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| Author | : Lamar B. Gore |
| Publisher | : |
| Total Pages | : 114 |
| Release | : 1999 |
| Genre | : Bobolink |
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| Total Pages | : |
| Release | : 2001 |
| Genre | : Birds |
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| Author | : Richard L. Schroeder |
| Publisher | : |
| Total Pages | : 22 |
| Release | : 1999 |
| Genre | : Grasses |
| ISBN | : |
National Wildlife Refuges are required to manage habitat in accord with an approved Comprehensive Conservation Plan containing specific measureable habitat objectives. Tallgrass pririe habitat is of critical concern at the Tewaukon National Wildlife Refuge. Habitat management directed at improving conditions for declining bird species, rare butterflies, and a diversity of tallgrass flora is assumed to contribute substantially toward the broad goal of maintaining native biodiversity in tallgrass priries. Such management should consider the size of tallgrass patches, the amount of woody vegetation, providing a mosaic of vegetation heights, and improving overall floristic quality. Selection of appropriate management strategies followed by monitoring and evaluation of habitat conditions will allow for adaptive management and appropriate modifications over time.
| Author | : |
| Publisher | : |
| Total Pages | : 40 |
| Release | : 2002 |
| Genre | : Birds |
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| Author | : Paul D. Goriup |
| Publisher | : International |
| Total Pages | : 268 |
| Release | : 1988 |
| Genre | : Nature |
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| Author | : Peter D. Vickery |
| Publisher | : |
| Total Pages | : 312 |
| Release | : 1999 |
| Genre | : Nature |
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| Author | : Torre James Hovick |
| Publisher | : |
| Total Pages | : 128 |
| Release | : 2014 |
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Grasslands are inherently dynamic in space and time evolving with frequent disturbance from fire and herbivores. Throughout much of the world, grasslands have been converted and fragmented and many remaining grasslands have become homogenous as a consequence of human actions. As a result, ecosystem function has declined and biodiversity loss has led to decreased ecological services. Of particular concern are highly imperiled grassland birds which have experienced greater population declines than any other habitat associated guild of birds in North America. Conservation efforts that restore heterogeneity to grasslands through the re-coupling of fire and grazing may be an effective strategy for stabilizing or increasing grassland bird populations. We examined Greater Prairie-Chicken (Tympanuchus cupido) ecology, breeding bird community diversity and stability, and non-breeding bird community diversity and patch occupancy in tallgrass prairie with restored structural and compositional heterogeneity. We found that Greater Prairie-Chickens selected for patches with greater time since fire and grazing and that taller vegetation increased nest survival. Additionally, nests that survived were in cooler environments and prairie-chickens displayed fine scale thermal habitat selection as nest sites were nearly 4°C cooler than micro-sites within 2 meters of nests. We found that heterogeneity increased breeding bird community diversity and that increased heterogeneity resulted in greater community stability over time. Finally, non-breeding bird community diversity increased as a result of structural heterogeneity and occupancy modeling revealed that certain species selected for varying patches along a disturbance gradient (i.e, recently disturbed to relatively undisturbed) that resulted from fire and grazing dependent heterogeneity. Our findings add to a growing body of literature supporting the use of fire and grazing to create a shifting grassland mosaic that increases vegetation structural and compositional heterogeneity and maximizes native biodiversity within rangeland ecosystems through the conservation of natural patterns and processes. Additionally, these data provide evidence that variation in grassland structure resulting from the fire-grazing interaction may be important in moderating thermal environments and highlights the complex and interactive effects of restored ecological processes on ecosystems. We recommend future management efforts in rangelands focus on restored disturbance process to increase heterogeneity and improve grassland bird conservation.
