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At least 649 records · Page 36Linked to original sources
USGS2009

A nonlethal microsampling technique to monitor the effects of mercury on wild bird eggs

Methylmercury is the predominant chemical form of mercury reported in the eggs of wild birds, and the embryo is the most sensitive life stage to methylmercury toxicity. Protective guidelines have been based mainly on captive-breeding studies with chickens (Gallus gallus), mallards (Anas platyrhynchos), and ring-necked pheasants (Phasianus colchicus) or on field studies where whole eggs were collected and analyzed and the effects of the mercury were measured based on the reproductive success of the remaining eggs. However, both of these methods have limitations. As an alternative, we developed a technique that involves extracting a small sample of albumen from a live egg, sealing the egg, returning the egg to its nest to be naturally incubated by the parents, and then relating the hatching success of this microsampled egg to its mercury concentration. After first developing this technique in the laboratory using chicken and mallard eggs, we selected the laughing gull (Larus atricilla) and black-necked stilt (Himantopus mexicanus) as test subjects in the field. We found that 92% of the microsampled laughing gull eggs met our reproductive endpoint of survival to the beginning of hatching compared to 100% for the paired control eggs within the same nests. Microsampled black-necked stilt eggs exhibited 100% hatching success compared to 93% for the paired control eggs. Our results indicate that microsampling is an effective tool for nonlethally sampling mercury concentrations in eggs and, as such, can be used for monitoring sensitive species, as well as for improving studies that examine the effects of mercury on avian reproduction.

Environmental Toxicology and Chemistry↗
USGS1955

Salt-water encroachment as induced by sea-level excavation on Angaur Island

Angaur, southwesternmost of the Palau Islands, 800 miles southwest of Guam, has an area of 3.2 square miles and consists of reef limestone of Pliocene through Recent age. In the northwestern part of the island a basin is formed by a ringlike ridge that has a maximum altitude of 150 feet. To the east and south a series of arc-shaped lower ridges and intervening depressions are concentric with the ring ridge. Beyond these, a low plain with shallow swales composes the remaining two-thirds of the island. The ridges are composed of indurated limestone, whereas the plain is underlain chiefly by unconsolidated coralline fragments. Phosphate has been mined from the three types of topographic depressions since 1908. When power equipment was introduced, excavations were extended below sea level. Lakes formed in these excavations and, despite an annual rainfall of 110 inches, contamination of fresh-water supplies and of agricultural land by salt water resulted from tidal pulsations through the fissured rock. As a result, stoppage of mining was imminent unless remedial measures could be devised. Angaur provides a model of the operations of a Ghyben-Herzberg fresh-water lens on an oceanic island. At numerous lakes, wells, and test holes, continuing observations were made on water levels; amplitude and lag of tidal fluctuations; and mineral content, pH, and temperature of the lens. These observations guided the selection of constantly adjusted remedial measures, which included partitioning of lakes, and bottom filling or back filling of compartments that failed to freshen because of fissures connecting them with the sea. © 1955 Society of Economic Geologists, Inc.

Angaur↗
USGS1975

Fluid inclusion studies of vein, pipe, and replacement deposits, northwestern San Juan Mountains, Colorado

