Nest Site Selection by Western Gray Squirrels at Their Northern Range Terminus

Abstract

The western gray squirrel (Sciurus griseus) in Washington, USA, is limited to 3 disjunct areas and is a state threatened species.Information is lacking for the North Cascades population, which is the northernmost population for the species. Squirrels in this population exist without oaks (Quercus spp.) that provide forage and cavities for maternal nests elsewhere in their range. During May 2003 to August 2005, we studied selection of nest sites and nest trees by 18 radiocollared squirrels in Okanogan County, Washington. Without oak cavities, females reared their young in dreys. General nest-tree characteristics were similar to characteristics of western gray squirrel nest trees in Southeastern Cascades: relatively tall ponderosa pines (Pinus ponderosa) L 40 cm diameter at breast height. Results from conditional logistic models determined that the odds of a squirrel selecting a tree for nesting increased with greater diameter at breast height and with infection by dwarf mistletoe (Arceuthobium spp.). Nest sites with high selection probability by squirrels had greater basal area and number of tree species than available unselected sites. Retention of forest patches that include a mix of conifer species or conifer and deciduous trees and moderate to high basal area could promote nesting opportunities, connectivity for arboreal travel, as well as abundance and diversity of hypogeous fungi. Experiments to test the efficacy of retaining untreated patches of varying size (including trees infected with mistletoe) on nesting by western gray squirrels within stands managed for fire suppression and forest health would provide important information about the effects of forest fuel management on arboreal wildlife.

Nest site selection by the hazel dormouse Muscardinus avellanarius: is safety more important than food?

“…Connectivity of the nestbox tree with the surroundings was the best in nest sites used by M. avellanarius for breeding and preferred for resting. Nest site connectivity for arboreal travel was also a significant predictor of nest site selection by the western grey squirrel Sciurus griseus (Gregory et al 2010) and Abert's squirrel Sciurus aberti (Edelman and Koprowski 2005).…”

“…In most cases, nest site selection by mammals has been studied using comparisons of characteristics of nest sites with randomly selected sites or sites not used by the animals (e.g., Bertolino and Cordero di Montezemolo 2007;Gregory et al 2010;Cudworth and Koprowski 2011). At our study site, only 10 of the 272 nestboxes were not used at all by M. avellanarius in the period 2007 to 2011.…”

Home range and habitat selection by a threatened bat in exotic plantation forest

“…Whilst the small sample sizes of this study mean that inferences should be treated cautiously, they are typical for studies of threatened species (Sasso and Epperly, 2007;Claridge et al, 2009;Hillen et al, 2009;Gregory et al, 2010;Hwang et al, 2010) and studies with similarly small sample sizes have been used to inform management (Sasso and Epperly, 2007;Rayment et al, 2009). In addition, within plantation forests roosting structures are rare (Ciechanowski, 2005;Borkin, 2010) and population size may be more limited by roost numbers than those studied elsewhere meaning large sample sizes are difficult or impossible to obtain.…”

Differential Resource Use between Native and Introduced Gray Squirrels

“…Western gray squirrels were listed as a threatened species by the state of Washington in 1993, where habitat loss and competition with introduced squirrels are postulated reasons for population declines (Linders and Stinson 2007). Previous researchers have described habitat associations of western gray squirrels in the Cascade Mountains in some detail (Linders 2000, Gregory et al 2010, Stuart et al 2018), but only broad associations have been described for this species in western Washington (Ryan and Carey 1995, Bayrakçi et al 2001, Fimbel and Freed 2008). Most remaining habitat in western Washington for western gray squirrels occurs in areas subject to timber harvest or expanding urban development.…”

“…Western gray squirrels commonly inhabit conifer‐oak ( Quercus spp.) forests and have not been reported to have strong riparian affiliations in Washington (Linders 2000, Gregory et al 2010, Stuart et al 2018). Such habitat differences between species may be important to interspecies interactions.…”