| Summary: | An increase in fox numbers in Aberdeenshire,dating from the early 1950's, was documented from parish bounty returns. Extending its range, the fox reached the coastal National Nature Reserve, "the Sands of Forvie", in about 1962 and subsequent depredations of nesting birds there initiated this study. Numbers were considered still to be increasing, though data on fox range sizes suggested that this will cease within a decade. Fox scats from Forvie showed the diet consisted mainly of rabbits in all seasons with wildfowl second in importance. In surrounding areas stomach analysis showed similar results though game-birds replaced the wildfowl. Rabbits were counted on Forvie on dawn transects and there was little annual change in numbers. Consistent seasonal changes were not reflected in any difference in fox diet. Rabbits may act as a 'buffer' protecting birds from more serious predation. Nesting female eider duck were the birds most frequently subject to predation, though overall their breeding success was similar to that found before foxes arrived. In one rushy area fox predation was significant, possibly related to denser nesting there. It was estimated that adult foxes and cubs consumed up to 4% of the adult female eiders in any year,which represents almost half of their annual mortality previously. The Forvie eider population, which does recruit from elsewhere, has not decreased or shown a detectable change in sex ratio since foxes arrived. In the past the nesting of terns on Forvie was seriously disrupted by foxes but the continued use of an electric fence has contributed to successful seasons since 1974. Suggestions for improving its efficiency were given, together with methods for monitoring the levels of fox predation, which will indicate if fox numbers should be reduced. The impact of foxes on prey species in other studies was considered and it was concluded/that the Forvie eider population could withstand present predation levels.
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