80 resultados para Hawks
Resumo:
For hundreds of years black-tailed prairie dogs inhabited the Great Plains by the millions, improving the grazing for bison and pronghorn antelope, digging escape holes and homes for burrowing owls and rodents, and serving as prey for badgers, coyotes, hawks, and bobcats. This book by the renowned naturalist and writer Paul A. Johnsgard tells the complex biological and environmental story of the western Great Plains under the prairie dog’s reign—and then under a brief but devastating century of human dominion. An indispensable and highly readable introduction to the ecosystem of the shortgrass prairie, Prairie Dog Empire describes in clear and detailed terms the habitat and habits of black-tailed prairie dogs; their subsistence, seasonal behavior, and the makeup of their vast colonies; and the ways in which their “towns” transform the surrounding terrain—for better or worse. Johnsgard recounts how this terrain was in turn transformed over the past century by the destruction of prairie dogs and their grassland habitats, together with the removal of the bison and their replacement with domestic livestock. A disturbing look at profound ecological alterations in the environment, this book also offers a rare and invaluable close-up view of the rich history and threatened future of the creature once considered the “keystone” species of the western plains. Included are maps, drawings, and listings of more than two hundred natural grassland preserves where many of the region’s native plants and animals may still be seen and studied. This excerpt includes the Preface and Chapter 1, "The Western Shortgrass Prairie: A Brief History."
Resumo:
Let me begin today by thanking you, Regent Hassebrook, as Task Force Chair, and each of you who is a member of this Task Force, for focusing on outreach and economic development at the University as we work on behalf of Nebraska. We thank Regent Chair Howard Hawks for appointing this task force. The level of commitment this shows for the university's role in outreach and economic development is very important both to us in the university and to Nebraskans.
Resumo:
As you can see from the general tenor of the printed program for this seminar, I am in the unenviable position of trying to discourage you from certain types of chemical control; but my assigned topic "Side Effects of Persistent Toxicants," implies that mission. However, my remarks may be somewhat anticlimax at this time, because it is now generally conceded that we need to reevaluate certain chemicals in control work and to restrict or severely curtail use of those that per¬sist for long periods in the environment. So let me detail my reasons for a somewhat negative attitude toward the use of the persistent hydrocarbons from my experience with the effects of these materials on birds. But first a few words of caution about control work in general, which so often disrupts natural processes and leads to new and unforseen difficulties. As an example, I think of the irruption of mice in the Klamath valley in northern California and southern Oregon in the late '50's. Intensive predator control, particularly of coyotes, but also of hawks and owls, was followed by a severe outbreak of mice in the spring of 1958. To combat the plague of mice, poisoned bait (1080 and zinc phosphide) was widely distributed in an area used by 500,000 waterfowl each spring. More than 3,000 geese were poisoned, so driv¬ing parties were organized to keep the geese off the treated fields. Here it seems conceivable that the whole chain of costly events--cost of the original and probably unnecessary predator control, economic loss to crops from the mouse outbreak, another poisoning campaign to combat the mice, loss of valuable waterfowl resources, and man-hours involved in flushing geese from the fields--might have been averted by a policy of not interfering with the original predator-prey relationship. This points to a dilemma we always face. (We create deplorable situations by clumsy interference with natural processes, then seek artificial cures to correct our mistakes.) For example, we spend millions of dollars in seeking cures for cancer, but do little or nothing about restricting the use of known or suspected carcinogens such as nicotine and DDT.