| Author | : Bram Hendrik Ferdinand Verheijen |
| Publisher | : |
| Total Pages | : |
| Release | : 2017 |
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Grasslands are among the most rapidly declining ecosystems in the world. The Flint Hills ecoregion contains one of the largest remaining tracts of tallgrass prairie, but most of the area is managed with high densities of grazing animals and frequent prescribed burns, thereby reducing variation in vegetative structure. A homogeneous landscape leads to lower diversity and abundance of wildlife species, including grassland songbirds. Patch-burn grazing management has been proposed to more closely match the historical interaction between fire and selective grazing by native ungulates. Pastures managed with patch-burn grazing have a greater variety of vegetative structure and plant species composition, and as a result, higher species diversity, abundance, and reproductive success of grassland birds. However, past work has not considered potential effects of regional variation in predation risk and rates of brood parasitism by Brown-headed Cowbirds (Molothrus ater), or annual variation in climatic conditions on the effects of patch-burn grazing management on the reproductive success of grassland songbirds. Over a six year period and at two tallgrass prairie sites, I tested the effects of patch-burn grazing on the reproductive success of three native grassland songbird species, Dickcissels (Spiza americana), Eastern Meadowlarks (Sturnella magna), and Grasshopper Sparrows (Ammodramus savannarum), as well as subsequent effects on the space use, movements, and survival of fledgling Dickcissels. I found only minor effects of patch-burn grazing on the reproductive success of grassland songbirds, supporting previous studies that show that patch-burn grazing does not have negative effects on demographic rates of grassland songbirds. Management regime did not affect densities or territory size of male Dickcissels, but bird densities tended to be higher and territories tended to be smaller on patches within the patch-burn grazing treatment that were burned in the previous year. Thus, patch-burn grazing management might benefit Dickcissel populations by providing higher quality breeding habitat in unburned patches. Last, I found evidence for a potential tradeoff between habitat selection for nests vs. fledglings of Dickcissels in some rangeland management strategies. Parents that realized high reproductive success by nesting in pastures with lower cowbird densities, produced fledglings that faced high rates of depredation by snakes and showed greater movements away from those pastures. Survival rates and movements of Dickcissel fledglings were low, especially during the first week after leaving the nest, which stresses the importance of local habitat conditions. At a larger spatial scale, I tested whether regional differences in habitat structure could drive variation in apparent survival of grassland songbirds. I found that grassland- and shrubland-breeding species had higher estimates of apparent survival than forest-breeding species, contrary to the prevailing viewpoint that birds breeding in dynamic landscapes, such as frequently burned grasslands, should show lower apparent survival than species that breed in woody habitats. The results of my field study show that restoring the historical interaction between fire and grazing on the landscape via patch-burn grazing management could benefit grassland songbirds. Moreover, my dissertation is the first study that tests the effects of patch-burn grazing management on the survival and movements of fledgling Dickcissels, and shows that high cowbird densities can cause a tradeoff between different life-stages. Future conservation efforts should take into account regional variation in species abundance, predator community composition and abundance of Brown-headed Cowbirds when assessing the effects of rangeland management on the demography of grassland songbirds.
| Author | : Elizabeth Marie Madden |
| Publisher | : |
| Total Pages | : 306 |
| Release | : 1996 |
| Genre | : Passeriformes |
| ISBN | : |
To more effectively manage remaining native grasslands and declining populations of prairie passerine birds, linkages between disturbance regimes, vegetation, and bird abundance need to be more fully understood. Therefore I examined bird-habitat relationships on northern mixed-grass prairie at Lostwood National Wildlife Refuge in northwestern North Dakota, where prescribed fire has been used as a habitat management tool since the 1970's. I sampled bird abundance on upland prairie at 310 point count locations during 1993 and 1994 breeding seasons. I then measured vegetation structure and composition at each location. Complete fire histories were available for each point, with over 80% being burned 1 to 4 times in the last 15 years. Striking differences in bird species abundance were apparent among areas with different fire histories. Baird's, grasshopper, and Le Conte's sparrows,Sprague's pipits, bobolinks, and western meadowlarks were absent from unburned prairie, but were among the.
