Geology topics

D.J. Twedt

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

At least 37 records · Page 2Linked to original sources

USGS2002

Forest restoration as ecological succession: should we speed it up or slow it down?

Recent assessments of afforestation of agricultural lands in the Mississippi Alluvial Valley imply the importance of quickly developing vertical forest structure to benefit 'wildlife.' We examine this assumption and find that animal species of interest as targets of proactive management, as well as targets of control, occur through the full successional sere. Different species of mammals and birds respond positively to the structure available at different times during succession. Thus, managers must decide on the species and communities they wish to favor. Early successional species, particularly those avian communities occurring during winter, have been heretofore considered only in passing. However, because they occur in areas where herbaceous plants dominate vegetation structure, these communities include species otherwise rare or absent from the landscape. Extensive afforestation in the Mississippi Alluvial Valley provides ephemeral habitat for birds that winter in herbaceous areas. Managers may wish to consider maintaining large tracts in herbaceous vegetation similar to that occurring 3-7 years after cessation of farming activities, as habitat for such birds.

Book chapter↗

USGS2002

Morphometric changes in Yellow-headed Blackbirds during summer in central North Dakota

Temporal stability of morphometric measurements is desirable when using avian morphology as a predictor of geographic origin. Therefore, to assess their temporal stability, we examined changes in morphology of Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) from central North Dakota during summer. Measurements differed among age classes and between sexes. As expected, due to growth and maturation, measurements on hatching-year birds increased over summer. Measurements of adult plumage fluctuated with prebasic molt and exhibited age-specific discontinuities. Body mass of adult birds increased over summer, whereas both culmen length and skull length decreased. Only body length and length of internal skeletal elements were temporally stable in adult Yellow-headed Blackbirds.

Western North American Naturalist↗

USGS2001

Forest area and distribution in the Mississippi alluvial valley: Implications for breeding bird conservation

Knowing the current forest distribution and patch size characteristics is integral to the development of geographically defined, habitat-based conservation objectives for breeding birds. Towards this end, we classified 2.6 million ha of forest cover within the Mississippi Alluvial Valley using 1992 thematic mapper satellite imagery. Although historically this area, from southern Illinois to southern Louisiana, was dominated by forested wetlands, forest cover remains on less than 25% of the floodplain. Remaining forest cover is comprised of > 38,000 discrete forest patches > 2 ha. Mean patch area (64.1±5.2 ha; x̄ ±SE) was highly skewed towards small fragment size. Larger patches had a higher proportion of more hydric forest cover classes than did smaller patches which had a higher proportion of less hydric forest cover classes. Public lands accounted for 16% of remaining forested wetlands. Fewer than 100 forest patches exceeded our hypothesized habitat objective (4000 ha minimum contiguous forest area) intended to support self-sustaining populations of forest breeding birds. To increase the number of forest patches exceeding 4000 ha contiguous area, and thereby increase the likelihood of successful forest bird conservation, we recommend afforestation adjoining existing forest fragments ≥1012 ha and focused within designated Forest Bird Conservation Regions.

