Partners in Flight
Bird Conservation Plan
for the
Mississippi
Alluvial Valley
(Physiographic Area # 05)
Version 1.0
September 1999
Written by: Daniel Twedt, David Pashley, Chuck Hunter, Allen Mueller, Cindy Brown, and Bob Ford
Address comments to:
Bob Ford, c/o U.S. Fish and Wildlife Service, University of Memphis, South Campus, Bldg 8, Memphis, TN 38152
901-327-1752; fax 901-327-8001; bford@tnc.org
Partners in Flight Bird Conservation Plans are living documents that are periodically updated and improved as knowledge of bird management and conservation in the physiographic area is improved. Thus the first public draft of this Bird Conservation Plan is Version 1.0. This Plan will remain a work in progress, we encourage those who wish to contribute to do so.
The following individuals participated in drafting or revision of this conservation plan: S. Ray Aycock, Charles K. Baxter, Cindy Brown, Robert J. Cooper, Lisa Creasman, Tom Foti, Robert P. Ford, Paul B. Hamel, Bob Hatcher, Doug Helmers, W. C. (Chuck) Hunter, Brad Jacobs, Sunni Lawless, Charles R. Loesch, Curt McMurl, Seth E. Moth, Allen J. Mueller, Gary Myers, David N. Pashley, Lance Peacock, Terry Rich, Karen Rowe, Janet Ruth, Jon Schneider, Mike Staten, Mark Swan, Daniel J. Twedt, William B. Uihlein, Bill Vermillion, Mark S. Woodrey, and Scott C. Yaich.
§ TABLE OF CONTENTS
o Forested wetlands, bottomland hardwood forests
o Forest Openings, Edges, Early-Successional Shrub-Scrub
o Upland Oak-Hickory Hardwoods
o Grasslands/Savannas, Pastures, and Associated Wetlands.
o Lacustrine (open-water) Wetlands, Palustrine (emergent) Wetlands, and Mudflats.
- SECTION 4: IMPLEMENTATION RECOMMENDATIONS AND SUMMARY.
- LITERATURE CITED
- Table 1. Native habitats and current land use of physiographic provinces within the Mississippi Alluvial Valley.
- Table 2. Hydrologic units within the Mississippi Alluvial Valley.
- Table 3. Priority bird species.
- Table 4. Hypothesized forest area (hectares) required to support viable populations of 500 breeding birds within the Mississippi Alluvial Valley.
- Table 5. Area of bottomland hardwood forest types.
- Table 6. Habitat objectives for predominately mature, forested wetlands.
- Table 7. Area in hectares of forested habitat within the Mississippi Alluvial Valley.
- Table 8. Area of shrub/scrub and grassland habitats (in hectares) within the Mississippi Alluvial Valley.
- Table 9. Area of upland forest (in hectares) on ridges within the Mississippi Alluvial Valley.
- Table 10. Twenty-five years (1966-1991) of Breeding Bird Survey population trends.
- Table 11. Shorebird species, average mass, and hypothesized abundance during southward migration through the Mississippi Alluvial Valley.
- Table 12. Proposed distribution of managed foraging habitat for shorebirds.
- Figure 1. Mississippi Alluvial Valley physiographic province.
- Figure 2. Bottomland hardwood forest habitat patch objectives.
- Figure 3. Proposed balance sheet to be used to track progress toward shorebird foraging-habitat objectives
- Appendix 1. Tree species
- Appendix 2. Breeding bird species priorities, percent of population (PP), area's importance (AI), population trend (PT), and typical habitat
- Appendix 3. Methodology used to establish foraging habitat objectives for shorebirds
- Appendix 4. Qualitative Characterization of Bird Conservation Areas in the Mississippi Alluvial Valley
- Appendix 5. Quantitative Characterization of Bird Conservation Areas (BCA)in the Mississippi Alluvial Valley
The Mississippi Alluvial Valley (Fig. 1) is an 11 million ha (24 million acres), relatively flat, weakly dissected alluvial plain, comprised of natural levees, basins and flats, point bar formations, terraces, tributary floodplains, and depressional wetlands. Differences in topography and hydrology result in 14 physiographic provinces spanning 7 states (Table 1; Keys et al. 1995). Elevation ranges from 0 to 200 m (0-660 feet) with local relief generally <30 m but reaching up to 100 m along ridges and bluffs bordering the mainstem Mississippi River. Because elevation differences are slight, hydrologic regimes can dramatically influence vegetation. In addition to 21 internal hydrologic units (Table 2), the Mississippi Alluvial Valley receives drainage from many eastern and central U.S. watersheds, including the Ohio, Arkansas, and Red Rivers. Average annual precipitation is 114 to 165 cm (45-65 in).
