The Nuthatch is a sedentary bird, so it is likely that all summer records are of breeding birds. The estimate at the end of the survey of 1984-88 was made on this premise, suggesting an average density of three to four pairs per tetrad and a county population of 600 – 800 pairs. The higher of these figures accords with the average density used by the 1988-91 National Atlas to calculate the UK population.
Since then the BBS has indicated a 76% increase in Wales between 1994 and 2007. If the BBS findings are applied to the number of occupied tetrads registered by the survey of 2003-07, using a density of four pairs per tetrad, a population estimate of 1,500 pairs in Pembrokeshire emerges.
Graham Rees
Fieldwork 2003-07 (based on 490 tetrads)
Red = breeding confirmed = 84
Orange = breeding probable = 109
Yellow = breeding possible = 21
Total tetrads in which registered = 214 (43.7%)