Base and precious metal ores valued in excess of $300 million have been mined from vein, pipe, and replacement deposits located on the northwest side of, and structurally related to, the middle Tertiary Silverton caldera. A belt of normal faults radial to the caldera contains veins which have been mined for as much as 15,000 feet (4,600 m) along strike and 3,700 feet (1,100 m) downdip. Structural relations, metal distributions, and fluid inclusion data suggest that many of the veins were open at the same general time and received the same mineralization. Fluid inclusions in quartz and sphalerite of the main ore stage of the Argentine and adjoining veins have filling temperatures ranging from 315 degrees to 249 degrees C and salinities from 7.9 to 0.1 wt percent NaCl equivalent. However, the majority of inclusions from base metal and gold stages are in a relatively narrow range near 280 degrees to 290 degrees C and salinities are unusually low (less than 2 wt %). Filling temperatures in postsulfide quartz and fluorite are as low as 153 degrees C and salinities are generally less than 0.5 wt percent. A pressure correction of about +25 degrees C should be added to the filling temperatures. Ore fluids were physically homogeneous liquids over the 3,700-foot (1,100 m) vertical and 11,200-foot (3,400 m) lateral range studied and no systematic variations in filling temperatures or salinity in this space are noted, but significant fluctuations are evident locally. Recently developed base metal replacement deposits occur in the Eocene Telluride Conglomerate adjacent to many metal-bearing veins. Calc-silicate alteration of the conglomerate host was probably by moderately saline fluids that ranged in temperature from 320 degrees to about 400 degrees C. Quartz-bearing clasts in altered zones contain secondary halitebearing inclusions with filling temperatures of about 250 degrees C and salinities about 34 wt percent; such inclusions are not known from the base metal stage and are interpreted to have been preore. Hydrothermal quartz, sphalerite, and calcite from replacement pods contain inclusions with filling temperatures ranging from 204 degrees to 309 degrees C and salinities from 11.2 to 0.2 wt percent. That the replacement zones and throughgoing veins are genetically related is suggested by the similarity of filling temperatures and compositions of base metal-stage fluid inclusions and by structural evidence. Small high-grade pipe deposits of base and precious metals occur along the ring-fault zone of the Silverton caldera. Filling temperatures for inclusions in quartz, sphalerite, and barite of the main ore stage of these deposits range from 216 degrees to 308 degrees C and salinities range from 1.6 to 0.2 wt percent NaCl. Quartz in altered wall rocks and silicified capping contains moderately saline secondary inclusions with relatively uniform liquid: vapor ratios that suggest filling temperatures of about 225 degrees to 300 degrees C. From the available samples there is no fluid inclusion evidence for boiling. Throttling, which had been hypothesized to explain the telescoped nature of the pipe ores, is neither substantiated nor discredited by the inclusion data.

Colorado↗
USGS1982

Acid rain, air pollution, and tree growth in southeastern New York

Whether dendroecological analyses could be used to detect changes in the relationship of tree growth to climate that might have resulted from chronic exposure to components of the acid rain-air pollution complex was determined. Tree-ring indices of white pine ( Pinus strobus L.), eastern hemlock ( Tsuga canadensis (L.) Cart.), pitch pine ( Pinus rigida Mill.), and chestnut oak ( Quercus prinus L.) were regressed against orthogonally transformed values of temperature and precipitation in order to derive a response-function relationship. Results of the regression analyses for three time periods, 1901–1920, 1926–1945, and 1954–1973 suggest that the relationship of tree growth to climate has been altered. Statistical tests of the temperature and precipitation data suggest that this change was nonclimatic. Temporally, the shift in growth response appears to correspond with the suspected increase in acid rain and air pollution in the Shawangunk Mountain area of southeastern New York in the early 1950's. This change could be the result of physiological stress induced by components of the acid rain-air pollution complex, causing climatic conditions to be more limiting to tree growth.

New York↗
USGS2000

Nitrite fixation by humic substances: Nitrogen-15 nuclear magnetic resonance evidence for potential intermediates in chemodenitrification

