Northern Prairie Wildlife Research Center
To properly focus management resources, it is necessary to identify species and habitats in greatest need of management attention. For this purpose, we developed criteria to establish need and then ranked both birds and habitats accordingly.
Of the 40 bird species that require grasslands or a grassland habitat setting for some part of their breeding cycles, not all species are equally deserving of management concern. The following criteria take into account the species' status at a variety of scales, ranging from the species' entire range (global), the Upper Midwest (regional), Wisconsin, Wisconsin's natural divisions, and local sites.
We ranked all 56 grassland bird species (40 species requiring grasslands, plus 16 generalists that commonly occur in grasslands) using these criteria. We allowed a possible "score" of 1-5 for each criterion, with 5 indicating the highest management need. Criteria marked with a bird icon above were weighted more heavily than the others because we felt they were the most important for establishing management need in Wisconsin. We arrived at a final score for each species by summing the individual scores. Table 3 lists the 56 grassland bird species in ranked order, indicating the score, state status, and long-term monitoring needs for each species.
Species scored high in the ranking process for different reasons. For example, Henslow's sparrow scored high for almost all criteria, while bobolink scored high primarily because of consistent range-wide population declines and because it has a large population in Wisconsin compared with many other states. Sedge wren ranked high because it is a habitat specialist, it is relatively abundant in Wisconsin, and Wisconsin is in the center of its range. Brewer's blackbird scored low for most criteria except for a significant population decline across the entire continent and also because we lack knowledge about its ecology and management.
Of the top 25 species, we initially identified 23 as "species of management concern" (Table 3). They are all native grassland birds and all require grasslands during the breeding season. The remaining two species in the top 25red-headed woodpecker and orchard orioleare clearly deserving of conservation attention, but they are not species that require grassland habitats. They are species that were historically characteristic of savannas but that are now generalists found in a variety of habitats. In addition to the initial 23 species of management concern, we included three morenorthern harrier, Brewer's blackbird, and barn owlfor a total of 26 species. Northern harrier is an area-sensitive species that has generated concern among field ornithologists, in spite of its increasing trend on BBS routes. We know little about Brewer's blackbird, which expanded its range into Wisconsin relatively recently, but it appears to be area-sensitive and is dependent upon grasslands in this state. Barn owl is one of two state-endangered grassland birds in Wisconsin (along with loggerhead shrike). It is a rare, area-sensitive species whose status is poorly known in the state (Matteson and Petersen 1988). These three species, in addition to the top-ranking 23 species that require grasslands, are shown in bold in Table 3. Figure 2 shows population trends for species of management concern for which adequate BBS survey data exists.
The species of management concern reflect the full continuum of habitat structure required by grassland birds in Wisconsin, and they demonstrate the need to maintain a diversity of habitat types for the conservation of grassland bird populations in the state; no one or two habitats will accommodate the needs of all species of management concern. Even the top ten species of management concern in our ranked list encompass a wide variety of habitat preferences, such as:
Although the 26 species of management concern are listed in ranked order in Table 3, we do not suggest that management effort should focus only on the highest-ranked species. The lower-ranked species are also important for management focus and should not be allowed to "fall through the cracks" while we implement grassland management across the state. This list should be viewed as one of several tools for helping to focus conservation activities (Herkert et al. 1996).
We ranked grassland bird habitats based on three major criteria:
By managing for high priority habitats, managers can provide for the habitat needs of all high priority grassland bird species. Note that there are no habitats in categories 3 (important to birds, uncommon, and secure) or 5 (important to birds, common, and secure), revealing that no habitats that are important to grassland birds are secure, whether uncommon or common. The habitats of greatest value to birds are all in the vulnerable categories, and all native habitats are in the uncommon category.
Because habitats are ranked based on their importance to grassland birds, the rankings do not accurately reflect the value of those habitats to other bird species and communities. For example, while sedge marshes rank lower than sedge meadows and other habitats in their importance to grassland birds, they may be of great importance to some wetland species of conservation concern, including black terns.
High ranking habitats include both native and surrogate grasslands. A variety of factors contribute to their value:
Short and medium-height idle cool season grasses and forbs, which are typically composed of non-native species, rank very high. Fields of this habitat type are usually less expensive to establish than native warm-season grasses and forbs. However, to promote overall biodiversity we should expand, improve, and buffer remnants of native grassland vegetation, including native cool-season and warm-season grasses, or encourage large-scale restorations when feasible.
species of management concern use the full range of grassland bird habitat
structure, and they demonstrate the need to maintain a diversity of habitat
lower-ranked species are also important for management focus and should
not be allowed to "fall through the cracks."
habitats of greatest value to grassland birds are all vulnerable, and
all native habitats are uncommon.