Two-hundred twenty-nine bird species breed in the MH/TGP ecosystem, including 30 resident species, 23 migratory species that develop some resident populations, 13 migratory species for which the region is primarily a migration stop-over, 161 migratory species that breed extensively in the MH/TGP ecosystem, and 2 recently re-introduced species (Table 3). The piping plover and Henslow's sparrow are the species of greatest management concern (Table 3). Fifteen species (7%) are classified as High Priority, 47 species (21%) as Priority, and 54 species (24%) as No Score Available (Table 4). Species for which no score was available are listed in taxonomic order at the end of Table 3.
Grassland is the habitat of highest concern followed closely by shrub-sapling and wetland (Table 4). Wetlands host the most breeding bird species, (36) followed closely by lakes (32) and mature deciduous forest (30). No concern scores are available for a large proportion of species in two of the highest concern habitats, wetlands (22%) and lakes (31%) , and, although mature coniferous forest is ranked tenth in priority, concern scores are not available for almost half (44%) of its 27 breeding species (Table 4).
BBS trend data for Minnesota or the BBS Central Region were available for 183 species (Table 5). In Minnesota, 15 species have significant negative trends and 34 species have significant positive trends. In the whole BBS Central Region, however, 35 species are experiencing significant population declines and only 25 species are experiencing significant increases (Table 5). Of particular interest to managers in the MH/TGP ecosystem are the Swainson's thrush, loggerhead shrike, Bell's vireo, northern parula, prothonatory warbler, and lark sparrow, all of which have no trend information available for Minnesota, but have significantly decreasing trends in the BBS Central Region. The pileated woodpecker, orchard oriole, and chestnut-sided warbler have significant positive trends in Minnesota, but significant negative trends over the entire BBS Central Region (Table 5).
Habitats | Habitat fragmentation | Cowbird parasitism | Winter habitat | Research and monitoring
Many publicly owned wildlife areas in the tallgrass prairie part of the MH/TGP ecosystem have been largely invaded by woody species. Although these areas could be managed for woodland species of concern, it is unlikely that such management will contribute much to overall populations of woodland species. We suggest that management of these areas should be oriented towards protecting and restoring the most natural ecosystem possible, in most cases a prairie or prairie/wetland complex. As a consequence, the biodiversity of the MH/TGP ecosystem and the north-central United States will be protected, although local species richness may not be maximized. This could meet resistence by some local groups, and compromises may need to be reached such as limiting woody species to riparian habitats.
A second example is the existence of fragmented grassland tracts within forest complexes in the eastern deciduous biome, most likely a result of agricultural activities. Although grasslands are a high priority habitat, these isolated tracts are likely to remain marginal production areas or even population sinks for grassland birds no matter how much effort is expended, and they might also be detrimental to area-sensitive forest-interior species. The best management strategy may be to allow these grasslands to follow succession into forest habitat, increasing total forest area and decreasing forest fragmentation.
These examples are just two of the possible senarios managers could face when trying to determine for which habitat type(s) they will manage. Each management team must consider their own resources, determine their goals for management, assess public opinion, and work with the entire landscape when developing a management plan.
Habitat fragmentation. Habitat fragmentation has been cited as a primary reason for the decline of many forest and grassland songbirds (e.g., Wilcove 1985, Askins 1993). Many species have minimum-area requirements and seldom use small or isolated habitat fragments, including Henslow's sparrow, northern harrier, upland sandpiper, cerulean warbler, yellow-throated vireo, hooded warbler, and the veery, all classified as High Priority or Priority species in the MH\TGP ecosystem (Sampson 1980, Lynch and Whigham 1984, Askins et al. 1987, Robbins et al. 1989, Herkert 1994a). Other species will occasionally use isolated or small patches of habitat although densities are relatively low compared with large continous tracts of habitat (Lynch and Wigham 1984, Askins et al. 1987, Herkert 1994a).
Not only will many forest-interior or grassland species avoid small habitat patches, but when they do breed in these patches, reproductive success is low. This is most likely because small habitat patches have a large proportion of forest edge where rates of predation on eggs and nestlings, and brood parasitism by brown-headed cowbirds, is up to three times greater than in the forest or grassland interior (e.g., Gates and Gysel 1978, Wilcove 1985, Small and Hunter 1988, Temple and Cary 1988, Johnson and Temple 1990). It is not unreasonable to believe that many species within wetlands, lakes, or other habitat types are also negatively affected by edge (e.g., Brown and Dinsmore 1986).
The detrimental effect of habitat fragmentation is contrary to the long-held management tenet that habitat heterogeneity benefits wildlife through the edge effect. Although increased edge habitat can increase local bird species diversity by providing habitat for generalists and forest-edge species, it excludes many forest-interior and grassland species (Robinson 1988). Similarly, some researchers have proposed that several small sites may contain more species than a single large one of equal area, and thus may be more effective as wildlife preserves (Simberloff 1982, Simberloff and Abele 1976, 1982, 1984). Again, a distinction must be made between generalists that will persist with or without management consideration and specialists dependent on large tracts of forest interior or grasslands for which no number of isolated tracts can make a difference. Management of large habitat blocks for area-sensitive species will help ensure their survival and will not result in the loss of edge species in the MH/TGP ecosystem, where agricultural land use patterns ensure abundant edge habitat.
If managers are to conserve the biodiversity of the MH/TGP ecosystem, large tracts of continuous habitat must be provided. We give specific suggestions for improving the "effective area" of different habitats throughout the management recommendations section of this paper. In general, however, habitat patches as large as possible should be conserved or restored, patch shape should approximate a square or circle to reduce the edge/interior ratio, management practices such as "wildlife clearings" should be eliminated from larger forest habitats, and habitat patches should be as close to other similar habitats as possible to reduce isolation.
Cowbird parasitism. Whether brown-headed cowbird parasitism is a major cause of declining populations of some bird species or not is a point of controversy, but either way, parasitism poses a threat to many species of concern by lowering nest success and breeding productivity (Mayfield 1977, Brittingham and Temple 1983, Robinson et al. 1995). The most effective and permanent method of reducing the impact of cowbird parasitism is through landscape-level habitat management (Robinson et al. 1992). Suggested management practices are:
1) Reduce edge. Cowbird parasitism is highest near wooded edges and small woodlots (Brittingham and Temple 1983, Johnson and Temple 1990, Robinson et al. 1995). Increasing habitat patch size, reducing forest fragmentation, and reducing edge in grasslands and forest habitats will help reduce the impact of cowbird parasitism on species of concern.
2) Eliminate or reduce cowbird feeding opportunities (bare ground, short grass, pastures, feedlots, campgrounds, cultivated fields) "near" woodlands being managed for forest birds [Cowbirds have been known to travel up to 7 km from feeding areas to breeding areas (Thompson 1994)]. Do not mow roadsides or campgrounds in large forest tracts, or if this is not possible, keep vegetation at a height of 6 to 9 inches or more to reduce its suitability as cowbird feeding areas. Limit the width of and revegetate logging roads, avoid feeding cowbirds, reduce or disallow grazing, and close or avoid creating new corrals and packstations (Robinson et al. 1992, Herkert et al. 1993).