Studies have suggested that NO − 2 , produced during nitrification and denitrification, can become incorporated into soil organic matter and, in one of the processes associated with chemodenitrification, react with organic matter to form trace N gases, including N 2 O. To gain an understanding of the nitrosation chemistry on a molecular level, soil and aquatic humic substances were reacted with 15 N-labeled NaNO 2 , and analyzed by liquid phase 15 N and 13 C nuclear magnetic resonance (NMR). The International Humic Substances Society (IHSS) Pahokee peat and peat humic acid were also reacted with Na 15 NO 2 and analyzed by solid-state 15 N NMR. In Suwannee River, Armadale, and Laurentian fulvic acids, phenolic rings and activated methylene groups underwent nitrosation to form nitrosophenols (quinone monoximes) and ketoximes, respectively. The oximes underwent Beckmann rearrangements to 2° amides, and Beckmann fragmentations to nitriles. The nitriles in turn underwent hydrolysis to 1° amides. Peaks tentatively identified as imine, indophenol, or azoxybenzene nitrogens were clearly present in spectra of samples nitrosated at pH 6 but diminished at pH 3. The 15 N NMR spectrum of the peat humic acid exhibited peaks corresponding with N-nitroso groups in addition to nitrosophenols, ketoximes, and secondary Beckmann reaction products. Formation of N-nitroso groups was more significant in the whole peat compared with the peat humic acid. Carbon-13 NMR analyses also indicated the occurrence of nitrosative demethoxylation in peat and soil humic acids. Reaction of 15 N-NH 3 fixated fulvic acid with unlabeled NO − 2 resulted in nitrosative deamination of aminohydroquinone N, suggesting a previously unrecognized pathway for production of N 2 gas in soils fertilized with NH 3

Soil Science Society of America Journal↗
USGS2009

Hydrologic characterization of desert soils with varying degrees of pedogenesis: 1. field experiments evaluating plant-relevant soil water behavior

To assess the eff ect of pedogenesis on the soil moisture dynamics infl uencing the character and quality of ecological habitat, we conducted infi ltration and redistribution experiments on three alluvial deposits in the Mojave National Preserve: (i) recently deposited active wash sediments, (ii) a soil of early Holocene age, and (iii) a highly developed soil of late Pleistocene age. At each, we ponded water in a 1-m-diameter infi ltration ring for 2.3 h and monitored soil water content and matric pressure during and atier infi ltration, using probes and electrical resistivity imaging (ERI). Infi ltration and downward fl ow rates were greater in younger material, favoring deep-rooted species. Deep-rooted species tend to colonize the margins of washes, where they are unaff ected by sediment transport that inhibits colonization. The ERI results support important generalizations, for example that shallower than 0.5 m, infi ltrated water persists longer in highly developed soil, favoring shallow-rooted species. Soil moisture data for the two youngest soils suggested that saturation overshoot, which may have signifi cant but unexplored hydroecologic and pedogenic eff ects, occurred at the horizontally advancing weting front. Spatial heterogeneity of soil properties generally increased with pedogenic development. Evidence suggested that some early-stage developmental processes may promote uniformity; the intermediate- age soil appeared to have the least heterogeneity in terms of textural variation with depth, and also the least anisotropy. Lateral heterogeneity was pronounced in older soil, having a multitude of eff ects on the distribution and retention of soil water, and may facilitate certain water-conserving strategies of plants over what would be possible in a laterally homogeneous soil. ?? Soil Science Society of America.

California↗
USGS2018

Ecohydrologic changes caused by hydrologic disconnection of ephemeral stream channels in Mojave National Preserve, California

Emplacement of highways and railroads has altered natural hydrologic systems by influencing surface-water flow paths and biotic communities in Mojave National Preserve. Infiltration experiments were conducted along active and abandoned channels to evaluate changes in hydrology and related effects on plant water availability and use. Simulated rainfall infiltration experiments with vegetation monitoring were conducted along an active channel upslope and a comparable abandoned channel down slope of the transportation corridor. We also conducted 90 single-ring, ponded infiltration experiments in adjacent channels to evaluate field-saturated hydraulic conductivity and particle size distributions. The abandoned channels are still morphologically evident, but are disconnected from runoff sources at higher elevations. Infiltration test results show that water infiltrates twice as fast in the active channels. Excavation showed weak soil development with fewer plant roots beneath the abandoned channel. SEM analysis on surface samples showed the presence of cyanobacteria only in abandoned channels. Plants up to three meters away from both channels showed physiological responses to channel water applied in a simulated pulse of rain. The response was short-lived and less pronounced for plants adjacent to the abandoned channel, whereas those adjacent to the active channel showed responses up to two months after the pulse. These responses may explain observed lower plant densities and fewer deep-rooted species along abandoned channels compared to active channels. We infer that the deeper-rooting plants are more abundant where they are able to take advantage of the increased soil-water storage resulting from greater infiltration and flow frequency in active stream channels.

