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D.J. Twedt

Publications and source records attributed to D.J. Twedt.

At least 19 recordsLinked to original sources
USGS2008

Bird response to silviculture induced change in forest structure within bottomland hardwood forests

Silvicultural treatments prescribed to encourage development of desired stand structure (i.e., wildlife-forestry) should result in increased abundance of many bird species of management concern, especially species using dense understory habitat. Desired forest conditions within bottomland vary among sites, but average 60-70% overstory canopy that is heterogeneously distributed with >5 dominant trees/ha retained, and a basal area of 14-16 m2/ha. Desired mid-story and understory cover are between 25-40%. Cavity trees (small and large) as well as dead and/or stressed trees should be retained, ultimately providing >14 m3/ha coarse woody debris, and shade-intolerant tree regeneration should be present on 30-40% of the area. We assessed avian response to prescribed wildlife-forestry silviculture treatments via distance-adjusted point counts and constant effort mist-netting within forest stands on Tensas River National Wildlife Refuge in northeastern Louisiana. More species and individuals were detected within stands 1-13 years post-treatment than within untreated stands. Most species, especially species benefiting from disturbance, increased in density after treatment. A few species decreased in density, yet remained fairly relatively abundant post-treatment. Captures from netting suggested three generalized responses to wildlife-forestry silviculture: (1) species with rapid, short-duration positive response, (2) species with slower but more prolonged positive response, and (3) species which initially declined but had long-term positive population response. We recommend increased use of prescribed wildlife-forestry silvicultural prescriptions to enhance bottomland forest habitat for priority bird species.

Book chapter↗
USGS2008

Winter bird population studies and project prairie birds for surveying grassland birds

We compared 2 survey methods for assessing winter bird communities in temperate grasslands: Winter Bird Population Study surveys are area-searches that have long been used in a variety of habitats whereas Project Prairie Bird surveys employ active-flushing techniques on strip-transects and are intended for use in grasslands. We used both methods to survey birds on 14 herbaceous reforested sites and 9 coastal pine savannas during winter and compared resultant estimates of species richness and relative abundance. These techniques did not yield similar estimates of avian populations. We found Winter Bird Population Studies consistently produced higher estimates of species richness, whereas Project Prairie Birds produced higher estimates of avian abundance for some species. When it is important to identify all species within the winter bird community, Winter Bird Population Studies should be the survey method of choice. If estimates of the abundance of relatively secretive grassland bird species are desired, the use of Project Prairie Birds protocols is warranted. However, we suggest that both survey techniques, as currently employed, are deficient and recommend distance- based survey methods that provide species-specific estimates of detection probabilities be incorporated into these survey methods.

Southeastern Naturalist↗
USGS2006

Direct seeding woody species for restoration of bottomlands

I direct seeded (broadcast) seeds of 39 species of trees and shrubs using an ATV-mounted rotary spreader to initiate restoration of bottomland forest on retired agricultural sites. Four sites were planted during February, 2000, and 13 additional sites were planted during April and May, 2001. After two growing seasons, stem density of direct-seeded species varied greatly among study plots (range = 0 to 888 stems/ha) but averaged only 110 stems/ha. I recommend that future efforts at direct seeding focus on seven shrub species (Amorpha fruticosa L., Cephalanthus occidentalis L., Cornus spp., Crataegus spp., Ilex decidua Walt., Morus rubra L., and Prunus spp.) and seven tree species (Celtis laevigata Willd., Diospyros virginiana L., Fraxinus spp., Gleditsia triacanthos L., Robinia pseudoacacia L., Taxodium distichum (L.) Rich, and Ulmus spp.) that successfully established in these trials.

