience during the 1984-88 survey suggested an average density of five pairs per tetrad, from which a county total of 1,000 nests was calculated. The figure derived from the 1988-91 National Atlas was marginally lower. The BBS assessed there was a 21% decrease in Wales between 1994 and 2007, which if applicable to Pembrokeshire suggests a breeding population of a little less than 800 pairs at the end of the 2003-07 survey. Winter survival of Treecreepers decreases with an increase in wet weather. The trend towards wetter winters in Wales during the past fifteen years may well be at least part of the explanation for the reduced breeding population.
Graham Rees
Fieldwork 2003-07 (based on 490 tetrads)
Red = breeding confirmed = 64
Orange = breeding probable = 95
Yellow = breeding possible = 38
Total tetrads in which registered = 197 (40.2%)