Potential natural vegetation for most of the physiographic area is southern
floodplain forest with oak-hickory forest on higher ground (e.g.,
Crowley's Ridge, loess bluffs) and isolated native prairies (e.g., Grand
Prairie). Floodplain forests are primarily oak-gum-cypress cover type with
co-dominant species being overcup, willow, Nuttall, water, swamp chestnut, and
cherrybark oaks, as well as sweetgum, water tupelo, water hickory, willow,
cottonwood, sycamore, hackberry, sugarberry, red maple, boxelder, baldcypress,
and green ash (scientific names of trees listed in Appendix
1). Oak-hickory forests
include as co-dominants post, southern red, black, and white oaks, and
shellbark, shagbark, and mockernut hickories. Remnant prairies have bluestem (Andropogon
spp.) and switchgrass (Panicum virgatum) as the dominant grasses under
natural conditions. Natural vegetation has been cleared from 80% of this
physiographic area primarily for conversion to agriculture. Pasture and
haylands are common on higher ground and along levees. Cotton, soybean, and
rice are the most widespread crops but winter wheat, corn, sorghum, and sugar
cane can be locally abundant. Although cleared of natural vegetation, flooded
agricultural fields can provide important wildlife habitat.
Flood regimes that have historically dictated vegetative communities within the Mississippi Alluvial Valley have been altered by an extensive system of levees, dikes, and dams. High water events have been reduced in many areas, whereas the rate and extent of flooding has been increased in other areas. The altered hydrology of the Mississippi Alluvial Valley has in turn influenced the composition and structure of forested wetlands as well as the amount of open water-shoreline habitat. Local perturbations include ice-storms, tornadoes, hurricanes, beaver ponds, and fire. The northern portion of the Mississippi Alluvial Valley overlays the New Madrid fault line with the potential for earthquakes.
|
Table 1. Native habitats and current land use of physiographic provinces within the Mississippi Alluvial Valley. |
|
|||
|
State |
Physiographic Province |
Native Habitats |
Land Use |
|
|
Arkansas |
Southern Mississippi River Alluvial Plain |
cottonwood - willow, oak - sweetgum, tupelo - cypress |
cropland, forestry |
|
|
Crowley's Ridge |
post - blackjack oak, southern red oak - white oak, beech - maple |
pasture |
||
|
Arkansas Grand Prairie |
willow oak - overcup oak, bluestem - switchgrass |
agriculture |
||
|
Arkansas Alluvial Plain |
overcup oak - sweetgum, green ash - American elm-hackberry - sugarberry |
agriculture |
||
|
Macon Ridge |
southern red oak - white oak - post oak - hickory [pignut, mockernut, sand] |
agriculture, forestry |
||
|
Bastrop Ridge |
southern red oak - white oak - post oak - hickory [pignut, mockernut, sand], shortleaf pine - oak [white, southern red, post, black] |
agriculture, forestry |
||
|
North Mississippi River Alluvial Valley |
river birch - sycamore, overcup oak - sweetgum |
agriculture |
||
|
White and Black Rivers Alluvial Plain |
oak - sweetgum, overcup oak - water hickory, tupelo - cypress |
cropland |
||
|
St. Francis River Alluvial Plain |
overcup oak - sweetgum, green ash - American elm - hackberry - sugarberry |
agriculture |
|
|
|
Illinois |
North Mississippi River Alluvial Valley |
river birch - sycamore, overcup oak - sweetgum |
agriculture |
|
|
Kentucky |
North Mississippi River Alluvial Valley |
river birch - sycamore, overcup oak - sweetgum |
agriculture |
|
|
Louisiana |
Southern Mississippi River Alluvial Plain |
cottonwood - willow, oak - sweetgum, tupelo - cypress |
agriculture, forestry |
|
|
Baton Rouge Terrace |
loblolly pine - oak [cherrybark, swamp chestnut, Shumard], shortleaf pine - oak [white, southern red, post, black] |