Book chapter↗
USGS2006

Risky business: Site selection by Acadian Flycatchers under threat of nest predation and brood parasitism

Habitat quality is determined not only by habitat structure and the availability of resources, but also by competitors, cooperators, predators, and parasites. We hypothesized that, for passerines, minimizing risk from avian nest predators and brood parasites is an important factor in selecting a breeding site. Through the early part of two breeding seasons, we spot-mapped locations of Acadian Flycatchers (Empidonax virescens, territory selectors), Red-bellied Woodpeckers (Melanerpes carolinus, nest predators) and Brown-headed Cowbirds (Molothrus ater, brood parasites) in a 56-ha study area within an extensive bottomland hardwood forest. We were thereby able to determine the order of flycatcher territory settlement and nest initiation in relation to risk of predation and parasitism, while accounting for habitat structure. Male settlement was influenced by both habitat structure and risk avoidance. However, risk trom woodpeckers was relatively more important in the first season and risk from cowbirds in the second, evidently due to differences in the relative abundance of predator and brood-parasite in each year. For male flycatchers, settlement choices appear to be flexible in the face of changing 'risk landscapes.' For females, habitat structure was the most important predictor of nest site selection. Even so, there was evidence that females avoided cowbirds. Surprisingly, nest site selection was positively associated with woodpecker abundance in the first season when woodpeckers were present in greater numbers. Possible explanations for this contradictory result are discussed.

Book chapter↗
USGS2006

A spatially explicit decision support model for restoration of forest bird habitat

The historical area of bottomland hardwood forest in the Mississippi Alluvial Valley has been reduced by >75%. Agricultural production was the primary motivator for deforestation; hence, clearing deliberately targeted higher and drier sites. Remaining forests are highly fragmented and hydrologically altered, with larger forest fragments subject to greater inundation, which has negatively affected many forest bird populations. We developed a spatially explicit decision support model, based on a Partners in Flight plan for forest bird conservation, that prioritizes forest restoration to reduce forest fragmentation and increase the area of forest core (interior forest >1 km from 'hostile' edge). Our primary objective was to increase the number of forest patches that harbor >2000 ha of forest core, but we also sought to increase the number and area of forest cores >5000 ha. Concurrently, we targeted restoration within local (320 km2) landscapes to achieve >60% forest cover. Finally, we emphasized restoration of higher-elevation bottomland hardwood forests in areas where restoration would not increase forest fragmentation. Reforestation of 10% of restorable land in the Mississippi Alluvial Valley (approximately 880,000 ha) targeted at priorities established by this decision support model resulted in approximately 824,000 ha of new forest core. This is more than 32 times the amount of core forest added through reforestation of randomly located fields (approximately 25,000 ha). The total area of forest core (1.6 million ha) that resulted from targeted restoration exceeded habitat objectives identified in the Partners in Flight Bird Conservation Plan and approached the area of forest core present in the 1950s.

Conservation Biology↗
USGS2006

Small clusters of fast-growing trees enhance forest structure on restored bottomland sites

Despite the diversity of trees in bottomland forests, restoration on bottomland sites is often initiated by planting only a few species of slow-growing, hard mast?producing trees. Although successful at establishing trees, these young forests are slow to develop vertical structure, which is a key predictor of forest bird colonization. Furthermore, when natural seed sources are few, restored sites may be depauperate in woody species. To increase richness of woody species, maximum tree height, and total stem density, I supplemented traditional plantings on each of 40 bottomland restoration sites by planting 96 Eastern cottonwood (Populus deltoides) and American sycamore (Platanus occidentalis) in eight clusters of 12 trees. First year survival of cottonwood stem cuttings (25%) and sycamore seedlings (47%) was poor, but survival increased when afforded protection from competition with weeds. After five growing seasons, 165 of these 320 supplemental tree clusters had at least one surviving tree. Vegetation surrounding surviving clusters of supplemental trees harbored a greater number of woody species, increased stem density, and greater maximum tree height than was found on paired restoration sites without supplemental trees. These increases were primarily accounted for by the supplemental trees.

