Evaluating Desired Conditions for Mexican Spotted Owl Nesting and Roosting Habitat (original) (raw)
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Forest Science
California spotted owl (Strix occidentalis occidentalis) nest sites are associated with large trees, moderate-to-high tree densities, high canopy cover, and structural complexity. Therefore, forest managers need accurate estimates of these characteristics. Standard forest inventory metrics, such as those estimated from Forest Inventory and Analysis (FIA) data, are used by silviculturists to assess forest trends and condition, and are a source of data for assessing wildlife habitat. We estimated which FIA metrics best predicted California spotted owl nesting habitat by developing a nesting-habitat model comparing owl nest stands with randomly chosen forest stands in potential nesting habitat (stands dominated by 3060.9- and 61-cm diameter trees and 40% cover) in the central Sierra Nevada. Number of large trees (76.2 cm) and canopy cover were the best predictors of owl nesting habitat. We present a nesting-habitat selection model based on our analysis. FIA metrics may be useful for q...
Range-wide analysis of northern spotted owl nesting habitat relations
Forest Ecology and Management, 2015
Recently the US Fish and Wildlife Service, as part of a critical habitat analysis for the northern spotted owl (Strix occidentalis caurina), developed habitat suitability models based on thousands of owl nest sites distributed across 11 regions using the MaxEnt tool. Because these models formed the basis for critical habitat designations on millions of hectares of land, we undertook an independent evaluation of the FWS effort. We evaluated the accuracy of vegetation data used as input to develop the models, conducted out of sample analyses, correlated model output with owl reproductive success in two study areas, and developed alternate models using two different statistical methods. Vegetation data appeared accurate for only a few variables, and accuracy varied among model regions. Out of sample testing gave a high rate of classification errors and owl productivity was not correlated with MaxEnt model output in two study areas. Alternate statistical methods produced reasonable models with fewer variables. Critically, neither the models compared across regions nor the regions analyzed with different tools led to comparable use of variables. Thus biological interpretation of owl habitat selection models seemed ambiguous. In addition, for MaxEnt and one of the other tools, a highly significant trend by regression was found showing decreasing model accuracy as number of training nest sites increased. Together, these two results suggest that the generated models may be spurious to some unknown degree, perhaps because the underlying vegetation data, also derived from a model, are not sufficiently accurate to support the analysis and/or because the owls themselves affect habitat suitability by consuming their prey base. We suggest that the USFWS exercise caution in using MaxEnt models as a basis for regulatory purposes such as consultation, estimating likelihood of occupancy by owls, or evaluation of site-specific recovery actions.
Nesting habitat of Mexican spotted owls in the Sacramento Mountains, New Mexico
The Journal of Wildlife Management, 2013
Understanding the habitat relationships of rare species is critical to conserving populations and habitats of those species. Nesting habitat is suspected to limit distribution of the threatened Mexican spotted owl (Strix occidentalis lucida), and may vary among geographic regions. We studied selection of nesting habitat by Mexican spotted owls within their home ranges in the Sacramento Mountains, New Mexico. We compared characteristics of owl nest trees and nest sites to characteristics of randomly located trees and sites at 2 spatial scales: the general nest vicinity and within activity centers used by spotted owls. Owls nested primarily in mixed-conifer forest (92%), and most nested in cavities in trees or snags (48%), or in dwarf mistletoe (Arceuthobium spp.) witches' brooms (36%). Owl nest trees had greater levels of dwarf mistletoe infection and were larger in diameter than random trees at both of the evaluated spatial scales. Nest trees also were more likely than random trees to be in white fir (Abies concolor) or Douglas-fir (Pseudotsuga menziesii), and in trees or snags with broken tops. Differences between owl nest sites and random sites differed with the scale at which we selected random sites, but at both scales examined, owl nest sites had greater canopy cover and more basal area contributed by large trees and white fir than random sites. In addition, most nest sites occurred in drainage bottoms or on the lower 2 thirds of north-or east-facing slopes. Conservation of owl nesting habitat in this area will require retaining forest patches with high canopy cover and large trees containing cavities or large dwarf mistletoe witches' brooms. Locating forest management treatments on ridgetops or the upper third of slopes and/or on south-or west-facing slopes may reduce impacts to owl nesting habitat while simultaneously targeting the drier forest types most in need of restoration. Ó 2013 The Wildlife Society.