Journal of Biogeography↗

USGS2001

Nest survival of forest birds in the Mississippi Alluvial Valley

In the Mississippi Alluvial Valley, flood control has led to a drastic reduction in the area of forest habitat and altered the patchwork of forest cover types. Silvicultural management of the remaining fragmented forests has changed to reflect the altered hydrology of the forests, current economic conditions of the area, and demand for forest products. Because forest type and silvicultural management impact forest birds, differences in avian productivity within these forests directly impact bird conservation. To assist in conservation planning, we evaluated daily nest survival, nest predation rates, and brood parasitism rates of forest birds in relation to different forest cover types and silvicultural management strategies within this floodplain. Within bottomland hardwood forests, nest success of blue-gray gnatcatcher ( Polioptila caerulea , 13%), eastern towhee ( Pipilo erythrophthalmus , 28%), indigo bunting ( Passerina cyanea , 18%), northern cardinal ( Cardinalis cardinalis , 22%), and yellow-billed cuckoo ( Coccyzus americanus , 18%) did not differ from that within intensively managed cottonwood plantations. However, average daily survival of 542 open-cup nests of 19 bird species in bottomland hardwoods (0.9516 ± 0.0028, ∼27% nest success) was greater than that of 543 nests of 18 species in cottonwood plantations (0.9298 ± 0.0035, ∼15% nest success). Differences in daily nest survival rates likely resulted from a combination of differences in the predator community -- particularly fire ants ( Solenopsis invicta ) -- and a marked difference in species composition of birds breeding within these 2 forest types. At least 39% of nests in bottomland hardwood forests and 65% of nests in cottonwood plantations were depredated. Rates of parasitism by brown-headed cowbirds ( Molothrus ater ) were greater in managed cottonwoods (24%) than in bottomland hardwoods (9%). Nest success in planted cottonwood plantations for 18 species combined (∼14%), and for yellow-breasted chat ( Icteria virens , 7%), eastern towhee (14%), indigo bunting (14%), and northern cardinal (17%) did not differ from nest success in cottonwood plantations that were coppiced from root sprouts following pulpwood harvest. Within bottomland hardwood forests, uneven-aged group-selection timber harvest reduced the combined daily nest survival of all species from 0.958 to 0.938, which reduced nest success by about 14%. Specifically, timber harvest reduced nest success of species that nest in the forest midstory and canopy, such as Acadian flycatcher ( Empidonax virescens ), from 32% before harvest to 14% after harvest. Conversely, those species that nest primarily in the shrubby understory-such as northern cardinal-were not affected by timber harvest and maintained an overall nest success of about 33%. Thus, birds nesting in the understory of bottomland hardwood forests are not adversely impacted by selective timber harvest, but there is a short-term reduction in nest success for birds that nest in the canopy and midstory.

Louisiana, Mississippi↗

USGS2001

Artificial cavities enhance breeding bird densities in managed cottonwood forests

The paucity of natural cavities within short-rotation hardwood agroforests restricts occupancy by cavity-nesting birds. However, providing 1.6 artificial nesting cavities (nest boxes)/ha within 3- to 10-year-old managed cottonwood forests in the Mississippi Alluvial Valley increased territory density of cavity-nesting birds. Differences in territory densities between forests with and without nest boxes increased as stands aged. Seven bird species initiated 38 nests in 173 boxes during 1997 and 39 nests in 172 boxes during 1998. Prothonotary warblers (Protonotaria citrea) and eastern bluebirds (Sialia sialis) accounted for 67% of nests; nearly all warbler nests were in 1.8-L, plastic-coated cardboard (paper) boxes, whereas bluebird nests were divided between paper boxes and 3.5-L wooden boxes. Larger-volume (16.5-L) wooden nest boxes were used by eastern screech owls (Otus asio) and great crested flycatchers (Myiarchus crinitus), but this box type often was usurped by honey bees (Apis mellifera). To enhance territory densities of cavity-nesting birds in cottonwood agroforests, we recommend placement of plastic-coated paper nest boxes, at a density of 0.5/ha, after trees are >4 years old but at least 2 years before anticipated timber harvest.

Wildlife Society Bulletin↗

USGS2001

Inability to predict geographic origin of Yellow-headed Blackbirds, Xanthocephalus xanthocephalus, during migration

Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) collected at different breeding locations in Alberta, Saskatchewan, Manitoba, and North Dakota exhibit clearly discernable morphometric differences with larger bodied birds found at more northern and western locations. We reduced eight skeletal measurements and body length from adult female and male Yellow-headed Blackbirds to their first two principal components. Principal component scores progressively increased at more northwestern locations. Principal component scores were also derived from measurements of birds collected in central North Dakota throughout summer and fall. We hypothesized an increase in principal component scores of Yellow-headed Blackbirds from summer through fall within central North Dakota as larger bodied migrants arrived and displaced local breeding birds. However, we were unable to detect an increase in principal component scores from mid-June though mid-September over two years of study. Discriminant models that were developed to distinguish birds breeding in Canada from those breeding in the USA were poor predictors of the migratory status of Yellow-headed Blackbirds. Thus, we were unable to exploit the morphometric differences inherent among Yellow-headed Blackbirds breeding at different geographic locations to quantify the timing or the magnitude of their migration through central North Dakota.