Restoration Ecology↗
USGS2006

Combining Breeding Bird Survey and distance sampling to estimate density of migrant and breeding birds

We combined Breeding Bird Survey point count protocol and distance sampling to survey spring migrant and breeding birds in Vicksburg National Military Park on 33 days between March and June of 2003 and 2004. For 26 of 106 detected species, we used program DISTANCE to estimate detection probabilities and densities from 660 3-min point counts in which detections were recorded within four distance annuli. For most species, estimates of detection probability, and thereby density estimates, were improved through incorporation of the proportion of forest cover at point count locations as a covariate. Our results suggest Breeding Bird Surveys would benefit from the use of distance sampling and a quantitative characterization of habitat at point count locations. During spring migration, we estimated that the most common migrant species accounted for a population of 5000-9000 birds in Vicksburg National Military Park (636 ha). Species with average populations of 300 individuals during migration were: Blue-gray Gnatcatcher (Polioptila caerulea), Cedar Waxwing (Bombycilla cedrorum), White-eyed Vireo (Vireo griseus), Indigo Bunting (Passerina cyanea), and Ruby-crowned Kinglet (Regulus calendula). Of 56 species that bred in Vicksburg National Military Park, we estimated that the most common 18 species accounted for 8150 individuals. The six most abundant breeding species, Blue-gray Gnatcatcher, White-eyed Vireo, Summer Tanager (Piranga rubra), Northern Cardinal (Cardinalis cardinalis), Carolina Wren (Thryothorus ludovicianus), and Brown-headed Cowbird (Molothrus ater), accounted for 5800 individuals.

Condor↗
USGS2005

Landscape level reforestation priorities for forest breeding landbirds in the Mississippi Alluvial Valley

Thousands of ha of cleared wetlands are being reforested annually in the Mississippi Alluvial Valley (MAV). Despite the expansive and long-term impacts of reforestation on the biological communities of the MAV, there is generally a lack of landscape level planning in its implementation. To address this deficiency we used raster-based digital data to assess the value of forest restoration to migratory landbirds for each ha within the MAV. Raster themes were developed that reflected distance from 3 existing forest cover parameters: (1) extant forest, (2) contiguous forest patches between 1,012 and 40,000 ha, and (3) forest cores with contiguous area <5,200 ha. Forest core habitat was any forest habitat >1 km from an agricultural, urban, or pastoral edge. Two additional raster themes were developed that combined information on the proportion of forest cover and average size of forest patches, respectively, within landscapes of 50,000, 100,000, 150,000, and 200,000 ha. Data from these 5 themes were amalgamated into a single raster using a weighting system that gave increased emphasis to existing forest cores, larger forest patches, and moderately forested landscapes while deemphasizing reforestation near small or isolated forest fragments and within largely agricultural landscapes. This amalgamated raster was then modified by the geographic location of historical forest cover and the current extent of public land ownership to assign a reforestation priority score to each ha in the MAV. However, because reforestation is not required on areas with extant forest cover and because restoration is unlikely on areas of open water and urban communities, these lands were not assigned a reforestation priority score. These spatially explicit reforestation priority scores were used to simulate reforestation of 368,000 ha (5%) of the highest priority lands in the MAV. Targeting restoration to these high priority areas resulted in a 54% increase in forest core - an area of forest core that exceeded the area of simulated reforestation. Bird Conservation Regions, developed within the framework of the Partners in Flight: Mississippi Alluvial Valley Bird Conservation Plan, encompassed a large proportion (circa 70%) of the area with highest priority for reforestation. Similarly, lands with high reforestation priority often were enrolled in the Wetland Reserve Program.

Book chapter↗
USGS2005

Bottomland hardwood establishment and avian colonization of reforested sites in the Mississippi Alluvial Valley