agriculture |
||
|
Atchafalaya Alluvial Plain |
water tupelo - bald cypress, overcup oak - sweetgum |
agriculture |
||
|
Macon Ridge |
southern red oak - white oak- post oak - hickory [pignut, mockernut, sand] |
agriculture, forestry |
||
|
Red River Alluvial Plain |
oak [swamp chestnut, cherrybark, Shumard] - sweetgum, green ash - American elm - hackberry - sugarberry |
agriculture |
||
|
Bastrop Ridge |
southern red oak - white oak - post oak - hickory [pignut, mockernut, sand], shortleaf pine - oak [white, southern red, post, black] |
agriculture, forestry |
||
|
Opelousa Ridge |
loblolly pine - oak [cherrybark, swamp chestnut, Shumard], oak - sweetgum |
agriculture, forestry |
||
|
Teche Terrace |
oak [swamp chestnut, cherrybark, Shumard] - sweetgum, green ash - American elm - hackberry - sugarberry |
agriculture |
|
|
|
Mississippi |
Southern Mississippi River Alluvial Plain |
cottonwood - willow, oak - sweetgum, tupelo - cypress |
agriculture |
|
|
North Mississippi River Alluvial Valley |
river birch - sycamore, overcup oak - sweetgum |
agriculture |
|
|
|
Missouri |
Crowley's Ridge |
post - blackjack oak, southern red oak - white oak, beech - maple |
agriculture, forestry |
|
|
North Mississippi River Alluvial Valley |
river birch - sycamore, overcup oak - sweetgum |
agriculture |
||
|
White and Black Rivers Alluvial Plain |
oak - sweetgum, overcup oak - water hickory, tupelo - cypress |
agriculture |
||
|
St. Francis River Alluvial Plain |
overcup oak - sweetgum, green ash - American elm - hackberry - sugarberry |
agriculture |
|
|
|
Tennessee |
North Mississippi River Alluvial Valley |
river birch - sycamore, overcup oak - sweetgum |
agriculture |
|
Conservation issues:
The Mississippi Alluvial Valley is among the most heavily modified physiographic areas in the southeastern U.S. but still supports the largest forested floodplain in North America. In addition to providing forested habitat for breeding birds, the area serves as a major waterfowl wintering area, supplying food and cover from both forested and agricultural habitats. Resident and migrant long-legged wading birds as well as transient shorebirds exploit natural floodwater, flooded farm fields, and aquaculture ponds.
Although habitats for waterbirds have not historically been a focus for Partners in Flight, we address habitat needs of nongame waterbirds because bird conservation between landbirds and waterbirds overlap extensively within the Mississippi Alluvial Valley. Nevertheless, waterbird goals, objectives, and priorities fall under the purview of other bird conservation groups such as the Western Hemispheric Shorebird Reserve Network, the Colonial Waterbird Society, and North American Waterfowl Management Plan Committee. The objectives outlined here will be integrated with objectives established by other conservation groups (e.g., Lower Mississippi Valley Joint Venture Evaluation Plan [Loesch et al. 1994]).
Forestry in the southeastern U.S. has a long history, with the present forested acreage referred to as the "South's Fourth Forest" (USDA Forest Service 1988, Walker 1991). Virtually no virgin timber remains and, even with increasing region-wide forest acreage, there have been dramatic changes in forest types dominating the landscape. Indeed, a number of "old-growth" forest species are now extinct, endangered, or vulnerable. Some avian species dependent upon forested habitats are extinct (e.g., passenger pigeon [Ectopistes migratorius], Carolina parakeet [Conuropsis carolinensis]) and other species are endangered and likely extinct (e.g., Ivory-billed Woodpecker, Bachman's Warbler). Non-avian species, such as the red wolf (Canis rufus) and the Louisiana black bear (Ursus americanus luteolus) have also suffered from loss of forested wetland habitat.