Canadian Field-Naturalist↗

USGS2000

Development of management objectives for breeding birds in the Mississippi Alluvial Valley

We used a six-step process to set habitat objectives and population goals for breeding birds in the Mississippi Alluvial Valley. Specifically, we used existing empirical studies and mathematically derived viable population estimates to define habitat objectives and population goals for bottomland hardwood forest, the most important habitat type in this physiographic area. Although habitat objectives must address both quality and quantity, we concentrate here on the size and number of forest patches in this highly fragmented landscape. To support source populations of all forest breeding birds we recommend the protection/restoration of 52 forest patches that are 4,000-8,000 ha in size, 36 patches of 8,000-40,000 ha, and 13 patches greater than 40,000 ha. Although every physiographic area is unique, the methodology applied here should be applicable in other situations.

Book chapter↗

USGS2000

Development of management objectives for waterfowl and shorebirds within the Mississippi Alluvial Valley

The goal of the Lower Mississippi Valley Joint Venture of the North American Waterfowl Management Plan is to provide sufficient habitat to support 4.3 million wintering ducks and 1.0 million wintering geese annually. Under the assumption that the amount of foraging habitat is the primary limitation to supporting waterfowl population goals in the Mississippi Alluvial Valley (MAV), a habitat objective to make available 285,000 ha of waterfowl foraging habitat is divided among seven states. This habitat objective is further divided between public and private ownership and among three habitat types: Bottomland hardwood forest, moist-soil sites, and agricultural fields. Management objectives for shorebirds within the MAV which provide foraging habitat for 0.5 million shorebirds during their southward migration have been tentatively established. Several as yet unverified assumptions were used in establishing these objectives; consequently, we caution that the objectives are subject to revision as the assumptions are tested. We assumed that 0.5 million shorebirds move through the MAV during late summer and fall, each foraging for an average of 10 days. During this migration period, foraging shorebirds are assumed to require sufficient forage to gain 1 g of biomass per day, in addition to their basal metabolic needs. Given an invertebrate food supply that provides 17.6 kj ? g-1, we calculated that an average 45 g shorebird requires about 8 g of invertebrate forage per day. Further assuming that each ha of managed shorebird habitat can provide 20 kg of invertebrate food resources available to shorebirds, we extrapolated a need for 2000 ha of shorebird foraging habitat. We suggest that the bulk of this foraging habitat be provided on public lands and that it be distributed throughout the MAV.

Book chapter↗

USGS2000

An evaluation strategy for conservation goals of the Mississippi Alluvial Valley

The population goals and habitat objectives established by the Mississippi Alluvial Valley Migratory Bird Initiative are based on several unverified assumptions. We have developed an evaluation strategy that identifies research needed to verify these assumptions. We also have outlined a monitoring strategy designed to track progress toward achieving habitat objectives and population goals.

Book chapter↗

USGS2000

Conservation planning and monitoring avian habitat

Migratory bird conservation plans should not only develop population goals, they also should establish attainable objectives for optimizing avian habitats. Meeting population goals is of paramount importance, but progress toward established habitat objectives can generally be monitored more easily than can progress toward population goals. Additionally, local or regional habitat objectives can be attained regardless of perturbations to avian populations that occur outside the geographic area covered by conservation plans. Assessments of current avian habitats, obtained from remotely sensed data, and the historical distribution of habitats should be used in establishing habitat objectives. Habitat planning and monitoring are best conducted using a geographic information system. Habitat objectives are assigned to three categories: maintaining existing habitat, restoring habitat, and creating new or alternative habitat. Progress toward meeting habitat objectives can be monitored through geographic information systems by incorporating georeferenced information on public lands, private lands under conservation easements, corporate lands under prescribed management, habitat restoration areas, and private lands under alternative management to enhance wildlife values. We recommend that the area and distribution of habitats within the area covered by conservation plans be reassessed from remotely sensed imagery at intervals appropriate to detect predicted habitat changes.