Reforestation of bottomland hardwood sites in the Mississippi Alluvial Valley has markedly increased in recent years, primarily due to financial incentive programs such as the Wetland Reserve Program, Partners for Wildlife Program, and state and private conservation programs. An avian conservation plan for the Mississippi Alluvial Valley proposes returning a substantial area of cropland to forested wetlands. Understanding how birds colonize reforested sites is important to assess the effectiveness of avian conservation. We evaluated establishment of woody species and assessed bird colonization on 89 reforested sites. These reforested sites were primarily planted with heavy-seeded oaks (Quercus spp.) and pecans (Carya illinoensis). Natural invasion of light-seeded species was expected to diversify these forests for wildlife and sustainable timber harvest. Planted tree species averaged 397 + 36 stems/ha-1, whereas naturally invading trees averaged 1675 + 241 stems/ha. However, naturally invading trees were shorter than planted trees and most natural invasion occurred <100 m from an existing forested edge. Even so, planted trees were relatively slow to develop vertical structure, especially when compared with tree species planted and managed for pulpwood production. Slow development of vertical structure resulted in grassland bird species, particularly dickcissel (Spiza americana) and red-winged blackbird (Agelaius phoeniceus), being the dominant avian colonizers for the first 7 years post-planting. High priority bird species (as defined by Partners in Flight), such as prothonotary warbler (Protonotaria citrea) and wood thrush (Hylocichla mustelina), were not frequently detected until stands were 15 years old. Canonical correspondence analysis revealed tree height had the greatest influence on the bird communities colonizing reforested sites. Because colonization by forest birds is dependent on tree height, we recommend inclusion of at least one fast-growing tree species (e.g., cottonwood [Populus deltoides], or sycamore [Platanus occidentalis]) in the planting stock to encourage rapid avian colonization.

Book chapter↗
USGS2005

Bottomland hardwood restoration in the Mississippi Alluvial Valley: Looking past the trees to see the forest

Planned restoration of bottomland hardwoods is important to adequately address negative consequences resulting from the severe loss and fragmentation of forested wetlands in the Mississippi Alluvial Valley. Reforestation efforts have been promoted through government initiatives of state and federal agencies (e.g. Wetland Reserve Program) and private conservation groups. To clarify discussions of forested wetland restoration, we offer definitions of reforestation and restoration, review historic reforestation practices, identify additional needs, and propose a conceptual framework to assist in future reforestation efforts. Future reforestation efforts should include: (1) comprehensive planning among participating agencies, (2) standardized documentation of methods, and (3) short-term and long-term monitoring protocols that permit refinement of methodologies. Implementation of these concepts will promote cooperative planning among participants and facilitate research to evaluate bottomland hardwood restoration efforts.

Book chapter↗
USGS2005

Waiting for trees to grow: nest survival, brood parasitism, and the impact of reforestation efforts

Of the forested wetlands that once covered the Mississippi Alluvial Valley, only -25% remain due to large-scale conversion to agriculture. Reforestation efforts are currently underway, but tracts planted with slow-growing oaks maintain the structure of a grassland for 5 yr or longer, and will require at least 40 yr to resemble a mature forest. Nonetheless, it is hoped that reforestation, even in early stages, can effectively increase core area in extant tracts of mature forest by reducing higher rates of nest failure and brood parasitism often associated with forest-agriculture interfaces. To test this, we monitored nests of a mature-forest specialist, the Acadian Flycatcher, in extensive bottomland forests adjacent to agricultural fields and reforested tracts (<20 yr-old). We used an information-theoretic approach to evaluate alternative hypotheses regarding the relative impacts of agriculture and reforestation in the landscape. Controlling for year, season, and stand basal area, there was little evidence that landscape context significantly affected nest survival, although survival tended to increase with decreasing amounts of agriculture. The probability of brood parasitism increased with greater proportions of open habitats in the landscape. There was much stronger support for the hypothesis that parasitism rates depended on the sum of agricultural and reforested tracts, rather than on the amount of agriculture alone. Thus, reforested tracts are not expected to have the desired effect of reducing parasitism rates in the adjacent mature forest until several decades have passed.