3) Eliminate tall perches (>1.5 m) from areas managed for grassland birds. Female cowbirds use trees, telephone poles, and other tall perches to scout potential host nests (Norman and Robertson 1975, Thompson and Gottfried 1981) and may be unable to gather enough information on the status of potential host nests to lay at an appropriate time in treeless environments (Freeman et al. 1990). Remove wooded fencerows next to managed grasslands and avoid building and/or remove existing picnic shelters, telephone lines, flagpoles, billboards and signs, trees, recreational towers or equipment, etc. from grassland areas. If this is not possible, consolidate all tall structures into one area.
4) In forested areas managed for timber, low volume single-tree selection is recommended. If clearcuts must be used, the establishment of new edge should be minimized (Herkert et al. 1993).
5) In severely fragmented habitats where land management practices are not enough, trapping may be the only way to protect remnant populations of sensitive species (e.g., Shake and Mattson 1975). Such trapping is expensive and unproven for most host species and should be considered a last resort. See Robinson et al. (1992) for trapping strategies and cautions.
Winter habitat. The winter habitats of permanent residents are usually similar to their breeding habitats. Some noteworthy changes from summer to winter habitat include the type of water sought by waterfowl and the influence of winter bird feeding on the distribution of upland species. In winter, ducks and geese seek larger bodies of water to escape ice cover. They go only as far south as necessary and some will remain in the MH/TGP ecosystem during mild winters. Ring-necked pheasants move into wetlands for shelter or farmyards for food, sharp-tailed grouse move into dense shrub or roost in trees for shelter, while gray partridge remain in fields. Many forest species move into suburban areas, city parks, or shelterbelts to take advantage of winter bird feeding (Robbins 1991). The greater prairie chicken and the sharp- tailed grouse are the only High Priority and Priority permanent residents in the MH/TGP ecosystem, although concern scores are not navailable for most permanent residents.
Fifteen bird species winter in the MH/TGP ecosystem although they do not breed there (Table 6). Two of these species have high concern scores, the northern shrike (22) and Harris' sparrow (24). Concern scores are not available for the remaining thirteen species. Although it is beyond the scope of this report to give management suggestions for non-breeding species, managers should consider this for future study. Many of the MH/TGP ecosystem species of greatest concern are declining in part due to threats on the wintering ground (both neotropical and short-distance migrants) and may continue to decline if wintering grounds are not preserved or better managed. Likewise, species of management concern that winter in the MH/TGP ecosystem may continue to decline unless management of winter habitats is a priority.
Research and monitoring. The consequences of many management actions are unknown. In some cases, immediate effects are known but long-term ones are not. In other cases, effects on target species are understood, while influences on non-target species are not. Often experts cannot agree on the effects of a proposed management action. Although decisions must often be made with incomplete knowledge, research should be conducted on proposed management activities that are poorly understood, especially if 1) they influence large areas of land, 2) the land hosts High Priority species, or 3) the management action has dramatic effects. After implementing management actions, short- and long-term responses should be monitored to allow fine-tuning or re-evaluation of the action and to provide other managers with valuable, time and money-saving information.
Grassland is the highest priority habitat in the MH/TGP ecosystem with 9 of 21 breeding species (43%) in the High Priority or Priority concern classes (Tables 4, 7). Factors responsible for the decline in populations of grassland birds are not entirely understood, but are most likely a combination of loss and degradation of grassland habitat, reproductive failure due to high rates of nest predation and nest parasitism, pesticide contamination, and shifts in agricultural practices, such as increasing percentage of acres in rowcrop production and earlier and more frequent mowing of hayfields (Rodenhouse et al. 1992, Herkert et al. 1993). To retain the diversity of grassland species in the MH/TGP ecosystem, we must intensify management efforts and improve current management practices.
Management for grassland birds is difficult and complex. Because grasslands depend on disturbance to persist, habitat that is suitable for a species one year may have become unsuitable by the following year. Moreover, each grassland species has unique habitat requirements, and management that favors one species may preclude another. In the following section we review the specific habitat requirements and response to common management practices of High Priority and Priority grassland species in the MH/TGP ecosystem. The grasshopper sparrow is included in this review because it is at the top of the Concern class, has a significantly declining population trend in the Midwest, and has been included on at least two regional lists of species of special concern (Table 3). Following this species review, we give specific management recommendations for grasslands, concentrating on the species of highest concern.
Most High Priority or Priority grassland species in the MH/TGP ecosystem are sensitive to fragmentation (Table 8). Although minimum area estimates and tolerable degree of isolation vary greatly by species and region, all fragmentation-sensitive species need large tracts of high quality grasslands to maintain breeding populations. Herkert (1994b) found that habitat area had a much greater influence on breeding bird composition than even management techniques such as burning. To effectively manage for grassland species of concern, large tracts of grassland will need to be conserved or restored.
Seven of the eight tallgrass prairie species (88%) require "older," well-established grassland (Table 8). Most prefer tall, dense cover, many need standing dead residue or forbs for perching, singing, or nest sites, and two species, the northern harrier and sharp-tailed grouse, prefer some low shrub growth for nest sites or winter cover. The two mixed-grass prairie species, the chestnut-collared longspur and Sprague's pipit, only occur in the western counties of the MH/TGP ecosystem where mixed-grass prairie characteristics (short, sparse grass and well-drained soils) can be approached. Most High Priority or Priority grassland species (tall and mixed-grass) need a mosaic of habitat conditions and grass heights in the same area (Table 8). Population densities are much lower in monocultures and most species prefer native grasslands (Kirch 1974, Kirch and Higgins 1976, Wilson and Belcher 1989).
Prescribed rotational burning is the recommended management technique for grassland maintenance. Only the upland sandpiper responds positively in the first growing season after a burn, but all species respond positively within 3-5 yrs (Table 9). Johnson and Temple (1990) found lower predation rates for all species combined on recently burned prairie, and nest success is higher for some species 2-3 yrs after a burn (Kirsch and Higgins 1976). The common burn interval of 3-4 yrs, however, may be too short. Most High Priority and Priority species are still responding positively 5 yrs after a burn and a few, the northern harrier, Henslow's sparrow, and sharp-tailed grouse, are known to respond positively or maintain pre-burn populations in areas that have not been burned for 10 yrs. We suggest a minimum 4 yr interval between rotational burns, with a 5-6 yr interval preferred, on all prairie tracts large enough to maintain high priority species (80 acres).
If burning is not possible, light to moderate deferred grazing (after Aug. 15) every 3-5 yrs is the second best management choice followed by mowing or haying after Aug. 15 every 3-5 yrs (Table 9). Again, 4-6 yr intervals may be more beneficial for both practices. Because so little is know about the effects these management systems have on grassland birds in this ecosystem, however, careful research and monitoring should be conducted if either of these options are chosen. All species are negatively affected by heavy grazing or grazing during the breeding seasons, and annual burning, mowing, or grazing is detrimental to all species except upland sandpipers (Table 9).
The following recommendations are given with the goal to maximize diversity and persistence of grassland bird populations across the entire MH/TGP ecosystem, although they may result in a decrease in local species richness. Grasslands that may be managed effectively for species of concern include prairie (natural and restored), seeded grassland ("wildlife areas"), light to moderately grazed pasture, Conservation Reserve Program (CRP) land, and hay fields not mowed before July 15. Cultivated rowcrops and hayfields mowed before July 15 provide poor habitat for nesting birds and/or may serve as ecological traps by attracting birds to nest in areas where productivity is low (e.g., Rodenhouse and Best 1983, Best 1986, Warner and Etter 1989, Bollinger et al. 1990, Stallman and Best 1996).
