Northern Prairie Wildlife Research Center
Although the BBS is the best source of quantitative data on trends of breeding bird populations in the midcontinent, the BBS has several limitations, including sparse coverage in central North America and biases associated with roadside surveys. Several studies have attempted to verify population trends from the BBS with data from independent, long-term surveys (e.g. Breeding Bird Atlas: Robbins et al. 1989; checklists: Temple and Cary 1990; Christmas Bird Count: Hagan 1993; migration counts: Dunn and Hussell 1995). Parallel trends derived from studying the same populations in different ways may provide corroborating evidence and strengthen the assessment of population trends of the BBS. Compared with eastern deciduous forests (e.g. Johnston and Hagan 1992), however, long-term data sets on breeding bird populations in the midcontinent are scarce.
Though a paucity of comparative information exists in the midcontinent, historic surveys provide an often overlooked source of baseline data on breeding bird populations (e.g. Graber and Graber 1963). These include the extensive survey of breeding birds in North Dakota conducted by Stewart and Kantrud (1972) in 1967 to obtain estimates of statewide breeding bird abundances and frequencies of occurrence. Data from the Stewart-Kantrud survey provided a unique opportunity to evaluate changes in breeding bird populations in the northern Great Plains. In 1992 and 1993, we repeated the Stewart-Kantrud survey using the same sample units and methods. Our objectives in this paper were to (1) examine changes in breeding bird populations in North Dakota; (2) compare patterns in breeding bird population changes with trends from the BBS; and (3) assess the likelihood that population changes may be influenced by changes in land use in North Dakota.