Book chapter↗
USGS2005

An objective method to determine an area's relative significance for avian conservation

Land managers are often concerned with providing habitat affords the 'best habitat for songbirds.' However, unless management simply is directed at rare species it may not be clear which habitats or management options are best. A standard, quantifiable measure to compare the significance of different tracts of land or competing management techniques for avian conservation would benefit managers in decision making. I propose a standard measure that is based on the relative density of each species within a finite area and their respective regional Partners in Flight concern scores. I applied this method to > 100 reforested sites in the Mississippi Alluvial Valley that ranged in age from 2 to 32 years. The objectively determined avian conservation significance for each of these reforested sites was correlated with stand age and with my subjective assessment of 'habitat quality.' I also used this method to compare the avian conservation significance of forested habitats before and after selective timber harvest with high significance for avian conservation provided habitat for species of conservation concern. I recommend application of this methodology to other and areas under different management, to determine its usefulness at predicting avian conservation significance among habitats and at various avian densities.

Book chapter↗
USGS2005

Winter status of White-eyed Vireos in northeastern Louisiana

In December 2004, February 2005, and June 2005, we recaptured a White-eyed Vireo (Vireo griseus) that was banded on 19 May 2004 at the same location on the Tensas River National Wildlife Refuge, Madison Parish, LA. This is the first documented permanent resident White-eyed Vireo outside of resident populations known from Florida and southern Texas. This individual appears to be resident near the northern limit of the winter range for the species. Although White-eyed Vireos are uncommon in northeastern Louisiana during winter, we detected other White-eyed Vireos during line transect surveys and banding during winters 2003-2004 and 2004-2005. The lack of research and observation of winter birds in northern Louisiana and the secretive and inconspicuous behavior of White-eyed Vireos in winter may have led to an underestimation of abundance at the northern limits of their winter range.

North American Bird Bander↗
USGS2004

Stand development on reforested bottomlands in the Mississippi Alluvial Valley

Reforestation of bottomland hardwood sites in the southeastern United States has markedly increased in recent years due, in part, to financial incentives provided by conservation programs. Currently >250,000 ha of marginal farmland have been returned to hardwood forests. I observed establishment of trees and shrubs on 205 reforested bottomlands: 133 sites were planted primarily with oak species ( Quercus spp . ), 60 sites were planted with pulpwood producing species ( Populus deltoides , Liquidambar styraciflua , or Platanus occidentalis ), and 12 sites were not planted (i.e., passive regeneration). Although oak sites were planted with more species, sites planted with pulpwood species were more rapidly colonized by additional species. The density of naturally colonizing species exceeded that of planted species but density of invaders decreased rapidly with distance from forest edge. Trees were shorter in height on sites planted with oaks than on sites planted with pulpwood species but within a site, planted trees attained greater heights than did colonizing species. Thus, planted trees dominated the canopy of reforested sites as they matured. Planted species acted in concert with natural invasion to influence the current condition of woody vegetation on reforested sites. Cluster analysis of species importance values distinguished three woody vegetation conditions: (1) Populus deltoides stands (2) oak stands with little natural invasion by other tree species, and (3) stands dominated by planted or naturally invading species other than oaks. Increased diversity on reforested sites would likely result from (a) greater diversity of planted species, particularly when sites are far from existing forest edges and (b) thinning of planted trees as they attain closed canopies.

Arkansas, Kentucky, Louisiana, Mississippi, Missou↗
USGS2004

Sex Determination of Carolina Wrens (Thryothorus ludovicianus) in the Mississippi Alluvial Valley

I identified sexual dimorphism in wing length (unflattened chord) of Carolina Wrens (Thryothorus ludovicianus) within the central Mississippi Alluvial Valley (northeast Louisiana and west-central Mississippi) and used this difference to assign a sex to captured wrens. Wrens were identified as female when wing length was less than 57.5 mm or male when wing length was greater than 58.5 mm. Verification of predicted sex was obtained from recaptures of banded individuals where sex was ascertained from the presence of a cloacal protuberance or brood patch. Correct prediction of sex was 81% for adult females and 95% for adult males. An alternative model, which categorized wrens with wing lengths of 58 and 59 mm as birds of unknown sex, increased correct prediction of females to 93% but reduced the number of individuals to which sex was assigned. These simple, predictive, wing-length-based models also correctly assigned sex for more than 88% of young (hatching-year) birds.

North American Bird Bander↗