California↗
USGS2016

Discovery of alunite in Cross crater, Terra Sirenum, Mars: Evidence for acidic, sulfurous waters

Cross crater is a 65 km impact crater, located in the Noachian highlands of the Terra Sirenum region of Mars (30°S, 158°W), which hosts aluminum phyllosilicate deposits first detected by the Observatoire pour la Minéralogie, L’Eau, les Glaces et l’Activitié (OMEGA) imaging spectrometer on Mars Express. Using high-resolution data from the Mars Reconnaissance Orbiter, we examine Cross crater’s basin-filling sedimentary deposits. Visible/shortwave infrared (VSWIR) spectra from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions diagnostic of alunite. Combining spectral data with high-resolution images, we map a large (10 km × 5 km) alunite-bearing deposit in southwest Cross crater, widespread kaolin-bearing sediments with variable amounts of alunite that are layered in <10 m scale beds, and silica- and/or montmorillonite-bearing deposits that occupy topographically lower, heavily fractured units. The secondary minerals are found at elevations ranging from 700 to 1550 m, forming a discontinuous ring along the crater wall beneath darker capping materials. The mineralogy inside Cross crater is different from that of the surrounding terrains and other martian basins, where Fe/Mg-phyllosilicates and Ca/Mg-sulfates are commonly found. Alunite in Cross crater indicates acidic, sulfurous waters at the time of its formation. Waters in Cross crater were likely supplied by regionally upwelling groundwaters as well as through an inlet valley from a small adjacent depression to the east, perhaps occasionally forming a lake or series of shallow playa lakes in the closed basin. Like nearby Columbus crater, Cross crater exhibits evidence for acid sulfate alteration, but the alteration in Cross is more extensive/complete. The large but localized occurrence of alunite suggests a localized, high-volume source of acidic waters or vapors, possibly supplied by sulfurous (H 2 S- and/or SO 2 -bearing) waters in contact with a magmatic source, upwelling steam or fluids through fracture zones. The unique, highly aluminous nature of the Cross crater deposits relative to other martian acid sulfate deposits indicates acid waters, high water throughput during alteration, atypically glassy and/or felsic materials, or a combination of these conditions.

American Mineralogist↗
USGS2016

One thousand years of fires: Integrating proxy and model data

The current fires raging across Indonesia are emitting more carbon than the annual fossil fuel emissions of Germany or Japan, and the fires are still consuming vast tracts of rainforest and peatlands. The National Interagency Fire Center (www.nifc.gov) notes that 2015 is one worst fire years on record in the U.S., where more than 9 million acres burned -- equivalent to the combined size of Massachusetts and New Jersey. The U.S. and Indonesian fires have already displaced tens of thousands of people, and their impacts on ecosystems are still unclear. In the case of Indonesia, the burning peat is destroying much of the existing soil, with unknown implications for the type of vegetation regrowth. Such large fires result from a combination of fire management practices, increasing anthropogenic land use, and a changing climate. The expected increase in fire activity in the upcoming decades has led to a surge in research trying to understand their causes, the factors that may have influenced similar times of fire activity in the past, and the implications of such fire activity in the future. Multiple types of complementary data provide information on the impacts of current fires and the extent of past fires. The wide array of data encompasses different spatial and temporal resolutions (Figure 1) and includes fire proxy information such as charcoal and tree ring fire scars, observational records, satellite products, modern emissions data, fire models within global land cover and vegetation models, and sociodemographic data for modeling past human land use and ignition frequency. Any single data type is more powerful when combined with another source of information. Merging model and proxy data enables analyses of how fire activity modifies vegetation distribution, air and water quality, and proximity to cities; these analyses in turn support land management decisions relating to conservation and development.