Grassland management recommendations where wildlife conservation is the primary goal.
1) Avoid fragmentation of existing grasslands. The preservation and proper management of existing grasslands, especially those used by priority species, is the most effective means of conserving grassland birds.
2) Birds readily colonize restored grasslands or prairies, especially in areas where breeding populations already exist (Higgins et al. 1984, Volkert 1992). A mixture of native warm season grasses is best although a few native cool season grasses could be added to the mix. Recommended tall grasses include big bluestem, indian grass, and switch grass. Recommended short grasses include little bluestem, side oats gramma, and prairie dropseed (Herkert et al. 1993). Include forbs in the seed mix or reduce grass seeding rates by up to 50% to encourage "volunteer" forbs (Sample and Mossman, unpubl. data). Avoid monocultures (e.g., Kirch 1974).
3) Grassland restorations aimed at benefiting High Priority and Priority species should be at least 125 acres and preferably more than 250 acres (Herkert et al. 1993), although smaller plantings of less than 50 acres could benefit the dickcissel and other grassland species not sensitive to fragmentation. Fields smaller than 20 acres are only acceptable when located next to other grassland habitat, such as pasture, so the combined acreage is more than 40 acres (Sample and Mossman, unpubl. data).
4) When 50 acre or greater contiguous restorations are not possible, establish several smaller scattered restorations. Individual patches should be at least 20 acres and preferably located within a mile of each other. Take advantage of grassed waterways, roadsides, CRP, and grainfields to provide non-woody edge and corridors between patches. Roadsides adjacent to grasslands or used as corridors should be free of woody vegetation and managed as part of the grassland unit.
5) The effective size of a prairie restoration can be increased by locating it next to existing prairie, pasture, wetland, or hayfield. Even croplands provide a non-woody edge and grassland/shrub transition zones are preferred over woodland edge as they can provide valuable habitat for sharp-tailed grouse, northern harriers, and some shrub and agricultural-woodland edge species of concern such as Bell's vireo and the loggerhead shrike. Remove all woody vegetation between the restoration and pasture or cropland. To achieve maximum benefits, the highest structures between habitats should be low fence posts.
6) Design grassland plantings to minimize the amount of linear edge (Herkert 1994a). While circular plots are ideal, square plots are often more practical in agricultural landscapes and are preferred over rectangular plots of the same area. Avoid restorations with very irregular borders.
7) Consider the greater landscape when planning restorations. Smaller scattered plantings may be beneficial in areas with extensive pasture, CRP, or grassland preserves. In areas that are largely urbanized, wooded, or cultivated, however, large tracts of quality grassland would be required to have much impact on bird populations (Sample and Mossman, unpubl. data).
8) Avoid shelterbelts, tall fences, telephone lines/poles, and areas with abundant human activity such as homes, farmsteads, campgrounds, or picnic areas, when planning restorations. Remove any structure taller than the average grass height in established or restored grasslands, including signs, picnic shelters, or recreational towers.
9) Recreational trails should be located only around the edge of the prairie because nesting success and nest density decrease the closer the nest is located to a trail (Miller and Knight unpubl. data). Grassland birds are audible and visible from a distance and supplemental plantings around trails can provide adequate viewing of prairie vegetation.
10) Scattered small shrubs may benefit some grassland species and grassland-shrub transition zone species, although they are detrimental to others. Keep shrubs to the edge of grasslands or in riparian zones. Woody cover should compose less than 5% of grassland habitat (Sample and Mossman, unpubl. data).
11) Where grasslands border forested tracts, allow prescribed fires to burn slowly through the forest edge. This technique creates a more natural, open edge as opposed to a sharp wall of woody vegetation. Such "feathered edges" have lower nest predation rates than sharply contrasting edges (Ratti and Reese 1988).
12) Prescribed burning in early spring (March to early April) or late fall (Oct. to Nov.) is the best way to maintain high quality grasslands. Grassland areas larger than 30 acres should be burned on a rotational system with some subunits (50-100% of entire area) left idle each year. No more than 20 - 30% of large grasslands (>100 acres) should be burned in a year. Management units should be 20-30 acres. (Zimmerman 1988, Herkert 1994a).
13) Smaller grasslands can be managed as one unit. When several small grasslands are grouped in one area, coordinate burn schedules so only a small percentage (20%) are burned each year.
14) We recommend subunits should be burned no more than every 4-6 years, especially on grasslands large enough to support high priority species (>80 acres) or in areas where abundant nearby pasture can provide short grass nesting opportunities (Zimmerman 1988, Herkert 1994a).
15) Deferred grazing or mowing/haying after August 15 to maintain grassland habitat should only be considered if burning is not feasable, with grazing preferred over mowing/haying (Table 9). As with burning, grasslands should be grazed and mowed on a rotational basis every 4-6 years, with at least 75-80% of total area left idle each year. Avoid cutting prairies very late in the growing season because this adversely affects plant species composition and growth and encourages invasion by non-native problem grasses such as Kentucky bluegrass (Launchbaugh and Owensby 1978). Light grazing (40% or more vegetation cover at 10 inches in height) is preferred over moderate grazing (20-40% vegetation cover at 10 inches). Heavy grazing should be avoided at all times (Table 9).
Grassland management recommendations for private land owners interested in wildlife conservation where agricultural production is the primary goal.
1) Avoid cutting hayfields before July 15 (e.g., Bollinger et al. 1990, Sample and Mossman, unpubl. data). If possible, delay cutting until August 1 with August 15 cuttings optimal. Consider seeding hayfields with a mixture of warm-season grasses.
2) Bird species richness decreases as grazing pressure increases. Deferred grazing (after July 15) is preferred over rotational grazing, while rotational grazing is preferred over continous grazing. Heavy grazing pressure is detremental to all High Priority and Priority species in the MH/TGP ecosystem (Table 9).
3) A "bird friendly" rotational grazing system requires moving livestock frequently, leaving > 4 inches residue, grazing alternate paddocks across pasture, and creating a refuge area at the center of the pasture for birds. The refuge area should be up to 1/3 of total pasture area, should be located away from buildings or edge, can be grazed until May 15, should defer grazing between May 15 and July 1 (July 15 would be optimal), and could be grazed as desired after July 1 to the end of season or cut for hay after July 15. Rotational systems produce higher quality forage, produce more successful nests, and attract more birds of more species than continous pasture (L. Paine, Univ. Wisconsin, pers. comm. ).
4) Roadsides adjacent to hay or small grain fields can provide important refuges for adult birds and recent fledglings during harvest (Camp and Best 1994). Do not mow roadsides before July 15 (Aug. 15 is optimal).
5) Plant CRP to a mixture of native warm season grasses when possible including forbs in seed mix. If non-native grasses are used, plant a mixture of at least 3 grasses and legumes (Herkert et al. 1993, Sample and Mossman, unpubl. data).