The Mississippi Alluvial Valley has the dubious distinction of being the most deforested of all southeastern physiographic areas. Forest fragmentation usually refers to a landscape where a still large percentage of forest remains but is fragmented into small blocks surrounded by non-forested habitat (usually agriculture or suburban/urban development). The Mississippi Alluvial Valley, however, is now largely non-forested with >80% of the land in agricultural production. Remaining forest patches are generally surrounded by vast expanses of farmland. Continuing debates on the decline of forest birds in other parts of eastern North America, where the percent of the landscape in forest remains high, have been resolved in the Mississippi Alluvial Valley. Forests, and the birds dependent upon them, have greatly declined throughout this century, with losses continuing since the 1950's (about 360,000 ha [900,000 acres] lost between the mid-1970's and mid-1980's; Hefner et al. 1995). Nevertheless, the remaining forests, of all types, provide valuable wildlife habitat.
|
Table 2. Hydrologic units within the Mississippi Alluvial Valley. |
|
|
State |
Hydrologic Unit |
|
Arkansas |
Black / Middle White, Cache / Lower White, St. Francis / L'Anguille, Lower Arkansas / Bayou Meto, Ouachita, Boeuf / Bayou Bartholomew |
|
Illinois |
Cache |
|
Kentucky |
West Kentucky |
|
Louisiana |
Boeuf / Ouachita, Tensas / Bayou Macon, Red River Backwater, Teche / Vermilion, Atchafalaya, Barataria / Terrebonne |
|
Mississippi |
Steele Bayou, Big Sunflower, Tallahatchie, Lower Yazoo, Southwest Mississippi |
|
Missouri |
Bootheel |
|
Tennessee |
West Tennessee |
Conservation opportunities:
The greatest opportunity for bird conservation in the Mississippi Alluvial Valley is the existence of the Lower Mississippi Valley Joint Venture (LMVJV) of the North American Waterfowl Management Plan (NAWMP). This effort was originally devoted to betterment of conditions for waterfowl, but this infers improvement of wetland habitat and improved health of wetland ecosystems. Given that the vast majority of the MAV consists of wetlands, efforts to benefit waterfowl populations and those for forest-breeding non-game birds are often compatible or even identical in nature. Due in part to this overlap, the LMVJV has worked closely with Partners in Flight and others to develop a cohesive effort to conserve all birds within the system. The strength and success of PIF in this physiographic area is in large part due to this close partnership with the Joint Venture.
At the heart of the biological foundation of bird conservation in the MAV is adherence to roles and relationships among planning, implementation, and evaluation. The Joint Venture and its many partners have a long history of implementation during which numerous properties have been acquired by public agencies and managed for waterfowl, other game species, and/or as functional bottomland hardwood systems. Much of the currently forested land in the Valley is either on a National Wildlife Refuge, state Wildlife Management Area, National Forest, or other public property. In recent years, planning and evaluation have become much more significant components of the conservation process in the MAV, and this Bird Conservation Plan is one manifestation of this shift.
One important tool developed for planning and evaluation has been a Geographic Information System (GIS) that is now centered in the Joint Venture office in Vicksburg, MS, with significant support from The Nature Conservancy of Louisiana and other partners. This GIS has been used to characterize and map all forested habitat in the physiographic area, which has been an essential tool in development of forest patch objectives for forest-breeding birds. Public lands and other important features have also been digitized, and current work is dedicated toward mapping of flood events of various intensities in an effort to locate lands most amenable to restoration.
