The Index of Heron Population, 1936

the past year it has been possible still further to improve and to broaden the base of the national index started in 1934 in order to measure fluctuations in the breeding stock of Herons (Ardea c. cinerea). The index and the method of compiling it from returns sent in by observers all over England and Wales have already been described in British Birds (Vol. XXVIII., pp. 332-341), while the 1935 in...