GREAT BLUE HERON (ARDEA-HERODIAS) POPULATIONS IN ONTARIO - DATA FROM AND INSIGHTS ON THE USE OF VOLUNTEERS

Two censuses of Great Blue Heron (Ardea herodias) colonies in Ontario were conducted for the periods 1976-81 and 1986-91 respectively Volunt eers determined the location, status and size of every colony within t wo census areas for both periods. Validation nest counts were conducte d in 1990-91 to determine the proportion of total active nests in a co lony reported by volunteers and staff. Correction factors were applied to all nest count data so all results from the different count types would be comparable. The total number of heron pairs within the census areas was determined. Information on 1,613 colonies across the provin ce was collected from 1976-91, of which 48% had become extinct by 1991 and 67% had become established since 1976. The mean size of active co lonies in the census areas for the two periods was not different. With in the census areas, a 98% increase in the number of active colonies a nd a 55% increase in the number of heron pairs was observed from 1976- 91. This increase in Great Blue Heron numbers in Ontario follows simil ar demographic trends observed across North America.