Another key wildlife conservation planning process in the MAV is underway for the Louisiana black bear, which is listed as federally threatened and the focus of activity of the Black Bear Conservation Committee. Like Partners in Flight, the Black Bear Conservation Committee includes representation from public agencies, private landowners, non-governmental conservation organizations, and academia; it has particularly strong representation from the forest products industry. The goal of the Black Bear Conservation Committee is to restore healthy bear populations in the Alluvial Valley and beyond. A single healthy population requires approximately 100,000 acres of bottomland hardwood forest, under some variety of management regimes. This is comparable, both in size and habitat conditions, to the larger blocks developed as forest bird objectives. The Black Bear Conservation Committee will probably recommend that five or so blocks of this size be restored or maintained between the latitude of the lower stretches of the Arkansas and White Rivers and the Gulf of Mexico. This is entirely compatible with Partners in Flight recommendations, and the combined efforts of the two groups should make this shared goal more achievable.
Management of forests for timber production is in most ways compatible with the conservation of high priority birds. Patch cuts are a widely employed silvicultural options that, within a largely forested landscape, are consistent with the habitat needs of species such as kites that forage over open areas, as well as with those of species such as the Swainson's Warbler that favor a mosaic of forest understory. Special attention to forest openings is necessary to minimize parasitism and predation even in the larger forest patches. For example, it may be advisable to maintain no more than 10-15% of an area in right-of-ways, other permanent openings, regeneration cuts, or other temporary openings at any given time. Edges within the "interior" of forests should be gradual rather than abrupt (Suarez et al. 1997). Additionally, retention of scattered patches of tall, >25 m, trees (e.g., baldcypress and cottonwood) in existing forests will provide potential nest site locations.
As another example, uneven age silviculture appears to be compatible with habitat requirements of Cerulean Warblers. However, if timber volume targets are high (e.g. >40% of the canopy removed) this type of uneven-aged management may result in excessive fragmentation. In these cases, larger regeneration cuts (e.g., 8-16 ha) combined with longer rotations (e.g., 150-200 years) and thinning to ensure maximum tree girth may still result on maintenance of large mature hardwood stands over time. Only monitoring, coupled with adaptive management, can confirm which silvicultural practices are beneficial to high priority bird species.
The importance of private lands for conservation of avian populations in the Mississippi Alluvial Valley must not be underestimated. Education of and support by private landowners is critical in that most future reforestation efforts are likely to occur on private lands. Opportunities to improve habitat conditions for avian species must consider the management objectives of private landowners. Many of the opportunities to work with private landowners to restore and manage forested wetlands through a variety private lands assistance programs are summarized in Coreil et al. 1997 and can be seen at http://www.agctr.lsu.edu/wwwac. As an example of the success of incentive programs on private lands, implementation of the USDA's Wetland Reserve Program has resulted in reforestation of over 100,000 ha of cleared land.
Probably because so much original forest has been removed from the MAV, the forest that remains is highly valued by local residents, both for hunting and aesthetic reasons. Unlike previous decades in which conversion from forest to agricultural use increased land value, most sites that are currently forested lose value when cleared. This is partially because most remaining forested sites are wetter areas least favorable to agriculture, but also because of the value of land on which hunting for deer, waterfowl, turkey, and other small game is an option. Most non-industrial private forested land is now either owned by hunting clubs or is leased for hunting to generate income. Hunting clubs are now often able to bid more for forested land than are farmers intent on conversion. Land in the ownership of limited partnership hunting clubs is extremely unlikely to be cleared for other uses anytime in the near future. The benefits of this condition to non-game forest birds are great, in that bird conservation objectives are being met on private lands, voluntarily by the landowners, at no acquisition or incentives cost to public agencies.
Long term bird conservation in the Mississippi Alluvial Valley can best be sustained through implementation of detailed planning, communication, and working partnerships among an array of government agencies, private conservation organizations, landowners, and citizens. This process will lead to an understanding of this region's natural history, foster regional pride, and instills the conservation ethic necessary to sustain and restore the diverse biotic communities of this ecosystem. Various groups exist that can merge federal, state, and private interests to coordinate management actions and resolve potential conflicts. For instance, much of the current conservation planning effort underway in the Mississippi Alluvial Valley was outlined through the efforts of the Lower Mississippi Valley Joint Venture sanctioned under the North American Waterfowl Management Plan. However, much work needs to be done to better coordinate management needs with the private sector. Landowner incentives, conservation easements, and market development can all be used to increase private participation in conservation efforts.