Resumo:
Abstract Background The family Accipitridae (hawks, eagles and Old World vultures) represents a large radiation of predatory birds with an almost global distribution, although most species of this family occur in the Neotropics. Despite great morphological and ecological diversity, the evolutionary relationships in the family have been poorly explored at all taxonomic levels. Using sequences from four mitochondrial genes (12S, ATP8, ATP6, and ND6), we reconstructed the phylogeny of the Neotropical forest hawk genus Leucopternis and most of the allied genera of Neotropical buteonines. Our goals were to infer the evolutionary relationships among species of Leucopternis, estimate their relationships to other buteonine genera, evaluate the phylogenetic significance of the white and black plumage patterns common to most Leucopternis species, and assess general patterns of diversification of the group with respect to species' affiliations with Neotropical regions and habitats. Results Our molecular phylogeny for the genus Leucopternis and its allies disagrees sharply with traditional taxonomic arrangements for the group, and we present new hypotheses of relationships for a number of species. The mtDNA phylogenetic trees derived from analysis of the combined data posit a polyphyletic relationship among species of Leucopternis, Buteogallus and Buteo. Three highly supported clades containing Leucopternis species were recovered in our phylogenetic reconstructions. The first clade consisted of the sister pairs L. lacernulatus and Buteogallus meridionalis, and Buteogallus urubitinga and Harpyhaliaetus coronatus, in addition to L. schistaceus and L. plumbeus. The second clade included the sister pair Leucopternis albicollis and L. occidentalis as well as L. polionotus. The third lineage comprised the sister pair L. melanops and L. kuhli, in addition to L. semiplumbeus and Buteo buteo. According to our results, the white and black plumage patterns have evolved at least twice in the group. Furthermore, species found to the east and west of the Andes (cis-Andean and trans-Andean, respectively) are not reciprocally monophyletic, nor are forest and non-forest species. Conclusion The polyphyly of Leucopternis, Buteogallus and Buteo establishes a lack of concordance of current Accipitridae taxonomy with the mtDNA phylogeny for the group, and points to the need for further phylogenetic analysis at all taxonomic levels in the family as also suggested by other recent analyses. Habitat shifts, as well as cis- and trans-Andean disjunctions, took place more than once during buteonine diversification in the Neotropical region. Overemphasis of the black and white plumage patterns has led to questionable conclusions regarding the relationships of Leucopternis species, and suggests more generally that plumage characters should be used with considerable caution in the taxonomic evaluation of the Accipitridae.
Resumo:
La referencia a las aves de caza presente en el comienzo del CMC opera a modo de "anclaje" que nos anticipa que los eventos y sucesos del poema se desarrollarán en un entorno exclusivamente nobiliario. Asimismo la ausencia de halcones y azores nos habla de una situación de privación que afecta no sólo al Cid en cuanto a sus bienes, sino también, teniendo en cuenta el valor simbólico de las aves, a su honor en todos sus aspectos. En cuanto al por qué de la ausencia de escenas de caza en el Cantar, podemos aventurar tres razones concomitantes: a) funciona como una tácita crítica dirigida contra los usos de la nobleza cortesana y asimismo indica el alejamiento del Cid respecto de dicho entorno; b) señala la clausura del ocio estamental del Cid y los suyos; c) es un índice de la paulatina incorporación de prácticas y restricciones monásticas por parte del estamento nobiliario, en el marco de la "monaquización" de los bellatores.
Resumo:
La referencia a las aves de caza presente en el comienzo del CMC opera a modo de "anclaje" que nos anticipa que los eventos y sucesos del poema se desarrollarán en un entorno exclusivamente nobiliario. Asimismo la ausencia de halcones y azores nos habla de una situación de privación que afecta no sólo al Cid en cuanto a sus bienes, sino también, teniendo en cuenta el valor simbólico de las aves, a su honor en todos sus aspectos. En cuanto al por qué de la ausencia de escenas de caza en el Cantar, podemos aventurar tres razones concomitantes: a) funciona como una tácita crítica dirigida contra los usos de la nobleza cortesana y asimismo indica el alejamiento del Cid respecto de dicho entorno; b) señala la clausura del ocio estamental del Cid y los suyos; c) es un índice de la paulatina incorporación de prácticas y restricciones monásticas por parte del estamento nobiliario, en el marco de la "monaquización" de los bellatores.
Resumo:
La referencia a las aves de caza presente en el comienzo del CMC opera a modo de "anclaje" que nos anticipa que los eventos y sucesos del poema se desarrollarán en un entorno exclusivamente nobiliario. Asimismo la ausencia de halcones y azores nos habla de una situación de privación que afecta no sólo al Cid en cuanto a sus bienes, sino también, teniendo en cuenta el valor simbólico de las aves, a su honor en todos sus aspectos. En cuanto al por qué de la ausencia de escenas de caza en el Cantar, podemos aventurar tres razones concomitantes: a) funciona como una tácita crítica dirigida contra los usos de la nobleza cortesana y asimismo indica el alejamiento del Cid respecto de dicho entorno; b) señala la clausura del ocio estamental del Cid y los suyos; c) es un índice de la paulatina incorporación de prácticas y restricciones monásticas por parte del estamento nobiliario, en el marco de la "monaquización" de los bellatores.