scholarly journals Temporal Variation in the Vital Rates of an Insular Population of Spotted Owls (Strix Occidentalis Occidentalis): Contrasting Effects of Weather

The Auk ◽  
2004 ◽  
Vol 121 (4) ◽  
pp. 1056-1069
Author(s):  
William S. LaHaye ◽  
Guthrie S. Zimmerman ◽  
R. J. Gutiérrez
Keyword(s):  
Temporal Variation ◽  
Breeding Season ◽  
Process Variation ◽  
Meta Analysis ◽  
First Year ◽  
Spotted Owl ◽  
Strix Occidentalis ◽  
Adult Females ◽  
Temporal Process ◽  
Spotted Owls

Abstract We studied the demography of an insular California Spotted Owl (Strix occidentalis occidentalis) population in southern California for 12 years. We used model selection based on information theory to examine the relationship between weather and reproduction and survival. Mean annual fecundity was 0.139 (SE = 0.050) for subadult females and 0.345 (SE = 0.028) for adult females. Adult females had higher fecundity than subadult females during all years, and fecundity in both age classes was higher when a wet year preceded a dry spring (i.e. breeding season). A model incorporating these factors explained 100% of the estimated temporal process variation in fecundity. Mean apparent survival was 0.796 (SE = 0.012), 0.880 (SE = 0.041), 0.692 (SE = 0.062), and 0.368 (SE = 0.038) for adult, second-year subadult, first-year subadult, and juvenile (first-year) owls, respectively. We found no temporal process variation in survival. Using a Leslie projection matrix, we estimated the finite rate of population change to be 0.906 (SE = 0.018) over the entire period of study (1987–1998), which indicated that the population declined ≈9% per year during the study. That rate of decline was higher than a rate (λ1991–1998 = 0.921, SE = 0.020) we estimated for a shorter period (1991–1998) that matched the time interval used in a recent meta-analysis of Spotted Owl population dynamics. We believe that both the present estimates and those of the meta-analysis are valid, given their respective goals. The study population was characterized by relatively high, constant survival of territorial birds, low and variable annual reproduction, and relatively low juvenile survival. Because weather was strongly correlated with reproduction, fecundity rates for the species may decline during short-term droughts and when storms occur during the breeding season. Weather extremes may not, however, be sufficient to affect temporal variation in survival of Spotted Owls in this part of their range.

scholarly journals Does The Presence of Barred Owls Suppress the Calling Behavior of Spotted Owls?

The Condor ◽  
2006 ◽  
Vol 108 (4) ◽  
pp. 760-769 ◽  
Author(s):  
Michelle L. Crozier ◽  
Mark E. Seamans ◽  
R. J. GutiÉRrez ◽  
Peter J. Loschl ◽  
Robert B. Horn ◽  
...  
Keyword(s):  
Calling Behavior ◽  
Field Observations ◽  
Spotted Owl ◽  
Strix Occidentalis ◽  
Response Data ◽  
Strix Varia ◽  
Spotted Owls ◽  
Strix Occidentalis Caurina ◽  
Northern Spotted Owls ◽  
Barred Owls

Abstract Abstract Barred Owls (Strix varia) have expanded their range throughout the ranges of Northern (Strix occidentalis caurina) and California Spotted Owls (S. o. occidentalis). Field observations have suggested that Barred Owls may be behaviorally dominant to Spotted Owls. Therefore, we conducted a test of behavioral dominance by assessing responsiveness of Spotted Owls to conspecific calls when they were in the simulated presence (i.e., imitation of Barred Owl vocalizations) of a Barred Owl. We hypothesized that Spotted Owls would be less likely to respond to conspecific calls in areas where Barred Owls were common. We used a binary 2 × 2 crossover experimental design to examine male Spotted Owl responses at 10 territories randomly selected within two study areas that differed in abundance of Barred Owls. We also conducted a quasi experiment at four study areas using response data from any Spotted Owl (male or female) detected following exposure to Barred Owl calls. We inferred from the crossover experiment that the simulated presence of a Barred Owl might negatively affect Spotted Owl responsiveness. Both subspecies of Spotted Owl responded less to Spotted Owl calls after exposure to Barred Owl calls, Northern Spotted Owls responded less frequently in areas having higher numbers of Barred Owls, and California Spotted Owls responded less frequently than Northern Spotted Owls overall.

scholarly journals Are Barred Owls Displacing Spotted Owls?

