- 1 This paper summarizes the results obtained from the Bridled Guillemot Enquiry organized by the British Trust for Ornithology. It is hoped to carry on the enquiry during 1939.
- 2 The biological problems of most interest connected with the enquiry are (a) how isolation has occurred in a previously more homogeneous population to produce the cline in proportion of bridled birds now observable from south to north, and (b) upon what genetic basis such proportions are maintained.
- 3 The results are given showing increase from < 0.25 per cent, in the south of England to 26 per cent, in the Shetlands, with two lines of discontinuity in the cline; beyond the British Isles the increase is continued up to 70–80 per cent, in the Westmann Islands, Iceland.
- 4 The question of the races shows another cline existing in Guillemot populations. There is not complete evidence to show that this is significantly correlated with the cline in bridling.
- 5 Previous work adds little but contradictions to the data gathered in 1938.