The vast forests of the western Great Lakes region are important breeding grounds for a wide variety of bird species. According to a new report, it appears that their populations are relatively healthy.

The U.S. Forest Service recently released a 322-page study of three national forests in the region, tracking bird populations based on monitoring at more than 1,400 locations by about 700 birders who volunteered their time or worked as paid field researchers for more than 25 years. The report covers 17 years’ worth of data (1995-2011) and is one of the most comprehensive long-term analyses of bird populations in North America. The vast amount of data allowed researchers to correlate specific species to variables such as habitat and climate in unprecedented detail.

According to the study, Chequamegon-Nicolet National Forest in Wisconsin and Chippewa and Superior National Forests in Minnesota support some of the most diverse groups of breeding birds in North America, particularly warblers, flycatchers, and thrushes. Together, the forests total more than five million acres.

Overall, the analysis painted a fairly optimistic picture: Most species were either stable or increased over the study period, and although variations between the forests were noted, trends were generally consistent.

“It paints a picture of fairly healthy bird communities in these forests over two decades of surveys,” said lead author Gerald J. Niemi, a biology professor at the University of Minnesota-Duluth. “It shows that there is tremendous diversity of bird species in the region and emphasizes the importance of national forests to migratory and resident bird species.”

Niemi and his colleagues evaluated population trends for 98 of the 127 bird species that nest in forest or woodland habitats. Several species increased significantly, including Yellow-bellied Sapsucker, Blue Jay, Red-breasted Nuthatch, and Ovenbird. No species declined significantly across all of the forests, but several declined in more than one. They included Great Crested Flycatcher, Connecticut Warbler, Scarlet Tanager, Song Sparrow, and Evening Grosbeak. The study focused on forest species, as its methods were less comprehensive for species such as waterfowl and raptors.

The report also suggests that eliminating the most dramatic human impacts on the forests may in fact decrease avian diversity. Timber harvests, particularly clear cuts, creates swaths of open areas and, later, successional shrub-like habitat favored by many birds, including Eastern Kingbird, Gray Catbird, and Brown Thrasher. So without further harvesting, bird species that prefer mature forests, such as Ovenbird, Red-eyed Vireo, Black-throated Green Warbler, and Black-and-white Warbler, may increase while those that prefer open or successional habitats would decrease. The overall impact would likely be reduced species diversity.

The study also identifies eight species “that potentially need special attention based on regional or global population declines” — Olive-sided Flycatcher, Magnolia, Connecticut, Golden-winged, and Yellow-rumped Warblers, Swainson’s Thrush, Boreal Chickadee, and Scarlet Tanager.

The report is significant for its findings on long-term regional bird populations but it also highlights the importance of the National Forest System to many bird communities. The analysis will also help inform management of national forests in the region, as birds are indicators of overall forest health. Of course, they also play important ecological roles, including seed dispersal and insect control.

The report will serve as a useful reference for forest managers identifying how species respond to forest management and what species need attention. — Jason A. Crotty

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Originally Published August 10, 2016