Frontiers of Biogeography↗
USGS1982

Seasonal growth in the bivalve Macoma balthica near the southern limit of its range

Shell-length growth in Macoma balthica from San Francisco Bay, California, as measured on living animals in situ, is highly seasonal despite a mild Mediterranean climate: a long period of near non-growth from May to the following February is followed by a short period of rapid growth between March and May. The rapid-growth period follows the spawning period during January/February and ends as water temperature rises above about 15??C. Despite the shortness of the growth period, M. balthica grows larger at a given age in San Francisco Bay than is recorded elsewhere in the world. Application of a model, developed elsewhere from these same field measurements, shows that (1) measurable growth occurs during the summer/autumn/early winter "nongrowth" period, (2) there is an autumn recruitment, and (3) both spring and autumn recruits combine to form a single "one-year-old" size grouping. None of these features is detectable through growth-ring analysis of field samples, apparently because of indistinct climatic seasons, or through size-frequency histogram analysis because of the combined effects of slow growth and intermittent recruitment. ?? 1982 Estuarine Research Federation.

Estuaries↗
USGS1995

Waterbird predation on fish in western Lake Erie: a bioenergetics model application

To better understand the role of piscivorous waterbirds in the food web of western Lake Erie, we applied a bioenergetics model to determine their total fish consumption, The important nesting species included the Herring Gull (Larus argentatus), Ring-billed Gull (L. delawarensis), Double-crested Cormorant (Phalacrocorax auritus), Great Blue Heron (Ardea herodias), Black-crowned Night-Heron (Nycticorax nycticorax), and Great Egret (Casmerodius albus). The impact of migrant waterbirds, including the Red-breasted Merganser (Mergus serrator), on western Lake Erie fish biomass was also considered in the analysis. According to the modeling results, during the early 1990s, piscivorous waterbirds consumed 13,368 tonnes of fish from western Lake Erie each year. This tonnage was equivalent to 15.2% of the prey fish biomass needed to support the walleye (Stizostedion vitreum) population in western Lake Erie during a single growing season. The model application was useful in quantifying energy flow between birds and fish in a large lake ecosystem.

Condor↗
USGS1991

Holocene Treeline Fluctuations in the Northern San Juan Mountains, Colorado, U.S.A., as Indicated by Radiocarbon-Dated Conifer Wood

An early to mid-Holocene warm period with greater than present-day monsoonal circulation is indicated by evidence in the northern San Juan Mountains of southwestern Colorado. Fifty radiocarbon ages of coniferous wood fragments, and several other radiocarbon ages of willow fragments, woody peat, and organic sediment associated with conifer remains, recovered from six sites at or above present-day treeline indicate that during the first half of the Holocene treeline was higher than present. Radiocarbon ages of coniferous wood fragments recovered from the remains of Lake Emma, a former glacial tarn above present-day treeline, indicate that between 9600 and 5400 BP treeline in the northern San Juan Mountains was at least 80 m higher than present. Furthermore, a radiocarbon age of a large spruce fragment with a complacent annual-ring record suggests that at about 8000 BP timberline may have been at least 140 m higher than present. These data suggest that during the early to mid-Holocene average July temperatures were at least 0.5 to 0.9°C higher than present. Radiocarbon ages and stratigraphy from bogs in the study area near present-day treeline suggest that between 5400 and 3500 BP treeline was near its present-day limits. After 3500 BP treeline was generally lower than present although short climatic ameliorations, with accompanying rises in treeline, may have occurred at about 3100 and 2400 BP. Deuterium concentrations previously determined for the cellulose of 18 conifer fragments from the Lake Emma site indicate a 70‰ decrease in deuterium from 9600 BP to present. These data indicate that the early Holocene increase in July solar radiation may have resulted in the intensification of the Arizona monsoon at that time.

