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1.
Ecol Appl ; 16(4): 1529-38, 2006 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-16937816

RESUMEN

Populations of Greater Sage-Grouse (Centrocercus urophasianus) have declined by 69-99% from historic levels, and information on population dynamics of these birds at a landscape scale is essential to informed management. We examined the relationships between hen survival and a suite of landscape-scale habitat and environmental conditions. We radio-marked 237 female Sage-Grouse and measured 426 vegetation plots during 2001-2004 at four sites in a 3200-km2 landscape in north-central Montana, USA. We used program MARK to model monthly survival rates for 11 seasonal intervals. There was strong support for the best-approximating model (AICc weight = 0.810), which indicated that (1) hen survival varied by season within years and by year within seasons, (2) nesting hens had higher nesting-season survival than non-nesting hens, and (3) individuals at one site had lower hunting-season survival than at other sites. We observed considerable variation in hen survival. Process variation was 0.255, with an expected range of annual survival of 0.12 to 1.0. The ratio of process to total variation was 0.999, indicating that observed variation was real and not attributable to sampling variation. We observed a nearly fourfold difference in maximum and minimum annual survival, ranging from 0.962 +/- 0.024 (mean +/- SE) for nesting hens in 2001-2002 to 0.247 +/- 0.050) for non-nesters in 2003-2004. Low annual survival in 2003 resulted from the compounded effects of a West Nile virus outbreak in August and a severe winter in 2003-2004. Increased hen mortality associated with severe winter weather contrasts with prior beliefs that Sage-Grouse populations are typically unaffected by winter weather conditions and underscores the importance of protecting winter sagebrush (Artemisia spp.) habitats.


Asunto(s)
Galliformes/fisiología , Animales , Femenino , Modelos Biológicos , Montana , Dinámica Poblacional , Estaciones del Año , Tasa de Supervivencia , Factores de Tiempo
2.
Conserv Biol ; 20(2): 277-87, 2006 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-16903089

RESUMEN

In the 1990s the federal forests in the Pacific Northwest underwent the largest shift in management focus since their creation, from providing a sustained yield of timber to conserving biodiversity, with an emphasis on endangered species. Triggered by a legal challenge to the federal protection strategy for the Northern Spotted Owl (Strix occidentalis caurina), this shift was facilitated by a sequence of science assessments that culminated in the development of the Northwest Forest Plan. The plan, adopted in 1994, called for an extensive system of late-successional and riparian reserves along with some timber harvest on the intervening lands under a set of controls and safeguards. It has proven more successful in stopping actions harmful to conservation of old-growth forests and aquatic systems than in achieving restoration goals and economic and social goals. We make three suggestions that will allow the plan to achieve its goals: (1) recognize that the Northwest Forest Plan has evolved into an integrative conservation strategy, (2) conserve old-growth trees and forests wherever they occur and (3) manage federal forests as dynamic ecosystems.


Asunto(s)
Conservación de los Recursos Naturales/legislación & jurisprudencia , Conservación de los Recursos Naturales/métodos , Ecosistema , Agricultura Forestal/historia , Árboles , Agricultura Forestal/legislación & jurisprudencia , Historia del Siglo XX , Historia del Siglo XXI , Noroeste de Estados Unidos
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