Shrub-sapling is the second-highest-ranking habitat of management concern in the MH/TGP ecosystem (Table 4). Twenty-one species use shrub-sapling as their primary habitat, eight of which are High Priority or Priority species (Table 10).
Like grassland specialists, shrub specialists depend on a habitat that is transitory: it quickly becomes unsuitable without continual disturbance or management. The decline in shrubland species' populations may reflect the loss of shrubby old fields in the MH/TGP ecosystem with the increased efficiency of agriculture and trends towards reforestation and urban/suburban growth (Confer 1992, Askins 1993). Loss of this habitat may also have occurred on managed lands if managers view shrub-sapling habitat as just a transition between two more desirable habitats, grassland or forest. Conservation of shrubland specialists may require deliberate management to maintain or create suitable shrub-sapling habitat.
The eight shrub-sapling High Priority and Priority species can be divided into three habitat management groups: Shrub-grass, Shrub-wood, and Shrub-riparian (Table 11). Four species are classified as Shrub-grass species. These species need shrub-sapling habitat in a landscape dominated by grassland, and they generally will invade an area at an early seral stage. Shrub-wood species (3) need shrub-sapling habitat within a more forested region and will continue to inhabit shrub-sapling habitat at later seral stages. One species, the Bell's vireo, is classified as shrub-riparian. Bell's vireos generally prefer open shrub-sapling habitat within a riparian zone or wetland.
All shrub-sapling High Priority and Priority species are dependent on a dense shrub layer, and most need complex vegetational structure within individual territories, including both open grass for nest sites or feeding, and taller shrubs or trees for perching and nesting (Table 11).
Shrub-sapling habitat should be managed according to the following general guidelines.
General management recommendations.
1) Shrub-sapling High Priority or Priority species are not as area sensitive as many forest or grassland species of concern (Askins 1993). Consider managing small parcels of habitat (1-40 ha) for shrub-sapling species instead of grassland or forest species.
2) Shrub-sapling species may be sensitive to edge effects. New habitat should have a high ratio of area to perimeter.
3) Large habitat blocks should also be set aside for the management of shrub-sapling species. Confer (1992) proposes a 40 year cycle of prescribed rotational burning to maintain shrub- sapling habitat. Habitat units should be 10 - 20 acres.
4) Do not drain bottomland hardwoods or shrub swamp areas. These are especially critical habitat for the American woodcock and Bell's vireo (Brown 1993, Keppie and Whiting 1994).
5) Do not mow or burn shrub-sapling habitat during the nesting season, 15 May - 15 August (Keppie and Whiting 1994).
6) Shrub species are especially vulnerable to flooding along riparian zones because their nests are often within a meter from the ground. Careful consideration should be given before large quantities of water are released from dams or reservoirs (Brown 1993).
Grassland-dominated landscapes.
1) Riparian zones within grasslands may be effectively managed for shrub-sapling species by increasing prescribed burning rotations, adjacent to streams and gullies, from 4-6 year rotations, to 10-20 year rotations. Shrub zones on either side of the stream should be approximately 100 feet wide. Shrub zones may improve stream water quality and will provide habitat for late successional grassland species, early successional shrub-sapling species, and the loggerhead shrike (Herkert et al. 1993).
2) Consider managing the area between forest edge and large grasslands for shrub-sapling species. Shrub habitat may provide a transition zone between forests and grasslands, decreasing the detrimental edge effect and increasing habitat for shrubland species. Units of habitat closest to grasslands can be burned on 10-20 year rotations, while units closer to or within the forest edge could be burned on 20-40 year rotations.
Forest-dominated landscapes.
1) Although it is detrimental to most grassland and forest interior species to try to maintain grassland habitat within small forest openings, it may not be detrimental to maintain shrub-sapling habitat within current openings. This could benefit shrub-sapling species and some gap-dependent forest species like the hooded warbler and the blue-gray gnatcatcher (Lynch and Whigham 1984, Gartshore 1988).
2) Most shrub-sapling habitat in the northern part of the MH/TGP ecosystem is second-growth forest following clear-cutting. Leaving residual standing live or dead trees, shrubs, and saplings within a clearcut increases the immediate habitat quality for shrub-sapling species and also increases habitat quality of the regenerating forest twenty to sixty years after cutting (Niemi and Hanowski 1984, Green 1995)
3) Clear-cutting (while leaving residual live vegetation) may be more beneficial to shrub-sapling species than uneven age or single selection cuttings (Keppie and Whiting 1994). Clear-cutting, however, is detremental to many forest interior species and should only be used as part of a carefully considered timber management plan. See the general forest management section for timber management recommendations.
4) Eliminate grazing along riparian zones and forest edges. Overgrazing suppresses shrub growth and reduces available nest sites for shrub-sapling species (Brown 1993).
Wetlands include wet meadows, fens, beaver ponds, and temporary, seasonal, semi-permanent, and permanent marshes, and are the third highest priority habitat in the MH/TGP ecosystem (Table 4). More species use wetlands as their primary breeding habitat (36) than any other habitat type in the MH/TGP ecosystem, including the highest number of High Priority (4) and Priority (9) species (Table 12).
Habitat loss is the main reason cited for the population decline of most wetland species (e.g., Gibbs et al. 1992, Tacha et al. 1992). Wetlands have been extensively converted for agricultural use in the MH/TGP ecosystem and only a small fraction of pre-European-settlement wetlands still remains. Habitat degradation also reduces population numbers. Eutrophication, siltation, chemical contamination, and human disturbance seriously reduce habitat quality, primarily by degrading food supply, even on large, protected wetlands (Gibbs et al. 1992). To manage wetland species effectively, managers must not only provide more wetland habitat, but also protect habitat quality in existing wetland complexes.
All High Priority and Priority wetland species in the MH/TGP ecosystem require intermediate to dense, emergent vegetation, or densely vegetated uplands (Table 13). Many species need diverse wetland types within the same complex, to provide habitat for nesting and brood rearing, or to provide adequate wet habitat all season. All High Priority and Priority wetland species, except the redhead, use at least two types of wetlands extensively, including seasonal wetlands (Table 13).
Wetlands cannot be separated from their adjacent uplands when determining an effective management plan. Dabbling ducks feed in wetlands, but usually nest in upland grassland. Certain shorebirds, such as Wilson's phalarope and the marbled godwit, likewise require terrestrial and aquatic habitats. American bitterns and northern harriers will nest in either emergent wetland vegetation or in dense upland vegetation. Yellow-headed blackbirds nest in wetlands, but often forage in terrestrial habitats, and some species, such as LeConte's sparrow, take advantage of wet periods to invade upland grass-forb plantings (Igl and Johnson 1995). Thus, management recommendations for wetlands include the entire prairie/wetland complex.
The following management recommendations are directed toward the landscape level or the desired outcome of specific management techniques, and they concentrate on integrating non-game management with common waterfowl management techniques. Garner et al. (1994) and Kriel et al. (1993) provide more specific information on specific management techniques and their effects on both game and non-game wetland species.
General guidelines:
1) Prevent drainage of existing wetlands (Greenlaw and Rising 1994, Johnson 1996). This may be achieved by purchasing in fee title, by buying easements that prevent drainage, by legal proscription, by tax incentives, or by encouraging wetland owners in numerous other ways (Kriel et al. 1993). Unaltered natural wetlands and upland habitats should have highest priority for protection.
