Northern Prairie Wildlife Research Center
So wrote the co-author of Birds of Wisconsin (Kumlien and Hollister 1903) in reaction to the changes in land use and bird populations he had witnessed since 1888 in southeastern Wisconsin. Yet his comments have meaning for us today, over 75 years later. Many an older farmer in Wisconsin can remember times when farmland birds such as meadowlarks, bobolinks, and upland sandpipers1 were much more common than they are today. These same people wonder what has happened to the cheerful avian denizens of their farmland "backyards."
In the 1970s and early 1980s professional and amateur ornithologists again voiced concerns over declines in grassland bird populations in Wisconsin (Hine 1973, Robbins 1982). The declines were confirmed by data from the U.S. Department of the Interior's Breeding Bird Survey (BBS). Between 1966 and 1994 the populations of ten grassland bird species declined significantly on Wisconsin's BBS routes, a higher proportion of species than in any other habitat guild2 (Robbins et al. 1996). These declines were not only evident in Wisconsin but were widespread throughout the Midwest (Herkert 1995) and the continent as a whole (Knopf 1994). In addition, the Partners in Flight Watch List includes 13 Wisconsin grassland bird species considered to be of high conservation concern (Carter et al. 1996).3 Sixteen grassland bird species occurring in Wisconsin were also recently identified as species of management concern in Region 3 by the U.S. Fish and Wildlife Service (USFWS; Office of Migratory Bird Management 1995).4
The causes for these population declines are especially difficult to determine for grassland birds, whose populations are known to naturally fluctuate both geographically and over time (Emlen and Wiens 1965, Cody 1985). However, the alteration and loss of breeding habitat are suspected causes (Robbins et al. 1996). Native grasslands have been almost completely lost since European settlement, and agricultural land has undergone many changes, from the era of wheat farming in the late 1800s, to the dominance of dairy farming in the mid-1900s, to the growth of row cropping in recent decades (Sample 1989). Some bird species adapted well to agricultural land use in the early to mid-1900s, but since the late 1950s large acreages of pasture and small grain crops have been converted to row crops, which decreased useable agricultural habitat for grassland bird species (Graber and Graber 1963). Also, much late-harvested grass hay has been converted to alfalfa, which is harvested early and frequently, causing significant mortality of nesting birds (Frawley 1989, Bollinger et al. 1990, Igl 1991). The loss of hay and pasture acreage is strongly correlated with declines in grassland bird populations in the Midwest (Herkert et al. 1996).
Other factors that may play a role in population declines are inadequate reproduction due to nest predation, brood parasitism, exposure to toxic chemicals, and excessive overwinter mortality caused by factors including changes or loss of habitat on migration routes or wintering grounds (Temple 1988). Changes in breeding distribution, such as shifting or contracting ranges, are also potentially related to population declines. We can detect these range changes for species that are at the edge of their breeding ranges in Wisconsin, such as Brewer's blackbird. However, these changes may stem from many different causes that are difficult to determine and may be related to conditions nearer the center of the species' breeding range.
Reproduction problems such as predation and parasitism are often related to habitat changes, although this is a topic that is poorly understood. When agricultural development fragmented the original grassland and grassland/savanna landscapes, it increased the amount of linear edge (Addis et al. 1995) and woody vegetation, which directly influences predator populations and movements. The number of buildings and farmsteads in a landscape may also influence predator population size and movements.
Ideally, management strategies should be based on an understanding of where and how a given declining bird population is limited at any time or place in its annual cycle, including geographically remote factors such as problems on the wintering grounds in the southern U.S. and Central and South America, which have received increasing attention in recent years (Lymn and Temple 1991, Basili and Temple 1995). However, information on most species is woefully inadequate for such a task, and decisions must often be based on educated judgment. Given the magnitude of changes in breeding habitats, habitat management on breeding grounds is generally a prudent course of action. It is likely to benefit at least some bird species that are limited by the availability or quality of breeding habitat, and is not likely to have negative impacts on species that are limited elsewhere.
Although grassland birds face challenges to their survival that are different and perhaps more numerous than at the end of the last century, we can through habitat management, help improve their chances in the century before us.
1966 and 1994 the populations of ten grassland bird species declined significantly
on Wisconsin's Breeding Bird Survey routes, a higher proportion of species
than in any other habitat group.