Bird Population Trends in Minnesota and Northwestern Wisconsin Forests, 1991-1997

Abstract

The status of forest birds has been the subject of considerable interest (Terborgh 1989). Longterm monitoring can be used to identify species at risk by providing information on abundance patterns. We previously summarized our results on bird population trends in the Chippewa and Superior National Forests (NF), Minnesota, after three years of monitoring (Hanowski and Niemi 1994). In both forests, the Gray Jay, Winter Wren, Nashville Warbler, and American Redstart increased significantly and the White-throated Sparrow and Red-eyed Vireo decreased significantly. We also looked at population trends of breeding birds in Minnesota and Minnesota forested regions over the past 28 years using data from the North American Breeding Bird Survey (BBS), a continental monitoring program which uses roadside counts to sample breeding birds (Sauer et al. 1997) (Niemi et al. 1995). Forty-two percent of species (49 species) examined had no significant change in abundance,'36% (42 species) had significant increases, and 21% (25 species) had significant declines. Most species with declining trends could be grouped into three broad categories: species associated with forests, species of agricultural landscapes, and species associated with wetlands. In 1997, we completed the seventh year of our forest breeding bird monitoring program. Since the program’s initiation in 1991, we have added three study areas: the Chequamegon NF of northwestern and central Wisconsin, and Minnesota’s St. Croix River Valley (St. Croix) in 1992; and southeastern Minnesota (Southeast) in 1995 (Figure 1). Northern Minnesota and northwestern Wisconsin are located in the southern boreal-northern hardwood forest border (Pastor and Mladenoff 1991). Much of the conifer forest has been converted to aspen and birch since the middle of the last century (Coffin and Pfannmuller 1988). The present landscape has fewer conifer stands and more deciduous stands such as aspen and birch (Green 1995). Southeast Minnesota and central Wisconsin (southern most extent of the Chequamegon NF) are part of the eastern deciduous forest. Forests in this region have been altered by agricultural development or urban growth (Coffin and Pfannmuller 1988). We are currently monitoring five study areas by conducting over 1600 habitat-specific point counts each breeding season (Howe et al. 1997). Our objectives are to (1) identify species that have significant population trends for each study area; (2) identify species with significant population trends over the region; and (3) compare our results to trends from Minnesota BBS.