2) Restore wetlands when possible. Restored wetlands provide habitat for a diverse community of bird species, especially as restored wetlands age (> 3 years). Restored wetlands usually lack the wet meadow zone found in natural wetlands, however, and researchers are uncertain how closely restored wetlands will come to resemble and function as natural wetlands, or how similar their bird communities will be. Protection of natural wetlands should be give priority over wetland restoration (Hemesath 1991, Delphey and Dinsmore 1993, VanRees-Siewert 1993).
3) Many wetland species may be area sensitive (Brown and Dinsmore 1986, Johnson 1996). Wetland restorations should be planned to increase the area of existing wetland complexes first, or to complement existing grasslands, second. Larger wetland complexes host a mosaic of habitat types, support greater species richness, and may decrease predation.
4) Wetland complexes should approximate a circle or a square to minimize edge effect and the subsequent predation and cowbird parasitism.
5) Upland grasslands surrounding wetland complexes should be managed according to the guidelines for managing grassland habitats. Prescribed burning to provide a mosaic of vegetation heights and densities is the preferred method of grassland management within wetland complexes. A 4 year or greater burn schedule should be used to ensure adequate tall, dense vegetation.
6) Do not burn, mow, or graze wetland complexes and adjacent uplands during the breeding season (15 April - 15 August). In emergency drought situations, uplands mowed after July 21 will only affect approximately 10% of nests that would have hatched that year (Duebbert and Frank 1984).
7) Control dense stands of emergent vegetation by burning, shallow discing, or mowing after basins have dried in late summer or early fall. Mowing vegetation over ice can also be used to reduce emergent vegetation and the litter will provide a substrate for invertebrates the following spring (Fredrickson and Reid 1986). If a marsh choked with cattails must be reconditioned in the summer, coordinate with a plan to reflood and manage for fall migrating shorebirds (see #12).
8) Maintaining the natural dynamics of wetlands is essential for maintaining their productivity and value as habitat for birds (Johnson 1996). Where water levels can be controlled, moist-soil management is recommended (e.g., Fredrickson 1991, Fredrickson and Taylor 1982, Reid et al. 1989). Moist-soil management not only benefits waterfowl, but also enhances the value of habitat for breeding and migrating shorebirds and other wetland-dependent species as well (Fredrickson and Reid 1986).
9) Allow wetlands to dry periodically. Drying of wetland basins facilitates nutrient cycling and results in high productivity when water returns (Murkin 1989).
10) Land acquisition programs should include a range of wetland types within a complex to provide resources during different stages of the precipitation and breeding cycles. Historically, state and federal acquisition programs have focused on semi-permanent and permanent wetlands for waterfowl management. Seasonal wetlands, however, are also used extensively by migrating and breeding waterfowl (Duebbert and Frank 1984). Moreover, seasonal wetlands and wet meadows are essential for most non-game wetland species of concern (Table 13), and are the wetlands most threatened by agricultural drainage or modification from tillage (Duebbert and Frank 1984).
11) Predation may be a serious problem in many wetland complexes, especially small or linear-shaped ones. Predator barriers, such as electric fences, have been used successfully in North Dakota (Mayer and Ryan 1991). Additionally, creation of islands on restored wetlands and conversion of peninsulas to islands are also successful in reducing predation (PPJV Shorebird Manage. Plan, Lokemoen and Messmer 1994). Wetland restoration in areas where nest success is low due to predation may also be counterproductive. Predator communities should be assessed before management activities are undertaken (Greenwood et al. 1995).
12) Consider managing a portion of wetland complexes for migrating and breeding shorebirds. Most manipulations will fit readily into current management plans, and benefit a wide range of migrating and breeding birds, including High Priority and Priority wetland and lake species. See Rundle and Fredrickson (1981), Eldrige (1990), and Helmers (1992) for more information on shorebird management.
13) Protect water quality of wetlands to ensure an adequate prey base (Gibbs et al. 1992, Storer and Nuechterlein 1992).
Lake habitat includes the Great Lakes and inland lakes, ponds, or streams with deep, open water and their adjacent shores and islands. Lakes rank fourth in management concern of the MH/TGP ecosystem's 13 primary habitats (Table 4), and host 32 primary breeding species, including 3 High Priority species and 7 Priority species (Table 14). Many lake species are often secretive in nature or sensitive to human disturbance, making them difficult to study. No concern scores were available for 10 lake species (31%). Further study of these species is needed to accurately access management strategies for lake habitat.
Lake species have a range of preferred habitat characteristics, although most need a large amount of open water within a grassland/shrub environment (Table 15). Only two Priority species depend on lakes within forested habitat. Most lake species are also extremely sensitive to human disturbance, especially at the nest site (Table 15). Those that are not sensitive to direct disturbance are often negatively affected by the increased predation, habitat loss, or pollution that accompanies human development (Gibbs et al. 1992).
General guidelines:
1) Protect existing lake habitat from further development.
2) Include seasonal and semi-permanent wetlands in the same management unit or wetland complex as larger, permanent lakes. A variety of wetland types is important for the marbled godwit and lesser scaup, and lakes may provide wetland species with the open water they need for rearing broods (Tables 13, 15).
3) Many lake species are extremely sensitive to direct human disturbance at nest sites (Table 15). Restrict human access to breeding islands and nesting colonies, including recreational skiers, boaters, swimmers, hikers, and anglers. Educational programs and signs may help ease tensions between recreational users and managers.
4) Maintain stable water levels in large, permanent wetlands with sufficient open water to sustain lake species. Intentional drawdowns for waterfowl and shorebird management are detrimental to many lake species and should only be practiced on smaller, semi-permanent or seasonal wetlands that do not support most lake species (Haig 1992, Burger and Gochfeld 1994, Mitchell 1994)
5) Upland grasslands surrounding lakes should be managed according to guidelines for managing grassland habitats. Prescribed burning to provide a mosaic of vegetation heights and densities is the preferred method of grassland management.
6) Mature forest buffer zones of 100 - 200 ft. should be maintained along forested shorelines to provide large, tall trees for nesting platforms and cavities, to protect nest trees from blowdowns, and to control erosion and the resulting decrease in water quality. Single-selection cuts may be used within the buffer zone to maintain a closed-canopy forest, with some super-canopy trees remaining, but no clear-cutting should occur (Gerrard et al. 1975, Green 1995).
7) Do not burn, mow, graze, or cut timber during the breeding season (15 April - 15 August).
8) Predation may be a problem in lakes with little surrounding upland habitat. Nest enclosures or predator barriers have been used successfully to reduce mammalian predators in North Dakota (Mayer and Ryan 1991). Additionally, creation of islands on restored wetlands and conversion of peninsulas to islands are also successful in reducing predation (PPJV Shorebird Management Plan, Lokemoen and Messmer 1994).
9) Do not drain wooded wetlands or bottomland forest adjacent to lake habitat (Bellrose and Holm 1994).
10) Protect water quality of lakes to ensure an adequate prey base (Storer and Nuechterlein 1992, Gibbs et al. 1992).
11) Nest boxes may benefit hooded mergansers and other cavity-nesting species, such as the wood duck, along forested shores where standing dead trees are fewer than 1 per acre (Dugger et al. 1994).
