Experimental Design Considerations for Establishing an Off-Road, Habitat-Specific Bird Monitoring Program Using Point-Counts

We established bird monitoring programs in two regions of Minnesota: the Chippewa National Forest and the Superior National Forest. The experimental design defined forest cover types as strata in which samples of forest stands were randomly selected. Subsamples (3 point counts) were placed in each stand to maximize field effort and to assess within-stand and between-stand variation for a variety of bird parameters. Data gathered in 1991 were used to evaluate several assumptions that were made in the experimental design and showed that variance of most bird parameters among strata were similar. This data indicated that a proportional stratified sample by forest cover type was reasonable. We also found that two subsamples per stand would be optimum when a variety of strata types and bird variables were considered. Analyses based on 120 stands in the Chippewa National Forest and 150 stands in the Superior National Forest indicated that a two-tailed t-test could detect a 25 percent change in bird numbers for common species. For most other species, we could detect less than a 50 percent annual change. Monitoring programs within regions should be habitat specific so that changes in bird numbers can be related to: (1) habitat changes that have occurred in the region; (2) natural fluctuations in bird numbers; or (3) other factors. We recently suggested guidelines for determining the number of samples and size of study areas required for monitoring bird populations using line-transects (Hanowski and others 1990). We present a similar statistical approach to suggest an experimental design for establishing bird monitoring programs using point counts. An experimental design for determining monitoring programs in a region will be influenced by the objectives and resources available for each region. We assumed that the primary objectives of a monitoring program would be to: (1) monitor relative abundance of common bird species to assess annual changes, (2) define avian habitat relationships, (3) determine how forest management activities influence breeding bird abundance and distribution, and (4) provide a product that a regional wildlife biologist could use to plan forest management activities to accommodate a variety of bird species, especially those with specific habitat needs or declining populations in a region. Our objectives here are to: (1) describe in detail the methods that we used to establish a habitat-specific bird monitoring program in two regions of northern Minnesota, (2) present results of statistical aspects of the experimental design in terms of sample stratification and allocation of samples and subsamples, and (3) describe an observer training and testing program that will provide quality assurance in the data collection. 1 An abbreviated version of this paper was presented at the Workshop on Monitoring Bird Population Trends by Point Counts, November 6-7, 1991, Beltsville, Maryland. 2 Research Fellow and Director, respectively, Center for Water and the Environment, Natural Resources Research Institute, University of Minnesota, Duluth, 5013 Miller Trunk Highway, Duluth, MN 55811 USDA Forest Service Gen. Tech. Rep. PSW-GTR-149. 1995 Study Areas and Methods We established bird monitoring programs in two areas in Minnesota. The Chippewa National Forest is located in the north central portion of the State, and the Superior National Forest in the northeastern region. Major habitat types are similar within each Forest with the exception that upland spruce-fir (Picea sp. and Abies balsamea) forests are more common in the Superior National Forest.