Canopy Closure around Nest Sites of Mexican Spotted Owls in Northcentral Arizona
The Journal of Wildlife Management, 1997
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. . Wiley and Wildlife Society are collaborating with JSTOR to digitize, preserve and extend access to The Journal of Wildlife Management. Abstract: We analyzed variation in canopy closure around 47 Mexican spotted owl (Strix occidentalis lucida) nest sites and 47 random forest sites on the Coconino National Forest in northcentral Arizona. We mapped distinct habitat polygons on 1:15,840 color aerial photographs, assigned each polygon to one of 4 canopy-closure classes (<10, 10-40, 41-70, or >70%), and measured the area in each canopy class within 5 concentric analysis zones with radii of . Landscape composition differed between spotted owl nest and random sites (P < 0.001). Differences were greatest within 0.4 km of nest and random sites but persisted across all analyses zones. Nest sites contained more area in the >70% canopy-closure class and less area in the < 10% class. The most abundant canopy class was 41-70%, except within 0.1 km of nests, where >70% canopy predominated. Nesting spotted owls selected areas with denser canopy than randomly available forest landscapes, but outside the immediate nest area (>0.8 km) canopy closure approached that of the surrounding forest.
The Journal of wildlife …, 2005
The California spotted owl (Strix occidentalis occidentalis) has been at the center of political and administrative debate due to its association with commercially valuable forest. Several studies have compared the forest cover types used by California spotted owls with the cover types that are generally available, establishing the association between spotted owls and old/large tree components of forests at the landscape scale. We sought a deeper understanding of spotted owl habitat associations in areas in which owls had already selected territories. We mapped and classified vegetation within circular plots (radius 2.4 km) around 67 spotted owl sites in northeastern California, USA. We evaluated the relationships between habitat composition within the different owl sites and variation in (1) nest success (1990-2000) and (2) site occupancy, apparent survival probability, and reproductive output (1993-1998). All analyses included data representing 2 spatial scales: core area (814 ha) and nest area (203 ha). Site occupancy was positively associated with the amount of the nest area dominated by large trees with high canopy cover within the nest area. It was negatively associated with the amount of nonhabitat (nonforested areas and forest cover types not used for nesting or foraging) and with medium-sized trees with high canopy cover. Site occupancy also decreased with time and elevation. Apparent survival probability varied annually and was positively related to the area of each habitat class multiplied by the quotient proportion used/proportion available for each type, at both the nest and core scales. Reproductive output was negatively related to elevation and nonhabitat within the nest area. Nest success was positively associated with the presence of large remnant trees within the nest stand.
Landscape and Urban Planning, 2009
At the southern end of its range, the Northern Spotted Owl (Strix occidentalis caurina) occurs in high densities and nests in a wide range of forest types and ages, exhibiting different foraging and nesting habits than in the northern part of its range. The intensive monitoring of this subspecies on public lands in Marin County, California, combined with the availability of fine-scale geographic information system (GIS) data, provided a unique opportunity to apply and evaluate a habitat-based species occurrence modeling approach at the scale most relevant to local land managers and planning agencies. We used 4 years of breeding owl survey data (1998)(1999)(2000)(2001) and GIS layers representing topographic, anthropogenic, and vegetation-based landscape characteristics to build logistic regression models of owl nest-site occurrence. Models were used to develop spatial predictions of occurrence within the study area and in adjacent ecoregions, which were validated with an independent dataset. We also compared the predictive performance of two vegetation layers differing in their floristic detail and spatial accuracy. The model based on a local vegetation layer generally exhibited better model performance than the model based on the more generic regional layer. Model results indicated that forest connectivity and topographic conditions, rather than forest type or age, were the strongest predictors of nesting owl presence. Predicting outside the original study area was somewhat successful for a coastal ecoregion similar in vegetation and climate, but not better than random for a nearby inland ecoregion, suggesting that locally derived models are necessary to adequately predict nest-site occurrence.
Old-forest distribution around spotted owl nests in central cascade mountains
1999
Unlike previous spotted owl (Strix occidentalis) habitat association studies, we restricted our inquiry to the old-forest type and thus explored the association of spotted owls with habitat distribution as opposed to habitat type. We compared old-forest distribution around 126 northern spotted owl (S. o. caurina) nests in 70 pair territories, 14 nonreproductive spotted owl activity centers, and 104 points drawn randomly from old forest (closed canopy, >80 yr) in the central Cascade Mountains of Oregon. We quantified the percentage of old forest within 50 concentric circular plots (0.1-5.0-km radii) centered on each analyzed point, and we used logistic regression to make spatially explicit inferences. Owl nests were surrounded by more old forest in plots with 0.2-0.8-km radii (P < 0.05). Results suggested the landscape scales most pertinent to northern spotted owl nest-site positioning in this study were (in descending order) (1) the surrounding 15 ha (approx 200-m radius), (2) the surrounding 30-115 ha (approx 300-600-m radius), (3) the surrounding 200 ha (800-m radius), and (4) possibly the surrounding 700 ha (1,500-m radius). Nests were associated with higher proportions of old forest near the nest, implying that the arrangement of habitat was important for nest-site selection, positioning, or both. The 70 territories of nesting owls had more old forest on average than did the 14 nonreprodu•tive owl sites, and the probability that a pair nested at least once during the study was positively associated with area of old-forest habitat in all radii studied. Because spotted owls in the central Cascade Mountains of Oregon are known to have home ranges that average 1,769 ha, our results apply to nest-site location on the landscape and not to the amount of habitat necessary for pair persistence or successful reproduction.