General management recommendations in this section pertain to all forest habitat types in the MH/TGP ecosystem. Specific forest habitat types, management recommendations for these habitats, and forest bird species of concern are discussed in order of priority following this section.
Habitat Fragmentation. When deciding which forest patches to conserve or where reforestration might benefit the most species:
1) Avoid fragmentation of existing contiguous forest tracts. Conserving existing forests is easier and more effective than reforestration (Robbins 1988).
2) Consider microhabitats within the forest patch. One reason forest interior species may be absent in small forest patches is that they require a wide range of microhabitats which may be missing in small tracts (Karr 1982). Inclusion of a lake, stream, bog, steep slope, bank, etc. may make smaller habitat patches suitable to a wider range of species (Robinson 1988).
3) Reforest existing artificial forest openings, open peninsulas, and gaps between isolated forest blocks in order to create larger and more valuable forest blocks for area-sensitive species. Reforestration can be achieved through natural succession if funds are limited, but random planting of native trees is more efficient (Herkert et al. 1993).
4) Special care should be taken to assess the benefits of "wildlife openings" for deer and other mammals versus the negative effects to bird species of concern, especially in habitats already heavily fragmented by agriculture, suburban development, or tree harvesting. Small grassy wildlife openings are not beneficial to any High Priority or Priority bird species and may be harmful to many species by creating cowbird feeding opportunities, by increasing predation from both birds and mammals, and by acting as a population sink for grassland species (Green 1995).
5) Consider surrounding habitat. The "effective size" of a 50 ha tract of lowland coniferous forest may be increased if it is surrounded by a larger tract of mature coniferous, or even a mostly deciduous forest, by eliminating the edge effect from the lowland coniferous patch. Mature forests bordered by young forests or a well-developed shrub-sapling habitat may be more beneficial than forests surrounded by agricultural fields.
6) If forest loss cannot be prevented, mitigation plantings should be planned and implemented as far in advance of forest loss as possible and should be designed to enlarge existing forested areas (Herkert et al. 1993).
7) Conservation of small, isolated tracts can also benefit many migratory species. Small forest tracts may be important migratory stop-over sites for forest-interior birds, especially if forest habitat is scarce in the region (Blake 1986).
Timber Management. Timber should not be harvested from wildlife preserves designed to protect bird populations. On public or private land where timber is harvested:
1) Low volume, single-tree selection is the recommended cutting practice, especially in areas already heavily fragmented (Herkert et al. 1993, Robinson and Wilcove 1994, Green 1995). Single-tree selection most closely mimics natural tree falls (Medin and Booth 1989), may benefit gap-dependent species such as the hooded warbler and blue-grey gnatcatcher (Lynch and Whigham 1984, Gartshore 1988), and results in the maintenance of contiguous forest tracts without the fragmentation caused by other types of timber harvest (Green 1995).
2) Avoid clear cuts and large group-selection cuts whenever possible. Group section cuts as small as a quarter of an acre have the potential to increase nest parasitism and predation rates (Robinson et al. 1992). When clear cutting or large group selection cuts are necessary, design cuts to minimize edge.
3) If single-tree selection is not possible, even-age management with a rotation cycle long enough to permit regeneration of large, old trees [80-120 yrs. may be best (Welsh and Healy 1993)] is the next-best option. Rotational cuttings should be planned so that the oldest sections are next to other old sections and the younger stages are adjacent to other young sections. Some tracts should be mature at all stages in the management plan (Herkert et al. 1993, Robinson and Wilcove 1994).
4) Maintenance of permanent core areas will lessen the effects of timber management on forest interior species and can serve as source areas for avian repopulation of younger sections. These mature tracts should be located at the center of the management unit (Herkert et al. 1993).
5) Leaving residual trees (isolated or in clumps) and patches of live vegetation in the harvest site is a better approximation of the natural fire disturbance cycle than traditional clearcuts and will have both immediate and long term positive benefits for shrub and forest species. Residual trees and shrubs provide much needed cavities for roosting and nesting, foraging sites for bark probers and gleaners, hunting perches for raptors, song perches for passerines and boreal owls, and shelter (conifers) for passerines. Residual trees are especially important in the remote forests of northern Minnesota where other types of mitigation are impractical (Niemi and Hanowski 1984, Green 1995).
6) Another forest management system that may minimize the negative effects of logging on forest interior species is selective cuttings in which all dead trees, young trees, and shrubs are left standing and rotational cycles of 25%, 50%, 75%, or 100% of harvestable timber are harvested from selected patches. Although some species respond negativley to any logging, many others showed no effect when this logging regime was used in a northern hardwood forest in New York (Webb et al. 1977).
7) Logging roads should be closed and revegetated soon after harvest to reduce cowbird feeding opportunities (Herkert et al. 1993, Robinson and Wilcove 1994).
8) In accessible areas where mature and standing dead trees are fewer than 1 per acre, nest boxes may be beneficial (Herkert et al. 1993).
7) Reduce disturbances to forest birds by avoiding management/harvesting activities during the nesting season - approximately 1 May - 1 August (Herkert et al. 1993).
Other Management Considerations. The following are general management recommendations that benefit most forest species:
1) Maintain a well developed woody and herbaceous understory in all forested tracts. Promote the redevelopment of a diverse understory in degraded forests by attempting to control over-browsing by white-tailed deer, stopping mowing, and removing livestock (Herkert et al. 1993). Many priority species in the MH/TGP ecosystem depend on the forest understory for food, cover, and nest sites (Table 16).
2) Avoid disturbing forest interior species during the nesting season (approx. 1 May - 1 August) by limiting activities such as picnicking, camping, or hiking to the forest edge (Herkert et al. 1993, Green 1995).
3) Avoid construction projects such as roadways, sewer or power lines, impoundments and other land clearings that increase edge. When construction projects cannot be avoided, avoid construction during the nesting season (Herkert et al. 1993).
4) Although most species are insectivorous during the breeding season (Table 16), berries provide an important migration food. Berry-bearing bushes usually require full sunlight and often occur in wind-fall or harvest gaps. On sites that are intensely managed, these shrubs should be fostered by more judicious use of herbicides and thinning practices that promote them (Green 1995).
Lowland coniferous forest includes semi-open to closed-canopy, coniferous forest, including spruce swamps and bogs. It is the highest priority forest habitat in the MH/TGP ecosystem and ranks fifth among the MH/TGP ecosystem's thirteen primary habitats (Table 4).
Lowland coniferous forest is the primary habitat of eleven bird species including one High Priority species, the Nashville warbler, and one Priority species, the Connecticut warbler (Table 16). These two species have varying habitat requirements, although both are ground nesters and neither is dependent on tall, large trees for nest or foraging sites (Table 1).
Lowland coniferous forest should be managed according to the general forest management recommendations in addition to the following specific suggestions:
1) Although neither lowland coniferous species of concern is dependent on large, tall trees for nest or foraging sites, it is critical to maintain a mature canopy (Green 1995). This will also benefit mature coniferous species of concern in areas where mature, upland coniferous forests are rare (Green 1995).
2) A 200 ft. buffer strip should be maintained on either side of any riparian zone. Single-selection cutting may be used to help maintain a closed canopy forest with well-developed understory, but no clear-cutting should occur within the buffer zone. Some old, supercanopy trees should be preserved for perching and nest sites (Darveau et al. 1995, Green 1995).