Book chapter↗

USGS2000

Comparison of line transects and point counts for monitoring spring migration in forested wetlands

We compared the efficacy of 400-m line transects and sets of three point counts at detecting avian richness and abundance in bottomland hardwood forests and intensively managed cottonwood (Populus deltoides) plantations within the Mississippi Alluvial Valley. We detected more species and more individuals on line transects than on three point counts during 218 paired surveys conducted between 24 March and 3 June, 1996 and 1997. Line transects also yielded more birds per unit of time, even though point counts yielded higher estimates of relative bird density. In structurally more-complex bottomland hardwood forests, we detected more species and individuals on line transects, but in more-open cottonwood plantations, transects surpassed point counts only at detecting species within 50 m of the observer. Species richness and total abundance of Nearctic-Neotropical migrants and temperate migrants were greater on line transects within bottomland hardwood forests. Within cottonwood plantations, however, only species richness of Nearctic-Neotropical migrants and total abundance of temperate migrants were greater on line transects. Because we compared survey techniques using the same observer, within the same forest stand on a given day, we assumed that the technique yielding greater estimates of avian species richness and total abundance per unit of effort is superior. Thus, for monitoring migration within hardwood forests of the Mississippi Alluvial Valley, we recommend using line transects instead of point counts.

Journal of Field Ornithology↗

USGS1999

Impact of forest type and management strategy on avian densities in the Mississippi Alluvial Valley, USA

Avian territory densities were determined from 20 Breeding Bird Censuses in mature (>30 years) bottomland hardwood stand: and 18 Breeding Bird Censuses in young (6-9 years old) cottonwood (Populas deltoides) plantations in the Mississippi Alluvial Valley. Avian species richness, diversity, and territory density were greater (p < 0.01) in bottomland hardwood stands than in intensively-managed cottonwood stands but these parameters were not impacted by selective timber harvest within bottomland hardwood stands nor by method of regeneration within cottonwood plantations (p > 0.05). Even so, detrended correspondence analysis based on avian territory densities readily segregated forest types and silvicultural treatments. Timber harvest within bottomland hardwood stands resulted in a shift in bird communities toward those found in cottonwood stands by increasing the densities of early-successional species such as Indigo Bunting (Passerina cyanea), Yellow-breasted Chat (Icteria virens), and Common Yellowthroat (Geothlypis trichas). Conversely, regenerating cottonwood stands from root sprouts, rather than planting stem cuttings, resulted in a shift in bird communities toward those found in bottomland hardwood stands by increasing densities of species such as White-eyed Vireo (Vireo griseus) and Wood Thrush (Hylocichla mustelina). Tree species diversity, angular canopy cover, and midstory density were positively associated with bird species assemblages in bottomland hardwood stands, whereas vegetation density at ground level was positively associated with bird communities in cottonwood plantations. Conversion of agricultural fields to short-rotation cottonwood plantations results in increased breeding bird populations by adding up to 140 additional territories 40 ha-1. Even so, relative conservation values, derive, from indicator species analysis and Partners in Flight concern scores, suggest that mature bottomland hardwood forests are twice as 'valuable' for bird conservation as are cottonwood plantations.

Forest Ecology and Management↗

USGS1999

Temporal differences in point counts of bottomland forest landbirds

We compared number of avian species and individuals in morning and evening point counts during the breeding season and during winter in a bottomland hardwood forest in west-central Mississippi. USA. In both seasons, more species and individuals were recorded during morning counts than during evening counts. We also compared morning and evening detections for 18 species during the breeding season and 9 species during winter. Blue Jay (Cyanocitta cristata), Mourning Dove (Zenaida macroura), and Red-bellied Woodpecker (Melanerpes carolinus) were detected significantly more often in morning counts than in evening counts during the breeding season. Tufted Titmouse (Baeolophus bicolor) was recorded more often in morning Counts than evening counts during the breeding season and during winter. No species was detected more often in evening counts. Thus, evening point counts of birds during either the breeding season or winter will likely underestimate species richness, overall avian abundance, and the abundance of some individual species in bottomland hardwood forests.

