Proceedings of the fourth meeting of the International Bird Census Committee and second meeting of the European Ornithological Atlas Committee / editors, J. Pinowski and K. Williamson, held 1972, Warsaw, Poland
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A method for monitoring changes in winter bird populations was tested in central Maryland in the winters of 1970, 1971 and 1972. A systematic sample of 41 transects was established to sample an area of 6150 sq. km. Each transect, located at the center of a standard 7 1/2-minute topographic map, was 8 km in length and approximately square in shape. Coverage began at local sunrise on any one day from 15 January to 15 February, and was completed in exactly 4 hours. Birds seen or heard within one-fourth mile (0.40) km were recorded separately for each hour, and those identified at a greater distance were entered in a separate column. The mean number of species per route was 29. Ten species showed a statistically significant change from 1970 to 1971 and 8 from 1971 to 1972. The Winter Bird Survey results were compared with the results from the Audubon Society's Christmas Bird Count in the same area. Close correlation was found between the two surveys, but in general the Winter Bird Survey totals are higher except for species that frequent feeding trays and those that are conspicuous along roadsides. The Winter Bird Survey method shows much promise as a means of world-wide monitoring of bird populations; it is urged that field tests be conducted on other continents.