Cover of tall trees best predicts California spotted owl habitat
Forest Ecology and Management, 2017
Restoration of western dry forests in the USA often focuses on reducing fuel loads. In the range of the spotted owl, these treatments may reduce canopy cover and tree density, which could reduce preferred habitat conditions for the owl and other sensitive species. In particular, high canopy cover (≥70%) has been widely reported to be an important feature of spotted owl habitat, but averages of stand-level forest cover do not provide important information on foliage height and gap structure. To provide better quantification of canopy structure, we used airborne LiDAR imagery to identify canopy cover in different height strata and the size and frequency of gaps that were associated with owl nest sites, protected activity centers (PACs), and territories within four study areas and 316 owl territories. Although total canopy cover was high in nest stands and PAC areas, the cover in tall (> 48 m) trees was the canopy structure most highly selected for, while cover in lower strata (2-16 m) was avoided compared to availability in the surrounding landscape. Tall tree cover gradually decreased and lower strata cover increased as distance increased from the nest. Large (> 1000 m 2) gaps were not found near nests, but otherwise there was no difference in gap frequencies and sizes between PACs and territories and the surrounding landscape. Using cluster analysis we classified canopy conditions into 5 structural classes and 4 levels of canopy cover to assess the relationship between total canopy cover and tree size within nest sites, PACs, and territories. High canopy cover (≥70%) mostly occurs when large tree cover is high, indicating the two variables are often confounded. Our results suggest that the cover of tall trees may be a better predictor of owl habitat than total canopy cover because the latter can include cover in the 2-16 m strataconditions that owls actually avoid. Management strategies designed to preserve and facilitate the growth of tall trees while reducing the cover and density of understory trees may improve forest resilience to drought and wildfire while also maintaining or promoting the characteristics of owl habitat.
Old-Forest Distribution around Spotted Owl Nests in the Central Cascade Mountains, Oregon
Journal of Wildlife Management, 1999
Unlike previous spotted owl (Strix occidentalis) habitat association studies, we restricted our inquiry to the old-forest type and thus explored the association of spotted owls with habitat distribution as opposed to habitat type. We compared old-forest distribution around 126 northern spotted owl (S. o. caurina) nests in 70 pair territories, 14 nonreproductive spotted owl activity centers, and 104 points drawn randomly from old forest (closed canopy, >80 yr) in the central Cascade Mountains of Oregon. We quantified the percentage of old forest within 50 concentric circular plots (0.1-5.0-km radii) centered on each analyzed point, and we used logistic regression to make spatially explicit inferences. Owl nests were surrounded by more old forest in plots with 0.2-0.8-km radii (P < 0.05). Results suggested the landscape scales most pertinent to northern spotted owl nest-site positioning in this study were (in descending order) (1) the surrounding 15 ha (approx 200-m radius), (2) the surrounding 30-115 ha (approx 300-600-m radius), (3) the surrounding 200 ha (800-m radius), and (4) possibly the surrounding 700 ha (1,500-m radius). Nests were associated with higher proportions of old forest near the nest, implying that the arrangement of habitat was important for nest-site selection, positioning, or both. The 70 territories of nesting owls had more old forest on average than did the 14 nonreprodu•tive owl sites, and the probability that a pair nested at least once during the study was positively associated with area of old-forest habitat in all radii studied. Because spotted owls in the central Cascade Mountains of Oregon are known to have home ranges that average 1,769 ha, our results apply to nest-site location on the landscape and not to the amount of habitat necessary for pair persistence or successful reproduction.
Landscape Ecology, 1998
Investigations using available data sought to guide short-term management decisions regarding the needs of northern spotted owl in the high Cascade Mountains of Oregon. Landscape attributes and pattern indices were measured and tested for identification of areas likely to contain northern spotted owl nests. Predictive models indicating planning standards were developed. Most landscape ecological indices were not useful. Results indicate the owl favors landscapes dominated by patches that meet definitions of late seral forest nesting habitat. The owl optimally nests in such patches at least 570 hectares in size. Landscapes with some edges, particularly around nesting habitat patches evidently do not adversely affect the owl, perhaps because they provide prey. Landscapes with extensive edges, particularly between openings and forests not suitable for nesting, are not as likely to be selected. The results are largely consistent with the owl's recovery plans, provide guidance for management, and require refinement through additional research, particularly to better determine home range sizes.