Within the Mississippi Alluvial Valley, data on land cover (U.S. Geological Survey, Twedt 1996) and ownership (U.S. Fish and Wildlife Service, The Nature Conservancy), forest seral stages, and trends (U.S. Forest Service [www.srsfia.usfs.msstate.edu] are available for assessment of avian habitat. State Working Groups of Partners in Flight can use these data, and the recommendation herein, to assess their public and private land opportunities, thereby defining local roles and responsibilities for achieving the population goals and habitat objectives outlined below.
At least 107 bird species nest regularly in the Mississippi Alluvial Valley, excluding wading birds and colonial nesting waterbirds (Appendix 2). Most of these species occur in more than one broad habitat type as defined within this plan. Forest breeding species remain the most important component of the avifauna, despite the loss of nearly 80% of the forested wetlands in this region. At least 70 species occur in bottomland hardwoods as a primary habitat. Greater than 20% of the breeding populations of Swainson's Warbler, Prothonotary Warbler, and Swallow-tailed Kite are found within the Mississippi Alluvial Valley. Typical species of bottomland hardwood forests include Northern Parula Warbler, Swainson's Warbler, Prothonotary Warbler, Red-shouldered Hawk, and Red-headed Woodpecker.
At least 62 species occur in upland oak-hickory forests, although many of these species occur in bottomland hardwoods as well. Typical species include Yellow-billed Cuckoo, Worm-eating Warbler, Black-and-white Warbler, and Broad-winged Hawk. At least 25 species occur in scrub-shrub habitats in the Mississippi Alluvial Valley. Typical species include Painted Bunting, Orchard Oriole, White-eyed Vireo, Common Yellowthroat, and Indigo Bunting.
At least 18 species occur in Mississippi Alluvial Valley grassland habitats. Typical species include Dickcissel, Loggerhead Shrike, Field Sparrow, Northern Bobwhite, and Grasshopper Sparrow. Seven species are dependent on water and wetlands habitat, including Hooded Merganser, Wood Duck, Belted Kingfisher, and Marsh Wren. Another 19 species occur in a variety of other habitats, such as open water or river banks. These species include Purple Martin, Tree Swallow, and Barn Owl.
The Partners in Flight prioritization process was developed to guide conservation actions among diverse birds and habitats (see Hunter et al. 1993, Carter et al. in press). The system ranks each species based on 7 measures of conservation vulnerability: relative abundance, size of breeding and non-breeding ranges, threats during breeding and non-breeding seasons, population trend, and relative density. In addition, the percentage of a species global breeding population that occurs in a physiographic area has been provided (Rosenberg and Wells, pers. comm.). To further refine species prioritization within a physiographic area, population trends and area importance are examined independently of total scores.
Birds were prioritized according to this scheme in the Mississippi Alluvial Valley (Table 3). Category I lists highest priority birds and included 14 species which received a Partners in Flight score of 22 or more. Two species were excluded from the prioritization process in the Mississippi Alluvial Valley, Bachman's Warbler and Ivory-billed Woodpecker are most likely extinct. Other species of highest priority are Swainson's Warbler, Prothonotary Warbler, Cerulean Warbler, and Swallow-tailed Kite. The remainder of Category I birds occur mostly in bottomland hardwood forests, although birds of upland forests and scrub-shrub habitats are represented.
Category II provides a list of slightly lower priority species, and included another 9 species with slightly lower total scores (19 to 21), but combined with a high score for area importance and population trend. These species reflected mostly scrub-shrub habitats. Four species are included in Category III. These birds received high global concern scores as Watchlist species (Cater et al. in press), regardless of their status in the Mississippi Alluvial Valley.
