may use younger forests for foraging than air max

Wysłany: Sob 19:38, 19 Mar 2011

Although similar to nesting and roosting habitat requirements, foraging habitat requirements are likely less strict. Like nesting and roosting sites,[link widoczny dla zalogowanych] foraging areas are generally older [24][51][58], have higher canopy covers [45][59], greater tree densities [27][45][59], and more snags and coarse woody debris [13][27][45] than random sites. In the Coast Ranges of southern Oregon, northern spotted owls foraged in forests older than expected [58]. In northwestern California, foraging sites were older than sites that were infrequently used [51]. However, California [45] and northern [13] spotted owls may use younger forests for foraging than for nesting or roosting. For instance, stands as young as 27 years old were used by foraging northern spotted owls in coniferous forests of the western Cascade Range in Oregon[13]. Although Mexican spotted owls foraged in old stands and stands with more than 60% canopy cover in ponderosa pine-Gambel oak forests in Arizona, canopy cover on foraging sites was lower than on roosting sites [24]. California spotted owls did not select areas with greater canopy cover at the patch scale (≥5 acres, 2 ha) as consistently for foraging as they did for roosting in the Sierra Nevada [60].[link widoczny dla zalogowanych] Log volume and snag basal area and density were similar on foraging and roosting sites on sites in Arizona and New Mexico, but stands with less than 60 ft2/acre basal area, less than 25% canopy cover, and very high Gambel oak densities were used for foraging and not for breeding-season roosts [29]. Mexican spotted owl foraging sites also differed from roosting sites in study areas near Flagstaff and Alpine, Arizona, with large coarse woody debris, density of snags, tree density, and canopy cover significantly (P<0.001) higher on roosting sites [61]. Some sources suggest that foraging habitat has more open area under the canopy to allow for spotted owl flight [66]. Increased habitat heterogeneity may also be important to foraging spotted owls by providing more varied prey.[54]
Predominant prey is likely to contribute to differences in spotted owl habitat selection across their range, since spotted owl prey species occur in a variety of habitats. For instance,[link widoczny dla zalogowanych], in coniferous forests of southwestern Oregon and the Olympic Peninsula in Washington, flying squirrel densities in old-growth forests were typically about twice those in younger stands [10], while dusky-footed woodrats (Neotoma fuscipes) in northwestern California tend to occur in early-successional shrublands.[67] Young forest stands did not positively affect California spotted owl reproduction or site occupancy in a white fir-mixed-conifer study area on the Lassen National Forest [41]. Northern flying squirrel was the major prey item in this area.[link widoczny dla zalogowanych] In contrast, in areas where dusky-footed woodrats are a substantial component of the diet, such as in some areas of northwestern California [54][68], some interspersion of younger or more open stands with mature and old-growth forests is likely beneficial