A re-survey of the distribution of the bridled form of the common guillemot, Uria aalge, during 1948-50 has shown that in the ten years since the first survey was made, four colonies have decreased significantly in percentage of bridled birds and one has increased. The total number of colonies for which satisfactory comparisons were obtained was only eighteen. Discrepancies between observers made it necessary to accept only those counts which had been checked by other observers. This result is not statistically significant, but various facts suggest that a decrease in bridled birds is in progress and it is certainly worth continuing the investigation at ten year intervals.
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