Resumen. Las aves pueden esconder sus nidos de depredadores visuales localizándolos en sitios con cobertura y de depredados olfatorios donde las características del hábitat crean corrientes de aire, vientos fuertes o turbulencia atmosférica, pero los sitios con características óptimas para esconder los nidos de cada tipo de depredador generalmente son diferentes. Examinamos como Centrocercus urophasianus evalúa las necesidades de esconder sus nidos ante depredadores visuales y olfatorios en las montañas Parker, estado de Utah, donde el cuervo Corvus corax es el principal depredador visual mientras que los mamíferos Mephitis mephitis y Taxidea taxus son los principales depredadores olfatorios. Al comparar las características de los sitios de anidación con las de sitios al azar durante 2005 y 2006, encontramos que los nidos de C. urophasianus se encontraban escondidos de depredadores visuales pero que estaban expuestos a depredadores olfatorios. Para validar estos hallazgos, replicamos el estudio en el sudoeste de Wyoming en 2008. Nuevamente encontramos que la cobertura visual en los nidos era mayor que para sitios al azar, pero que la cobertura olfatoria era menor. Nuestros resultados indican que C. urophasianus selecciona los sitios de anidación con características que esconden los nidos de depredadores visuales pero a costa de localizar los nidos en sitios expuestos a depredadores olfatorios. En el sudoeste de Wyoming, encontramos que los depredadores olfatorios (mamíferos) y visuales (aves) depredaron la misma cantidad de nidos. Al seleccionar sitios de anidación con cobertura visual, C. urophasianus ha reducido el riesgo de depredación por depredadores visuales a un nivel similar al del riesgo impuesto por los depredadores olfatorios.Abstract. Birds can hide from visual predators by locating nests where there is cover and from olfactory predators where habitat features create updrafts, high winds, and atmospheric turbulence, but sites optimal for hiding from visual and olfactory predators often differ. We examined how Greater Sage-Grouse (Centrocercus urophasianus) balance the dual needs of hiding from both visual and olfactory predators on Parker Mountain, Utah, where the Common Raven (Corvus corax) is the main visual predator and the striped skunk (Mephitis mephitis) and American badger (Taxidea taxus) are the main olfactory predators. By comparing nest sites to random sites during 2005 and 2006, we found that sage-grouse nest at sites where their nests were obscured from visual predators but were exposed to olfactory predators. To validate these findings, we replicated the study in southwest Wyoming during 2008. Again, we found that visual obscurity at nest sites was greater than at control sites but olfactory obscurity was less. Our results indicate that Greater Sage-Grouse select nest sites where they will be concealed from visual predators but at the cost of locating nests where they are exposed to olfactory predators. In southwest Wyoming, we found that olfactory predators (mammals) and visual predators...
Survival of breeding-age hens has been identified as the demographic rate with the greatest potential to influence population growth of Greater Sage-Grouse (Centrocercus urophasianus (Bonaparte, 1827); hereafter "Sage-Grouse"). During 2008-2011, we collected summer survival data from 427 Sage-Grouse hens in southern Wyoming, USA. We assessed the effects of raptor densities, anthropogenic features, landscape features, and Sage-Grouse hen behavior on Sage-Grouse hen survival. Survival of Sage-Grouse hens was positively associated with the proportion of big sagebrush (genus Artemisia L.) habitat within 0.27 km radius and road density and negatively associated with power-line density, proximity to forested habitat, and topographic ruggedness index within 0.27 km radius (TRI 0.27 ). Raptor densities did not have individual effects on Sage-Grouse survival; however, an interaction between site-specific exposure to Golden Eagle (Aquila chrysaetos (L., 1758)) density (GOEA) and TRI 0.27 indicated that negative effects of GOEA and TRI 0.27 were dampened in areas with both high TRI 0.27 and high GOEA. Survival of nonreproductive hens was greater than brooding or nesting hens. Hens that stayed in intermediate-size flocks and yearling hens had higher survival than hens in small or large flocks and hens >2 years old. Results indicated that risk of death for Sage-Grouse hens was greater relative to potential raptor perches but not anthropogenic and landscape variables that could provide food subsidies for predators.Résumé : Il a été