Standardized morning and afternoon counts were conducted in two deciduous forest plots during seven winters. Morning counts yielded more species than afternoon counts, as well as higher counts of most species. A minimum of eight visits is recommended. Six visits yielded 2% to 5% fewer species, depending on the size and bird population of the study plot. Cumulative means for individual species varied erratically for most species when the number of visits was less than seven.
Additional publication details
Reappraisal of the Winter Bird-Population Study technique