The effects of census date on the results of intensive Common Birds Census surveys

Methods for measuring populations of small, diurnal forest birds.

“…Even though seasonal changes in detectability have been documented in only a few cases (for example, Jarvinen and others 1977, O'Connor 1980, Weber and Theberge 1977, it is a potentially serious bias that must be considered. Consequently, field techniques that allow for detectability coefficients are required.…”