Category IV birds have a high combination of scores for area importance and population trend, regardless of total score. In the Mississippi Alluvial Valley, 4 species occur in this category. Nine species are in Category V; each species has greater than 5% of their national breeding status within the Mississippi Alluvial Valley. Species with greater than 10% of their breeding population, that have not been listed elsewhere in this table, include Barred Owl and
Mississippi Kite. Categories VI and VII list federally threatened and endangered species, as well as species of state concern. Combined, these categories include 7 species.
|
Table 3. Priority bird species listed by
total PIF concern score, and segregated by entry criteria. Other measures
include are of importance and population trends scores, percent of BBS
populations, and local migratory status. [Refer to Appendix 2 for scientific names] |
||||||||
|
Priority and species |
Total PIF score |
Concern scores A1 PT |
Percent BBS |
Local migratory status |
||||
|
Ia. Highest overall priority |
||||||||
|
Swainson's Warbler |
29 |
5 |
3 |
20.8 |
B |
|||
|
Swallow-tailed Kite |
28 |
4 |
3 |
25.1 |
E |
|||
|
Cerulean Warbler |
28 |
3 |
4 |
- |
E |
|||
|
Ib. High overall priority |
||||||||
|
Prothonotary Warbler |
24 |
5 |
2 |
34.8 |
B |
|||
|
Painted Bunting |
24 |
3 |
5 |
4.4 |
B |
|||
|
Red-headed Woodpecker |
23 |
5 |
5 |
3.0 |
D |
|||
|
Bell's Vireo |
23 |
2 |
3 |
1.0 |
B |
|||
|
Northern Parula |
23 |
5 |
5 |
6.9 |
B |
|||
|
Worm-eating Warbler |
23 |
2 |
3 |
- |
B |
|||
|
Kentucky Warbler |
22 |
3 |
3 |
4.7 |
B |
|||
|
Orchard Oriole |
22 |
5 |
5 |
7.4 |
B |
|||
|
Yellow-billed Cuckoo |
22 |
5 |
5 |
6.0 |
B |
|||
|
Wood Thrush |
22 |
3 |
3 |
1.3 |
B |
|||
|
White-eyed Vireo |
22 |
4 |
5 |
8.4 |
B |
|||
|
II. Physiographic area priority species |
||||||||
|
Yellow-breasted Chat |
21 |
5 |
5 |
6.2 |
B |
|||
|
Northern Bobwhite |
20 |
3 |
5 |
- |
R |
|||
|
Eastern Wood-Pewee |
20 |
3 |
5 |
- |
B |
|||
|
Carolina Chickadee |
20 |
4 |
5 |
- |
R |
|||
|
Loggerhead Shrike |
20 |
4 |
4 |
- |
R |
|||
|
Field Sparrow |
20 |
3 |
5 |
- |
D |
|||
|
Baltimore Oriole |
20 |
3 |
5 |
- |
B |
|||
|
Ruby-throated Hummingbird |
19 |
5 |
3 |
7.3 |
B |
|||
|
Blue-gray Gnatcatcher |
19 |
4 |
5 |
- |
B |
|||
|
III. Additional species: global priority |
||||||||
|
Scissor-tailed Flycatcher |
21 |
3 |
3 |
- |
B |
|||
|
Dickcissel |
21 |
4 |
2 |
5.1 |
B |
|||
|
Chuck-will's-widow |
21 |
4 |
3 |
3.1 |
B |
|||
|
Prairie Warbler |
20 |
2 |
3 |
- |
B |
|||
|
IV. Additional species: abundant and declining in physiographic area |
||||||||
|
Indigo Bunting |
17 |
4 |
5 |
- |
B |
|||
|
Common Grackle |
16 |
5 |
5 |
- |
D |
|||
|
Mourning Dove |
14 |
4 |
5 |
- |
D |
|||
|
Northern Mockingbird |
14 |
4 |
5 |
- |
D |
|||
|
V. Additional species: responsibility for monitoring (>5% BBS population estimate) |
||||||||
|
Mississippi Kite |
21 |
4 |
2 |
13.4 |
B |
|||
|
Acadian Flycatcher |
20 |
3 |
2 |
5.6 |
B |
|||
|
Carolina Wren |
18 |
5 |
3 |
6.5 |
R |
|||
|
Red-bellied Woodpecker |
18 |
5 |
2 |
6.1 |
R |
|||
|
Red-shouldered Hawk |
17 |
4 |
2 |
9.8 |
D |
|||
|
Purple Martin |
17 |
5 |
2 |
7.8 |
B |
|||
|
Barred Owl |
16 |
5 |
2 |
15.6 |
R |
|||
|
Northern Cardinal |
16 |
5 |
2 |
5.7 |
R |
|||
|
Black Vulture |
12 |
3 |
3 |
8.3 |
D |
|||
|
VI. Federal listed species |
||||||||
|
Bald Eagle |
18 |
3 |
3 |
- |
D |
|||
|
VII. Local, state, or regional interest species |
||||||||
|
Hooded Warbler |
21 |
3 |
3 |
- |
|
|||
|
Yellow-throated Warbler |
20 |
3 |
2 |
- |
|
|||
|
American Redstart |
20 |
3 |
3 |
- |
|
|||
|
Yellow-throated Vireo |
20 |
3 |
2 |
- |
|
|||
|
Summer Tanager |
18 |
2 |
3 |
- |
|
|||
|
Pileated Woodpecker |
16 |
4 |
2 |
- |
|
|||
Conservation area size considerations
