DENS OF NORTHERN FLYING SQUIRRELS IN THE PACIFIC-NORTHWEST

Silvicultural prescriptions to enhance northern flying squirrel (Glauc omys sabrinus) habitat have been suggested as an aid for recovery of t he threatened northern spotted owl (Strix occidentalis caurina). Flyin g squirrels are hypothesized to be limited by den sites (cavities in t rees) and by food (truffles). However, no quantitative information exi sts on den sites of flying squirrels. Therefore, during 1986-94, we us ed radio-telemetry to locate 604 different den sites in the southern C oast Range of Oregon, the southern Olympic Peninsula, and the Puget Tr ough of Washington. Den sites included cavities in live and dead old-g rowth trees; cavities, stick nests, and moss nests in small (10-50 cm dbh) second-growth trees; dens in cavities in branches of fallen trees ; and dens in decayed stumps of old-growth trees and suppressed young trees. Two-thirds of all dens located were in live trees. Most dens we re located during a study of second-growth forests in the Puget Trough . Females selected cavities for maternal dens. Squirrels used multiple dens; denning partners varied with den. Dens of males were 211 +/- 7 m apart; dens of females were 108 +/- 4 m apart. Males used 2.2 +/- 0. 1 dens per month; females 2.3 +/- 0.1 dens per month. Dens, except mat ernal dens, were often occupied simultaneously by several adult squirr els. Many fragile den sites were used by females. Secure cavities are scarce and may limit reproductive success. Management for cavity trees and dens could prove fruitful in owl recovery and habitat restoration efforts.