Colorado↗
USGS1992

The oldest known Rocky Mountain bristlecone pines ( Pinus aristata Engelm.)

We have found 12 living Rocky Mountain bristlecone pines ( Pinus aristata ) more than 1600 yr old, including four that are more than 2100 yr old, on Black Mountain, near South Park, and on Almagre Mountain, in the southern Front Range, Colorado. A core from the oldest of these trees has an inner-ring date of 442 B.C. This tree is therefore at least 2435 yr old and exceeds the age of the oldest previously reported Rocky Mountain bristlecone pine by 846 yr. The ages of these trees show that Rocky Mountain bristlecone pines, under arid environmental conditions, achieve much older ages than have been previously reported. The ages also show that previously inferred trends in bristlecone pine ages, where maximum ages in the eastern range of Rocky Mountain bristlecone pines are much less than maximum ages in the western range of Great Basin bristlecone pines ( Pinus longaeva ), are less strong than previously supposed. Ancient Rocky Mountain bristlecone pines, such as those found in this study, have the potential to expand our knowledge of late Holocene climatic conditions in western North America.

Arctic and Alpine Research↗
USGS1966

Weather and pheasant populations in southwestern North Dakota

High productivity and survival of ring-necked pheasants ( Phasianus colchicus ) were correlated with high rainfall and cool temperatures in May and June during an 8-year period in southwestern North Dakota. These findings differed markedly from those of several earlier studies in the less arid midwestern United States where cool, wet weather in the spring generally affected pheasant populations adversely. General trends in the pheasant population could be explained on the basis of precipitation in May and June. The population was relatively high during the mid-1950's when wet and dry May and June periods occurred in alternate years but declined markedly after 2 consecutive years of spring and summer drought. The population remained at a static low during 1960 through 1963 when wet and dry spring and summer periods again occurred alternately.

North Dakota↗
USGS1970

Age determination of raccoons

Age criteria, based on 61 skulls and eye lenses from 103 known-age captives, are described for separating raccoons ( Procyon lotor ) into eight age-classes as follows: young-of-the-year, 1, 2, 3, 4, 5, 6-7, > 7 years. Criteria studied were eye lens nitrogen, cranial suture closure, tooth wear and incisor cementum layers. Lens nitrogen increased rapidly up to 12 months of age, but at much reduced rate thereafter. Total lens nitrogen was useful only in separating young-of-the-year from adults. The closure sequence for five cranial sutures accurately divided the total known-age sample of males into seven groups, and the adults into five groups. The tooth wear criteria divided the known-age sample into five relative age groups, but aging of individuals by this method was inaccurate. Histological sectioning of known-age teeth was the best method of observing layering in the cementum tissue. The technique of basing estimation of age on cementum ring counts, although subjective, was accurate for aging individuals through their fourth year but tended to underestimate the age of animals over 4 years old. However, suture closure or tooth wear can be used to identify males over 4 years old. In field studies, technical difficulties limit the utility of age estimation by cementum layers. Maximum root thickness of the lower canine was accurate in determining the sex of individuals from 5 months to at least 48 months of age.

