Nest trees of northern flying squirrels in the Sierra Nevada

We examined the nest-tree preferences of northern flying squirrels (Glaucomys sabrinus) in an old-growth,\ud mixed-conifer and red fir (Abies magnifica) forest of the southern Sierra Nevada of California. We tracked 27\ud individuals to 122 nest trees during 3 summers. Flying squirrels selected nest trees that were larger in diameter\ud and taller than either random trees or large (.50-cm diameter at breast height) nearest-neighbor trees. Snags were\ud used more often than live trees relative to their availability. Nest trees were usually close to riparian habitat; 86%\ud of nest trees were ,150 m from a perennial creek. Flying squirrels selected red fir and avoided incense cedar\ud (Calocedrus decurrens). Mean distances between nest trees and size of core-nest areas were greater for males\ud than for females. No detectable relationship was found between size of core-nest area and distance to a perennial\ud creek. These results suggest that flying squirrels of the Sierra Nevada may require large trees and snags within\ud 150 m of perennial creeks for their critical habitat needs