The Condor ◽  
2003 ◽  
Vol 105 (1) ◽  
pp. 45-53 ◽  
Author(s):  
Elizabeth G. Kelly ◽  
Eric D. Forsman ◽  
Robert G. Anthony
Keyword(s):  
Pacific Northwest ◽  
Current Status ◽  
Spotted Owl ◽  
Strix Occidentalis ◽  
Strix Varia ◽  
The Pacific ◽  
Spotted Owls ◽  
Before And After ◽  
Strix Occidentalis Caurina ◽  
Barred Owls

Abstract Barred Owls (Strix varia) have expanded their range into the Pacific Northwest, and anecdotal evidence suggests that they may be displacing the federally threatened Northern Spotted Owl (Strix occidentalis caurina). Our objectives were to describe the current status of Barred Owls in Oregon and compare occupancy of Spotted Owls in historic Spotted Owl territories before and after Barred Owls were first detected in those territories. Between 1974 and 1998, we estimated that 706 different Barred Owl territories were located in Oregon. From 1989–1998 an average of 60 new Barred Owl territories were located in Oregon each year. In Spotted Owl demographic study areas in Oregon and Washington, Barred Owl detections increased at Spotted Owl territories from 1987–1999. Occupancy of Spotted Owl territories declined after Barred Owls were detected within 0.80 km of the territory center. When Barred Owls were detected 0.81–2.40 km from Spotted Owl territory centers, occupancy of Spotted Owls was only marginally less than at territories without Barred Owls. This suggests that the frequency and intensity of interactions between the two species is negatively associated with distance between them. Our results suggest that land managers and regulatory agencies should regard Barred Owls as a threat to Spotted Owls, particularly if Barred Owls continue to increase in number as they have during the past 25 years. ¿Está Strix varia Desplazando a Strix occidentalis caurina? Resumen. Desde su expansión hacia el Pacífico Noroeste, existe evidencia anecdótica de que Strix varia podría estar desplazando a S. occidentalis caurina. Nuestros objetivos fueron describir el estatus actual de S. varia en Oregon y comparar la ocurrencia de S. occidentalis caurina en sus territorios históricos antes y después de que S. varia se detectó por primera vez en dichos territorios. Entre 1974 y 1998, estimamos que se confirmaron 706 territorios diferentes de S. varia en Oregon. Entre 1989 y 1998, se localizaron en promedio 60 nuevos territorios de S. varia anualmente. En áreas con estudios demográficos de S. occidentalis caurina en Oregon y Washington, las detecciones de S. varia en territorios de S. occidentalis caurina se incrementaron entre 1987 y 1999. En comparación con territorios sin S. varia, la ocupación de territorios de S. occidentalis caurina disminuyó luego de que se detectaron individuos de S. varia a menos de 0.80 km del centro del territorio. Cuando se detectaron individuos de S. varia entre 0.81 y 2.40 km del centro de los territorios, la ocupación de éstos fue sólo marginalmente menor que en territorios sin S. varia. Esto sugiere que la frecuencia e intensidad de la interacción entre las dos especies está asociada con la distancia entre ellas. Nuestros resultados sugieren que las autoridades ambientales y de regulación deben considerar a S. varia como una amenaza para S. occidentalis caurina, particularmente si los números de S. varia se siguen incrementando como en los últimos 25 años.