Illinois↗
USGS1975

Long-term effects of 4-aminopyridine exposure to birds and fish

The avian frightening agent, 4-aminopyridine (4AP), was tested on five avian and two fish species to assess the effects of long-term 4AP exposure to nontarget vertebrates. Adult bobwhites ( Colinus virginianus ), mourning doves ( Zenaida macroura ), and ring-necked pheasants ( Phasianus colchicus ) were fed diets containing 3 percent 4AP-treated cracked corn diluted with various ratios of untreated corn for 7 to 35 days. Minimum dilution ratios that produced more than 50 percent mortality were 1:29 for bobwhites and 1:99 for doves. Mortality caused by 4AP could not be determined for pheasants because of their inability to subsist only on corn during the test periods. LCso's were determined for doves (316 ppm) and coturnix quail ( Coturnix coturnix ) (479 ppm) fed exclusively on uniformly treated laboratory rations for 28 to 40 days. Starlings ( Sturnus vulgaris ) treated by gavage daily for 25 days with 1.78 mg/kg 4AP showed no intoxication symptoms. Mortality in all avian species appeared to be the result of acute poisoning, and no evidence of cumulative toxicity was noted in species fed uniformly-treated rations. In 96-hour static tests, channel catfish ( Ictalurus punctatus ) and bluegill (Lepomis macrochirus) showed increasing sensitivity to 4AP with time in test waters ranging from very soft to very hard and from 12 to 22 C. The 96-hour LC 50 's for both species ranged from 2.43 to 7.56 mg/liter (ppm). Toxicity appeared to decrease with increasing water temperatures but was generally unaffected by water hardness. On the basis of the data presented, and the currently registered application rate for 4AP in agricultural crops (0.34 g/ha), long-term hazards to nontarget wildlife were judged to be minimal.

Colorado↗
USGS1997

Analysis of habitat selection studies with multiple patches within cover types

Current statistical methods are inadequate for evaluation of the relation between spatial pattern of the landscape and observed patterns of habitat use by individuals or populations. For example, traditional habitat selection analysis methods do not use information about the size and distribution of the several patches of each cover type that may exist within the study area. Statistical tests are presented for hypotheses about disproportional use of cover types and patches within cover types. These tests require that use of individual patches is recorded, as well as the size of individual patches. Different designs are considered in which there are (1) single or multiple samples of use, and (2) equal or unequal habitat availability. Formulas for calculating Type II statistical errors of the tests are presented and Monte Carlo simulation is used to assess the accuracy of the formulas and to check the Type I error rates of the proposed test statistics. With adequate sample sizes, Type II error formulas can be a useful tool for planning of habitat selection studies. An example analysis is presented of a hypothetical study of habitat selection by ring-necked pheasants ( Phasianus colchicus ) in a Midwestern landscape. The proposed tests also represent a contribution toward bringing together concepts of landscape ecology and wildlife habitat selection.

Journal of Wildlife Management↗
USGS2003

Short-term bird response to harvesting switchgrass for biomass in Iowa

The Conservation Reserve Program (CRP) provides habitat for grassland birds, but as contracts expire, some CRP fields might be returned to rowcrop production. One alternative to returning CRP fields to rowcrops is to produce switchgrass ( Panicum virgatum ) for use as a biomass fuel. Because the biomass is harvested during the fall and winter, breeding birds would not be directly affected by mowing the fields bur might be influenced by changes in vegetation structure resulting from the harvest. We evaluated bird abundances and nest success in totally harvested, partially harvested (alternating cut and uncut strips), and nonharvested CRP switchgrass fields in southern Iowa, USA, in 1999 and 2000. Species richness did not differ among harvest treatments. Abundances of most species (16 of 18) were not affected by the harvesting of switchgrass fields, and strip width did not affect bird numbers in strip-harvested fields. Grasshopper sparrows ( Ammodramus savannarum ) were more abundant in harvested portions of fields, and more sedge wrens ( Cistothorus platensis ) were recorded in nonharvested areas. The residual vegetation in nonharvested areas provided nest cover for species that begin nesting early in the season (e.g., northern harrier [Circus cyaneus] and ring-necked pheasant [ Phasianus colchicus ]). Nest success rates of grasshopper sparrows and common yellowthroats ( Geothlypis trichas ) were similar to those reported by other studies in switchgrass fields and might be sufficient to maintain stable populations. In general, switchgrass biomass fields create breeding habitat for some grassland birds, and a mixture of harvested and nonharvested fields would be more beneficial to grassland birds than totally harvesting or partially harvesting all switchgrass fields.

Iowa↗