3) The effective area of a lowland coniferous forest is increased if surrounded by mature, upland coniferous forest instead of agricultural field or suburban/rural development.
4) Reduce drainage of wooded wetlands and swamps.
5) Harvested stands should be regenerated to conifers. The U.S. Forest Service (1977, p. 5), Mladenoff and Pastor (1993, pp.164-165), and Koter (1994, p. 18) all offer suggestions for promoting the regeneration of conifers through small changes in current forest practices.
Mature deciduous forest (> 30 yrs) ranks sixth in priority of the MH/TGP ecosystem's thirteen primary breeding habitats (Table 4). Thirty species use mature deciduous forest as their primary breeding habitat, including one High Priority species, the cerulean warbler, and nine Priority species (Table 18). Only wetlands (36) and lakes (32) host more species.
Mature deciduous forest has probably suffered more fragmentation than other forest habitats in the MH/TGP ecosystem, and is the most vulnerable to further fragmentation from suburban development, agriculture, and logging pressures. Six of the High Priority and Priority species are highly sensitive to fragmentation, three are moderately sensitive, and only one shows low sensitivity (Table 16). Furthermore, the increased predation and cowbird parasitism that accompanies fragmentation have been cited as major factors in the decline of at least three mature deciduous Priority species (Holmes 1994, Evans Ogden and Stutchbury 1994, Moskoff 1995). The continuing existence of many mature deciduous species in the MH/TGP ecosystem may depend on the preservation of large forest tracts.
Old forests with large, tall trees and well-developed understories are important to most mature, deciduous forest High Priority and Priority species. Eighty percent require a well-developed lower canopy and/or shrub layer and another 80% require a semi-open to closed canopy of large, tall trees. All species require at least one of these characteristics and 60% require both (Table 16). Traditional clear-cut rotations do not allow enough time for forests to develop both of these characteristics sufficiently. Longer harvesting rotations or silvicultural techniques that give the regenerating forest a "jump start," such as leaving clumps of live vegetation and standing live trees, may be necessary to improve forest quality for High Priority and Priority species.
Mature deciduous forest should be managed according to the general forest management recommendations.
Lowland deciduous forest includes semi-open to closed-canopy, bottomland, deciduous forest, and ranks seventh in priority of the MH/TGP ecosystem's thirteen primary habitats (Table 4). Eight species use lowland deciduous forest as their primary breeding habitat including three Priority species, the prothonatory warbler, the Louisiana waterthrush, and the wood duck (Table 19). Specific habitat requirements for these three species vary greatly, although all depend on mature trees for cover, food, and nest sites (Table 16).
In the southern portion of the MH/TGP ecosystem, lowland deciduous forest surrounding rivers or large streams is often the only forest habitat available to birds. Maintaining quality riparian habitat is especially important for rare, riparian-obligate species such as the prothonatory warbler, but it is also critical for migrating birds and upland-forest species, especially in the highly fragmented suburban and agricultural areas of the MH/TGP ecosystem. Conservation on the landscape level may be difficult in these areas, however, because most of the land is privately owned. Educating and encouraging land-owners to form conservation associations so habitat can be managed in large blocks may be the best approach to managing lowland deciduous habitat in the southern portion of the MH/TGP ecosystem. Most riparian zones in the northern forests of the MH/TGP ecosystem are publicly owned and are more easily preserved.
Human activities affect lowland deciduous species in more subtle ways also. Current lock and dam construction, channeling, urban development, and agriculture have greatly altered the floodplain plant community of the upper Mississippi River and other lowland deciduous forests (Moore 1988, Knutson 1995). The present tall, closed-canopy forests could be replaced by forests with smaller trees and more grass and shrub habitats, which would negatively affect many riparian-zone bird species dependent on large, tall trees (Knutson 1995). Techniques need to be developed to restore and maintain forest successional processes that favor a mix of tree species composition, structure, and age.
Lowland deciduous forest should be managed according to the general forest management recommendations along with the following specific recommendations:
1) Riparian species are especially sensitive to the age and composition of forest adjacent to water bodies. Buffer zones of 100-200 ft. should be maintained along shorelines and banks. Single-selection tree cuts may be used to maintain a closed-canopy forest, with some super-canopy trees remaining, but no clear-cutting should occur (Green 1995).
2) Private landowners could plan cooperatively with adjacent landowners to maximize unfragmented areas and to maintain or enhance riparian forests. Consider forming a landowners' association or the development of cooperative management agreements, development restrictions and covenants to protect forest integrity (Herkert et al. 1993).
3) Eliminate stream channelization; restore ditched streams where financially feasible (Bellrose and Holm 1994).
4) Reduce drainage of wooded wetlands and bottomland forests (Bellrose and Holm 1994).
Young deciduous forest includes poletimber-sized, upland, deciduous forest 12-30 years old, and ranks eighth in priority of the MH/TGP ecosystem's thirteen primary habitats (Table 4). Five species use young deciduous forest as their primary breeding habitat including one Priority species, the black-billed cuckoo, three Concern species, the whip-poor-will, rose-breasted grosbeak, and American redstart, and one Low Concern species, the eastern phoebe.
The one Priority species, the black-billed cuckoo, requires a dense, well-developed shrub layer and lower canopy for feeding and nest sites (Table 16). It does not require large areas of contiguous young deciduous habitat, but it is sensitive to habitat isolation and will not inhabit small patches if other suitable habitat is not nearby (Robbins et al. 1989).
In the MH/TGP ecosystem, most young deciduous forest is the result of succession after clearcuts or abandonment of agricultural fields. Young deciduous forest may best be managed by improving habitat quality instead of increasing the total area of habitat available. Habitat quality will be improved by leaving standing residual live trees, all dead trees, and all shrubs and saplings in patches cut for timber (Niemi and Hanowski 1984, Green 1995).
Young deciduous forests should be managed according to general forest management recommendations.
Mature coniferous forest includes upland coniferous forest more than 30 years old, and ranks ninth in priority among the MH/TGP ecosystem's thirteen primary habitats (Table 4). This ranking may not be accurate, however. Mature coniferous forest may rank low in priority because a relatively large proportion of coniferous forest still exists in the MH/TGP ecosystem compared with other habitats, or it may rank low because we have no concern score for 12 (44%) of its 30 species and relatively little information about the habitat requirements, abundance, and population trends of many more of its species. More research must be conducted in mature coniferous forest before we can accurately determine how many of its species are of concern, how it ranks with other habitats, and how to manage it effectively.
Twenty-seven species use mature coniferous forest as their primary breeding habitat, including four Priority species (Table 20). One Priority species, the Canada warbler, is highly sensitive to fragmentation although fragmentation sensitivity of the other three mature coniferous Priority species is unknown. Three Priority species are dependent on large, tall, coniferous trees (>60 yrs), and at least one is dependent on a well-developed understory (Table 16). Food supply may be the limiting resource for one Priority species, the Cape May warbler. This species extends and contracts its range in response to spruce budworm outbreaks, and its productivity and abundance increase dramatically in outbreak years. Thus, population declines in the MH/TGP may signify population shifts rather than overall declines in population and should be further studied (MacArthur 1958).