| Author | : Benjamin S. Thatcher |
| Publisher | : |
| Total Pages | : 270 |
| Release | : 2007 |
| Genre | : Bird populations |
| ISBN | : |
Partners in Flight (PIF) recommends using silviculture to improve breeding habitat conditions for migrant landbirds. Alternative thinning treatments may benefit priority landbird species by increasing structural complexity in second-growth forests. However, the effects of thinning on landbird populations in oak (Quercus spp.)-hickory (Carya spp.) forests have not been experimentally demonstrated. I used a randomized and replicated large-scale manipulative experiment to evaluate the effects of thinning (i.e., crown-release and gap creation) on forest habitat characteristics and avian populations at the Tennessee National Wildlife Refuge. I collected data during 2001 (pre-treatment) and from 2002 to 2005 (1 to 4 years post-treatment) in 20-ha thinned (n = 8) and control (n = 4) plots. Using mixed model ANOVA with covariates, I compared habitat attributes, tree regeneration, avian population densities, daily nest survival rates, realized brood sizes (# fledged per successful nest), rates of brown-headed cowbird (Molothrus ater) brood parasitism, and nest-site characteristics between treatments. In addition, I used Program MARK to evaluate the influence of habitat factors at multiple spatial scales on predation rates of Acadian flycatcher (Empidonax virescens) and wood thrush (Hylocichla mustelina) nests. Forest habitat attributes, avian population densities, and nest survival rates did not differ between control and thinned plots prior to treatment, indicating my experimental design (including the random allocation of treatments to plots, blocking, and the interspersion of plots across the study area) was sufficient for detecting treatment effects. Thinning resulted in a 29% difference in basal area between treatments (thinned = 20.3 m2 ha−1; control = 28.5 m2 ha−1). Compared to controls, thinned plots had significantly less overstory cover and midstory cover and significantly more downed wood and herbaceous and woody vegetation in the lower forest strata. Specifically, I detected greater densities of oak (Quercus spp.), yellow-poplar (Liriodendron tulipifera), and sourwood (Oxydenrum arboretum) saplings, and greater cover in poison ivy (Toxicodendron radicans) and blackberry (Rubus spp.) in thinned than control plots. I used spot-mapping to estimate the densities of PIF priority species. Thinning had positive effects on the densities of seven species (eastern towhee [Pipilo erythropthalmus], eastern-wood pewee [Contopus virens], indigo bunting [Passerina cyanea], Kentucky warbler [Oporornis formosus], white-eyed vireo [Vireo griseus], yellow-breasted chat [Icteria virens], and yellow-throated vireo [Vireo flavifrons]), inconclusive or negligible effects on the densities of two species (Louisiana waterthrush [Seiurus motacilla] and worm-eating warbler [Helmitheros vermivorus]), and negative effects on the densities of two species (Acadian flycatcher and wood thrush). I monitored 1,149 nests of 28 species. Predation accounted for 80% of all nest failures. Mayfield-adjusted nest daily survival rates of all species combined did not significantly differ between treatments. For all species combined, rates of cowbird parasitism varied annually but did not significantly differ between thinned (20.8%, SE = 2.3) and control (18.5%, SE = 3.7) plots. I assigned bird species to functional groups for further analyses. PIF priority mature-forest species exhibited nest daily survival rates (0.972 vs. 0.969), realized brood sizes (2.8 vs. 2.6), and parasitism rates (16.9 vs. 10.4%) that were comparable between thinned and control plots. Based on 162 nests in thinned plots, PIF shrubland species had nest daily survival rates of 0.958, realized brood sizes of 2.9, and parasitism rates of 13.6%; this functional group nested too rarely in control plots for analysis. Treatment effects were significant for the overstory and midstory nesting functional groups. Overstory nesters exhibited nest daily survival rates that were greater in thinned (0.982) than control (0.963) plots. Midstory nesters experienced greater parasitism rates in thinned (30.0%) than control (17.9%) plots. I evaluated nest-site selection and factors affecting nest predation rates using 132 Acadian flycatcher and 112 wood thrush nests. In thinned plots, both species selected nest sites with greater overstory and midstory cover than found at random. I found little evidence that nest predation rates were influenced by the amount of agriculture in the local (314 ha) landscape or by distance to anthropogenic edge, perhaps because the landscape was predominantly forested (agriculture [less-than or equal to] 4%) and most nests were>350 m from an edge. In thinned plots, predation rates on wood thrush nests decreased with increasing overstory cover and increasing basal area in large trees; predation rates increased with increasing basal area in small-diameter trees. None of the habitat predictors I measured had a strong relationship to Acadian flycatcher nest predation rates in thinned or control plots. Model-averaged nest survival estimates for wood thrushes were 27.8% and 26.8% in thinned and control plots, respectively. Acadian flycatcher model-averaged nest survival estimates were 53.5% in thinned and 56.4% in control plots. In summary, my results indicate that thinning had strong effects on forest habitat attributes and the demographics of some priority bird species. In the short term (1 to 4 years post-treatment), thinning appears to provide suitable breeding habitat for priority bird species that prefer dense understory vegetation or partially-opened overstories for nesting. Conversely, thinning had neutral or negative effects on some species and functional groups that nest in midstory vegetation, indicating there may be an ecological cost, in the short-term, associated with implementing this treatment. This treatment likely will have differential costs and benefits for avian populations as forest habitat conditions continue responding via successional dynamics and vegetative growth to the initial thinning operation.