The Wilson Bulletin↗

USGS1999

Waterfowl density on agricultural fields managed to retain water in winter

Managed water on private and public land provides habitat for wintering waterfowl in the Mississippi Valley, where flood control projects have reduced the area of natural flooding. We compared waterfowl densities on rice, soybean, and moist-soil fields under cooperative agreements to retain water from 1 November through 28 February in Arkansas and Mississippi and assessed temporal changes in waterfowl density during winter in 1991-1992 and 1992-1993. Fields flooded earlier in Arkansas, but retained water later in Mississippi. Over winter, waterfowl densities decreased in Arkansas and increased in Mississippi. Densities of waterfowl, including mallard (Anas platyrhynchos), the most abundant species observed, were greatest on moist-soil fields. However, soybean fields had the greatest densities of northern shoveler (Spatula clypeata).

Wildlife Society Bulletin↗

USGS1998

Increasing point-count duration increases standard error

We examined data from point counts of varying duration in bottomland forests of west Tennessee and the Mississippi Alluvial Valley to determine if counting interval influenced sampling efficiency. Estimates of standard error increased as point count duration increased both for cumulative number of individuals and species in both locations. Although point counts appear to yield data with standard errors proportional to means, a square root transformation of the data may stabilize the variance. Using long (>10 min) point counts may reduce sample size and increase sampling error, both of which diminish statistical power and thereby the ability to detect meaningful changes in avian populations.

Journal of Field Ornithology↗

USGS1997

Evaluation of a mallard HSI model for the Lower Mississippi Valley

We evaluated a habitat suitability (HSI) model developed for mallards ( Anas platyrhynchos ) wintering in the Lower Mississippi Valley by comparing mallard densities obtained from aerial surveys with habitat suitability indices derived from satellite imagery for 25, 256km 2 sampling units. Regression models that related mallard densities to habitat suitability indices accounted for only 29% of the variability in the data and the 95% confidence interval of predicted mallard densities included zero for most habitat suitability indices evaluated. Thus, we conclude that the published HSI model is a poor predictor of wintering mallard density in the Lower Mississippi Valley. We suggest model revision to allow users to remotely obtain model inputs for habitat characteristics at landscape scales. Further, we suggest the model be revised to consider yearly variation in habitat and flood conditions that better reflect the ability of an area to support wintering mallards.

Arkansas, Louisiana, Mississippi↗

USGS1996

A land manager's guide to point counts of birds in the Southeast

Current widespread concern for the status of neotropical migratory birds has sparked interest in techniques for inventorying and monitoring populations of these and other birds in southeastern forest habitats. The present guide gives detailed instructions for conducting point counts of birds. It further presents a detailed methodology for the design and conduct of inventorial and monitoring surveys based on point counts, including discussion of sample size determination, distribution of counts among habitats, cooperation among neighboring land managers, vegetation sampling, standard data format, and other topics. Appendices provide additional information, making this guide a stand-alone text for managers interested in developing inventories of bird populations on their lands.

General Technical Report↗

USGS1996

Seed deterioration in flooded agricultural fields during winter

We determined rate of seed deterioration for 3 crops (corn, rice, and soybean) and 8 weeds commonly found in agricultural fields and moist-soil management units in the Mississippi Alluvial Valley (MAV). The weeds were broadleaf signalgrass (Brachiaria platyphylla), junglerice barnyardgrass (Echinochloa colonum), morningglory (Ipomoea sp.), panic grass (Panicum sp.), bull paspalum (Paspalum boscianum), red rice (Oryza sativa), hemp sesbania (Sesbania exaltata), and bristlegrass (Setaria sp.). Weed seeds, except morningglory, deteriorated slower than corn and soybean, whereas rice decomposed slower than all weed seeds except red rice and bull paspalum. For land managers desiring to provide plant food for wintering waterfowl, rice is clearly the most persistent small grain crop in the MAV. Persistence of weed seeds under flooded conditions throughout winter makes them a cost-effective alternative to traditional crops on land managed for waterfowl.

Wildlife Society Bulletin↗