Mature coniferous forest should be managed according to the general forest management recommendations and the following specific management recommendations:
1) Mature spruce-fir/aspen-birch forests are often succeeded by young aspen-dominated stands when harvested, fragmenting the conifer-dominated landscape. To offset this tendency, harvested stands should be regenerated to conifers or harvests should be designed so large areas of mature conifers remain in the landscape (Green 1995). The U.S. Forest Service (1977, p. 5), Mladenoff and Pastor (1993, pp.164-165), and Koter (1994, p. 18) all offer suggestions for promoting the regeneration of conifers through small changes in current forest practices.
2) Increase length of cutting rotations. Current 50 year cutting rotations do not allow time for conifers to mature sufficiently and decreases habitat suitability for species dependent on tall conifers (Doepker et al. 1992).
3) Do not select only tall trees if single-selection cuttings are used. Selective removal of large conifers decreases the population of blackburnian warblers (Webb et al. 1977), and may decrease populations of other species dependent on tall conifers.
4) Conifer plantations may provide important bird habitat, especially in areas where forest cover has been lost. Manage pine plantations to maintain a greater diversity in species composition and structure. Goals include a more open canopy, natural tree regeneration, and adequate light to support shade-intolerant herbs and shrubs characteristic of natural Jack and red pine stands. Established plantations may achieve this goal by thinning substantial fractions of the canopy at long intervals or by prescribed burning. New plantations may be planted at lower densities with admixtures of other canopy species (Green 1995).
Developed habitat includes urban areas, suburbs, and rural development such as farmsteads and small towns. It ranks tenth in priority of the MH/TGP ecosystem's thirteen habitats (Table 4), and is the primary breeding habitat of one priority species, the peregrine falcon (Table 21). Peregrine falcons were recently reintroduced to the MH/TGP ecosystem after extirpation caused from insecticide poisoning in the 1960s. Reintroduction and management of peregrine falcons have been extensively studied by wildlife managers throughout the Midwest, and will not be discussed in this report.
Agricultural-woodland edge (AgEdge) includes woody fencerows, shelterbelts, orchards, and forest edges in agricultural landscapes, and ranks eleventh in priority of the MH\TGP ecosystem's thirteen primary habitats. None of the twenty species whose breeding habitat is AgEdge are in the High Priority concern class and only one, the loggerhead shrike, is in the Priority concern class (Table 22). Most AgEdge species were originally associated with oak- savannah or they are generalists adapted to a variety of semi-open habitats.
Loggerhead shrikes prefer open habitat such as prairie or pasture with plenty of elevated perches or nest sites within individual territories (Kridelbaugh 1983, Coffin and Pfannmuller 1988, Brooks and Temple 1990a, 1990b, Smith and Cruse 1992). They most frequently nest in trees with a shrubby or bushy growth form such as eastern red cedar, and usually pick isolated trees or trees in hedgerows or windbreaks that are only one tree wide (Brooks and Temple 1990a, Tyler 1992). Nestling growth rate is positively correlated with percent cover of pasture and percent cover of grassland within a 50 m radius (Brooks and Temple 1990a) and abundance is negatively correlated with amount of harvested rowcrops and woodland (Smith and Cruse 1992). Loggerhead shrikes select territories with >50% herbaceous ground cover and over half select territories with >75% herbaceous ground cover (Brooks and Temple 1990a). Male loggerhead shrikes return to the same territory each year (Kridelbaugh 1983, Brooks and Temple 1990a, 1990b).
Three widely discussed reasons for the decline of loggerhead shrikes are 1) loss of breeding habitat, 2) low reproductive success or 3) pesticide poisoning. After discussing the literature and their own data, Brooks and Temple (1990b), rejected all three hypotheses and propose a fourth, that over-winter survival is low. Loggerhead shrike reproductive success is normal, survival on the summer range is good, and much suitable nesting habitat is not occupied, suggesting loggerhead shrikes are below carrying capacity in Minnesota (Brooks and Temple 1990ab). On the other hand, loss of winter habitat in the gulf states and Arkansas is high. Resident shrikes in these states defend winter territories and as habitat decreases, migrating shrikes are pushed onto more and more marginal habitat, most likely affecting their over-winter survival (Brooks and Temple 1990ab).
Whether over-winter survival is the primary cause or one of many factors contributing to the decline of the loggerhead shrike is unknown. Although managers in the MH/TGP ecosystem cannot directly protect shrikes against threats on the wintering grounds, they can help ensure loggerhead shrikes have ample breeding habitat in Minnesota by providing high-quality grassland habitat with nearby tree or shrub cover.
Managing agricultural-woodland edge for loggerhead shrikes need not contradict grassland management plans. The following suggestions address how to provide loggerhead shrike habitat without jeopardizing quality grasslands, the highest priority habitat in the MH/TGP ecosystem.
1) Preserve existing grasslands. High quality grassland is paramount to the nesting success of loggerhead shrikes (Brooks and Temple 1990a).
2) Manage all grasslands according to suggestions given in the grassland section, including removing all trees and shrubs from the central portion of grasslands. Shrub cover and trees should be limited to riparian zones and edges where they can provide loggerhead shrikes nesting and perching opportunities, but negative effects on grassland species are minimized.
3) Although most high priority grassland species need large tracts of quality grassland, loggerhead shrikes do not. Preserving smaller tracts of grassland habitat (<20 acres) could be beneficial to both loggerhead shrikes and grassland species such as the dickcissel that are not sensitive to fragmentation.
4) Preserve existing oak-savannah or pastures that mimic oak-savannah. Isolated pastures with continuous low to moderate grazing pressure do not provide good habitat for grassland birds (Table 9) but have the potential to provide good habitat for shrikes if adequate nesting and perching trees are available in an open pasture (Brooks and Temple 1990a).
5) Preserve existing shelterbelts and consider planting trees one tree wide or in isolated clusters next to farm buildings that are adjacent to pasture, CRP, or prairie. Most grassland birds rarely nest next to tall structures such as buildings. One row of trees or a few isolated trees may not affect nesting grassland birds more than the buildings, but will provide nesting and perching opportunities for shrikes. Shrikes often nest near buildings without any adverse effect on nesting success (Brooks and Temple 1990).
Bank-ledge habitat includes primary succession habitats such as ledges, cliffs, caves, and banks, and ranks twelvth in priority of the MH/TGP ecosystem's thirteen habitats (Table 4). The northern rough-winged swallow, which ranks in the Concern class, and the bank swallow, which ranks in the Low Concern class, are the only species that use bank-ledge as their primary breeding habitat. Cliffs and banks are often important features of lakes or streams for High Priority and Priority species such as the piping plover and the peregrine falcon, however, and should be protected along with adjacent forests or grasslands whenever possible.
Young coniferous includes poletimber-sized, upland, coniferous forest, 12-30 years old, and ranks last in priority of the MH/TGP ecosystem's thirteen primary habitats (Table 4). Only two species use young coniferous forest as their primary breeding habitat, the magnolia warbler, which ranks in the Concern class, and the chipping sparrow, which ranks in the No Concern class. Young coniferous forest's primary value to bird species of concern in the MH/TGP may lie in its potential to age into mature coniferous forest, and it should be managed according to the general forest management recommendations.
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Updated January, 1977.
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