scholarly journals Breeding Dispersal In the California Spotted Owl

The Condor ◽  
2006 ◽  
Vol 108 (1) ◽  
pp. 71-81 ◽  
Author(s):  
Jennifer A. Blakesley ◽  
David R. Anderson ◽  
Barry R. Noon
Keyword(s):  
A Priori ◽  
Dispersal Distance ◽  
Breeding Dispersal ◽  
Territory Quality ◽  
Spotted Owl ◽  
Factors Associated ◽  
Strix Occidentalis ◽  
Spotted Owls ◽  
California Spotted Owl ◽  
Dispersal Probability

Abstract Spotted Owls (Strix occidentalis) are territorial, generally nonmigratory, and strongly philopatric. Nevertheless, California Spotted Owls (S. o. occidentalis) exhibited breeding dispersal during 7% of interannual observations of banded individuals (n = 54 of 743 occasions). Based on ecological theory and published literature, we made a priori predictions about the factors associated with the probability of breeding dispersal and breeding dispersal distance, and about the consequences of dispersal. Breeding dispersal probability was higher for younger owls, single owls, paired owls that lost their mates, owls at lower quality sites, and owls that failed to reproduce in the year preceding dispersal. Sex had little effect on the probability of breeding dispersal. Dispersal distance was similar for female and male owls (median = 7 km, range = 1–33 km). We found no strong relationships between dispersal distance and any of the conditions that were associated with the probability of breeding dispersal. Dispersal resulted in improved territory quality in 72% of cases. These results indicate that breeding dispersal was condition-dependent and adaptive.

Population Dynamics of the California Spotted Owl (Strix occidentalis occidentalis): A Meta-Analysis

2004 ◽  
pp. 1-54 ◽  
Author(s):  
Alan B. Franklin ◽  
R. J. Gutiérrez ◽  
James D. Nichols ◽  
Mark E. Seamans ◽  
Gary C. White ◽  
...  
Keyword(s):  
Population Dynamics ◽  
Meta Analysis ◽  
Spotted Owl ◽  
Strix Occidentalis ◽  
California Spotted Owl

scholarly journals Distribution and Abundance of Spotted Owls in Zion National Park

1989 ◽  
Vol 13 ◽  
pp. 226-233
Author(s):  
R. Gutierrez ◽  
Douglas Call ◽  
Sarah Rinkevich
Keyword(s):  
National Park ◽  
Spotted Owl ◽  
Brood Rearing ◽  
Strix Occidentalis ◽  
Nest Sites ◽  
Zion National Park ◽  
Spotted Owls ◽  
Fledgling Success ◽  
Strix Occidentalis Lucida ◽  
Mexican Spotted Owls

The main objective of this study is to estimate the distribution, habitat use, and reproductive status of Mexican spotted owls (Strix occidentalis lucida) in Zion National Park. This information will allow managers to coordinate park activities that potentially conflict with nest sites, roost sites, or brood rearing habitats. Other objectives of this study are to estimate spotted owl food habits and fledgling success, and to compare these findings with other North American spotted owl populations.

Survival estimates for the northern spotted owl

1998 ◽  
Vol 28 (11) ◽  
pp. 1681-1685 ◽  
Author(s):  
Paul C Van Deusen ◽  
Larry L Irwin ◽  
Tracy L Fleming
Keyword(s):  
Survival Rates ◽  
Field Studies ◽  
Washington State ◽  
Time Span ◽  
Spotted Owl ◽  
Strix Occidentalis ◽  
Adult Females ◽  
Northern Spotted Owl ◽  
Strix Occidentalis Caurina ◽  
Capture Recapture

An analysis of capture-recapture data is tailored to the biological characteristics of the female northern spotted owl (Strix occidentalis caurina) by conditioning female capture on capture of paired males. This procedure is relevant for animals such as the northern spotted owl where field studies indicate that capture of females generally is dependent on capture of their mates. Application of the method to data collected in Washington State suggests that survival rates for adult females have remained constant over the time span of our data, 1990-1997.

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