établi que la survie des femelles en âge de se reproduire constituait le taux démographique le plus susceptible d'influencer la croissance des populations de tétras des armoises (Centrocercus urophasianus (Bonaparte, 1827); ci-après « tétras »). De 2008 à 2011, nous avons recueilli des données sur la survie de 427 femelles de tétras dans le sud du Wyoming (États-Unis d'Amérique). Nous avons évalué les effets de la densité d'oiseaux de proie, d'éléments d'origine humaine, d'éléments du paysage et du comportement des tétras femelles sur la survie de ces dernières. La survie était positivement associée à la proportion de l'habitat d'armoises (genre Artemisia L.) dans un rayon de 0,27 km et à la densité des routes et négativement associée à la densité des lignes de transport électrique, la proximité d'habitats forestiers et l'indice d'irrégularité du relief dans un rayon de 0,27 km (TRI 0,27 ). Si la densité d'oiseaux de proie n'avait pas d'effet individuel sur la survie des tétras, une interaction entre l'exposition propre au site à la densité d'aigles royaux (Aquila chrysaetos (L., 1758)) (GOEA) et le TRI 0,27 indiquait que les effets négatifs de la GOEA et du TRI 0,27 étaient atténués dans les zones présentant un TRI 0,27 et une GOEA élevés. La survie des femelles non reproductrices était plus grande que celle des femelles couveuses ou nicheuses. Les femelles qui restaient dans des bandes de taille intermédiaire et les femelles de l'année avaient un meilleur taux de survie que les femelles dans des b...
Abstract.-Greater Sage-Grouse (Centrocercus urophasianus) have declined in distribution and abundance in western North America over the past century. Depredation of nests and predation of chicks can be two of the most influential factors limiting their productivity. Prey species utilize antipredation behaviors, such as predator avoidance, to reduce the risk of predation. Birds in general balance the dual necessity of selecting cover to hide from visual and olfactory predators to enhance prospects of survival and reproductive success, which may also be achieved by selecting habitat with relatively fewer predators. We compared avian predator densities at Greater Sage-Grouse nests and brood locations with those at random locations within available sagegrouse habitat in Wyoming. This comparison allowed us to assess the species' ability to avoid avian predators during nesting and early brood rearing. During -, we conducted -min point-count surveys at nests, brood locations from broods, and random locations. We found that random locations had higher densities of avian predators compared with nest and brood locations. Greater Sage-Grouse nested in areas where there were lower densities of Common Ravens (Corvus corax), Black-billed Magpies (Pica hudsonia), Golden Eagles (Aquila chrysaetos), and hawks (Buteo spp.) compared with random locations. Additionally, they selected brood-rearing locations with lower densities of those same avian predators and of American Kestrels (Falco sparverius), compared with random locations. By selecting nest and brood-rearing locations with lower avian predator densities, Greater Sage-Grouse may reduce the risk of nest depredation and predation on eggs, chicks, and hens. Received May , accepted June .Key words: avian predator, brood-site selection, Centrocercus urophasianus, Greater Sage-Grouse, nest-site selection, predation risk, predator avoidance, spatial autocorrelation. Centrocercus urophasianus Selecciona Sitios de Anidación y de Cría Lejos de Aves DepredadorasResumen.-El área de distribución y la abundancia de Centrocercus urophasianus han disminuido en el occidente de Norteamérica a lo largo del último siglo. La depredación de nidos y polluelos podría estar entre los factores que mayor influencia negativa han tenido sobre la productividad de la especie. Las presas presentan comportamientos antidepredatorios, como la evasión de los depredadores, para reducir el riesgo de depredación. Las aves en general compensan la necesidad de seleccionar un refugio para ocultarse de los depredadores visual y olfativamente con la necesidad de incrementar las probabilidades de supervivencia y éxito reproductivo, lo que también puede ser logrado seleccionando el hábitat con el menor número relativo de depredadores. Comparamos las densidades de depredadores alrededor de los nidos y sitios de cría de C. urophasianus con las densidades de depredadores de sitios escogidos al azar dentro del hábitat disponible para esta especie en Wyoming. Esta comparación nos permi...
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