Changes in the population size and nest sites of Merlins Falco columbarius in Wales between 1970 and 1991

Annual surveys of breeding Merlins were carried out between 1970 and 1991 with more systematic effort from 1982 onwards. Mean annual occupancy rates did not differ significantly between heather, moorland tree and conifer plantation nest areas. Mean occupancy rates declined significantly in heather and moorland tree nest areas between 1970 and 1991. These declines are probably associated with a progressive switch to conifer plantation nest areas that have ultimately affected over 50% of breeding pairs. The Welsh population has probably remained relatively stable throughout the study period at approximately 60-70 pairs. The switch to conifer plantations is related to habitat; the switch was most pronounced on the grass moors of central and south Wales and probably occurred between 1975 and 1985, whereas on the heather moors of north Wales only a small number of ground-nesting sites have been vacated since 1985. This was partly due to the lack of afforestation on most of the Berwyn Mountains. The population changes in Wales are compared with those in other regions of Britain. It is suggested that, with the exception of the Northern Isles, the British breeding Merlin population no longer merits special conservation concern and should be removed from the 'Red Data' list of British birds. However, its sensitivity to toxic contamination makes it a most useful environmental indicator species and future monitoring of populations is highly desirable.