Other than the above issues of site characteristics, the basic consideration regarding habitat is that the current landscape of the MAV is 80% deforested, most remaining forested patches are small and isolated (Twedt and Loesch, in press), and there is no reason to presume that the vast majority of this system will ever again be forested. Objectives for bird populations in forested habitat, therefore, are related to size, configuration, number (and to some extent distribution and inter-connectivity) of individual habitat patches. The quantity of habitat required can conceptually be separated into
issues of 1) patch size and context; and 2) number and distribution of patches (populations). Size and configuration will be addressed in this section whereas the issue of number of patches and their distribution will be addressed thereafter.
Forest patches should be of sufficient size to support source populations of targeted bird species, to minimize the likelihood of extirpation, and to ensure a low probability of genetic degradation. The issues that must be resolved in order to select an appropriately-sized patch of habitat for breeding birds are: 1) context, or how ought breeding birds be buffered from the negative influence of surrounding matrices; 2) desired number of breeding pairs to constitute a source population with a high probability of long-term viability; and 3) the density at which birds tend to occur within habitat likely to be included in average patches. Area can be conceptually calculated using the formula:
A = (N * D) + B,
where A = Area of forest required to support a source population (ha),
N = Desired number of breeding pairs
D = Density of breeding birds (expressed as area / breeding pair), and
B = The area (ha) of a 1-km-wide forested buffer around the core forest area (N * D).
The agricultural matrix in which forest patches in the MAV are embedded is generally considered hostile to forest breeding birds in that many MAV land uses support Brown-headed Cowbirds and a wide range of nest predators. We assume that the edges of forest blocks are more seriously affected by brood parasitism and nest predation than are areas farther into the interior of blocks, although the relationship between negative effects distance from edge has not been rigorously tested in the MAV. However, there are data that indicate that the distance between breeding and feeding locations for Brown-headed Cowbirds averages 1.2 km (Thompson 1994). For planning purposes, therefore, we have assumed that the negative impacts on a core surrounded by a 1 km forest buffer will be reduced. Furthermore, for at least some species, birds breeding in forest interiors are more likely to be paired with a mate than are birds breeding near forest edges (Van Horn et al. 1995). Only those pairs within the forest core, therefore, are assumed to reproduce at a rate sufficient to serve as a source population. Clearly, the assumptions in this logical process need to be tested.
The area occupied by a 1-km-wide buffer will vary with the geometric configuration of forest patches. For planning purposes, until the actual area of interior forest within each forest patch is determined, doubling the core forest area (i.e., 2 *[N * D]) will generally result in a total area that includes a 1-km-wide buffer around the desired interior forest area. This assumption holds for more compact small forest patches. For example, a relatively compact 4,000 ha forest patch would be expected to have 2,000 ha of forest interior inside its 1-km-wide forest buffer. This interior area is assumed capable of harboring 500 breeding pairs of all bottomland forest species that occur at densities of <4 ha per breeding pair (i.e., 500 pairs * 4 ha/pair = 2000 ha). The ratio of land required to maintain a 1 km wide buffer to interior core area increases as block configuration becomes less compact.
Minimum viable population and source populations