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1 March 2013 Survival and Home-range Size of Northern Spotted Owls in Southwestern Oregon
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Abstract

In the Klamath province of southwestern Oregon, Northern Spotted Owls (Strix occidentalis caurina) occur in complex, productive forests that historically supported frequent fires of variable severity. However, little is known about the relationships between Spotted Owl survival and home-range size and the characteristics of fire-prone, mixed-conifer forests of the Klamath province. Thus, the objectives of this study were to estimate monthly survival rates and home-range size in relation to habitat characteristics for Northern Spotted Owls in southwestern Oregon. Home-range size and survival of 15 Northern Spotted Owls was monitored using radiotelemetry in the Ashland Ranger District of the Rogue River–Siskiyou National Forest from September 2006 to October 2008. Habitat classes within Spotted Owl home ranges were characterized using a remote-sensed vegetation map of the study area. Estimates of monthly survival ranged from 0.89 to 1.0 and were positively correlated with the number of late-seral habitat patches and the amount of edge, and negatively correlated with the mean nearest neighbor distance between late-seral habitats. Annual home-range size varied from to 189 to 894 ha (  =  576; SE  =  75), with little difference between breeding and nonbreeding home ranges. Breeding-season home-range size increased with the amount of hard edge, and the amount of old and mature forest combined. Core area, annual and nonbreeding season home-range sizes all increased with increased amounts of hard edge, suggesting that increased fragmentation is associated with larger core and home-range sizes. Although no effect of the amount of late-seral stage forest on either survival or home-range size was detected, these results are the first to concurrently demonstrate increased forest fragmentation with decreased survival and increased home-range size of Northern Spotted Owls.

En la provincia de Klamath, al suroeste de Oregón, Strix occidentalis caurina habita bosques complejos y productivos que históricamente han soportado incendios frecuentes de intensidad variable. Sin embargo, se sabe poco acerca de las relaciones entre la supervivencia de S. o. caurina y el tamaño del área de acción y las características de los bosques mixtos de coníferas propensos a incendios de la provincia de Klamath. Por ello, los objetivos de este estudio fueron estimar las tasas de supervivencia mensuales y el tamaño del área de acción en relación con las características del hábitat de S. o. caurina en el suroeste de Oregón. Se monitorearon el área de acción y la supervivencia de 15 individuos de S. o. caurina usando radiotelemetría en el Distrito de Guardabosque Ashland del Bosque Nacional Rogue River–Siskiyou desde septiembre del 2006 a octubre del 2008. Las clases de hábitat dentro de las áreas de acción de S. o. caurina fueron caracterizadas usando un mapa de vegetación del área de estudio elaborado con sensores remotos. Las estimaciones de supervivencia mensual oscilaron entre 0.89 y 1.0 y estuvieron positivamente correlacionadas con el número de parches de hábitat de la etapa sucesional tardía y la cantidad de hábitat de borde, y negativamente correlacionados con la distancia media al vecino más cercano entre hábitats sucesionales tardíos. El área de acción anual varió de 189 a 894 ha (  =  576; EE  =  75), con una pequeña diferencia entre las áreas de acción reproductivas y no reproductivas. El área de acció

The Raptor Research Foundation, Inc.
Jason W. Schilling, Katie M. Dugger, and Robert G. Anthony "Survival and Home-range Size of Northern Spotted Owls in Southwestern Oregon," Journal of Raptor Research 47(1), 1-14, (1 March 2013). https://doi.org/10.3356/JRR-11-76.1
Received: 11 October 2011; Accepted: 1 September 2012; Published: 1 March 2013
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