S Eltringham, G Atkinson-Willes
A method is described of obtaining indices to represent the relative abundance of ducks in the same m onth of different years and in each season as a whole. Results are based on the sample which has been used since September 1959 to produce m onthly reports for observers in the N ational Wildfowl Count Scheme. The species investigated are Tufted Duck, Pochard, M allard, Teal and Wigeon, and the m onths under consideration September to M arch inclusive. The period covered is from autum n 1948 to
more » ... spring 1960. The Tufted Duck in G reat Britain has shown an average annual increase of about &i% and has doubled its winter population within the period under review. This rate of increase agrees well with two other estim ates; one based on an unpublished study of the survival of ringed adults and of breeding success in England during the period 1949-1957. the other on the results of a survey m ade in the London area between 1950 and 1957. The m onthly indices also agree w ith those obtained by a different method from a m uch larger sample of Wildfowl Counts. The increase in Pochard wintering in this country is equivalent to an annual rise of nearly 5% over the full twelve years. The whole of this, however, took place in the three years 1951-1954, and there has been no significant change since. O f the other species, M allard increased steadily at an annual rate of about 2ì% ; Wigeon showed no significant tren d ; and neither did Teal, although in 1959-60 an unusually large influx occurred. By comparison with previous analyses it seems that the num ber of M allard in October 1959 was exceptional, and that the bulk of the Teal entered and left this country about a m onth earlier than usual.