Are Birds Increasing in Numbers?

Abstract

In an attempt to determine whether bird numbers are increasing, Marvin (1964) used the most available source, a nationwide bird survey published on all species, namely the Audubon Field Notes annual issues of The Christmas Bird Census (Cruickshank 1962–64; Robbins 1949). My purpose in writing this article is not to refute or affirm) Marvin's premise that bird populations are increasing, but to suggest that the Christmas Bird Census may not be statistically reliable as an indicator of trends in the total bird population in the United States between 1949 and 1962.