Maturation and reproduction of northern flying squirrels in Pacific Northwest forests.

Abstract

Northern flying squirrels are the primary prey of northern spotted owls and are important dispersers of fungal spores in Pacific Northwest forests. Despite the importance of these squirrels in forest ecosystems, information is lacking on life history and methods for determining age and reproductive condition. In the laboratory, we measured epiphyseal notch, femur length, rostrum length, least interorbital breadth, rump pelage length and color, and tail width of dead squirrels. We analyzed weight, pelage color, and reproduction for field-collected data from live squirrels. We also described age-class differences in facial features and tail size and shape in the Puget Trough. A birth-year-based age-class system had several advantages over the traditional juvenile-subadult-adult class system. Three age classes can be distinguished in the field, each with varying degrees of accuracy. Reproduction of northern flying squirrels can be reliably determined in live-trapping studies. Enlargement, turgidity, and redness of genitalia are detectable signs of reproductive activity, whereas reduction, flaccidity, and paleness signal inactivity for both males and females. Nipple length is the best indicator for distinguishing sexual maturity of inactive females. The most effective way to avoid mistakes and ambiguity about age and reproductive status in the field is to take descriptive notes. Maturation and reproductive patterns were similar among the Puget Trough, Olympic Peninsula, and northern Cascade studies in Washington. Squirrels in the Coast Range of Oregon, however, displayed different patterns. Regional populations differed in proportion of females reproductively active, the reproductive maturity of yearling females, and survivorship across age classes. Regional variations suggest accurate assessment of age and reproduction is a prerequisite for understanding flying squirrel ecology.Keywords: Northern flying squirrel, maturation, reproductive biology, Oregon, Washington, live-trapping, necropsy. AbstractThere has been substantial research on old-growth Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) forests and wildlife that depend on them (Ruggiero and others 1991). Northern flying squirrels (Glaucomys sabrinus [Shaw 1801]) have been of particular interest because they seem to be keystone species in late-seral forests-a main prey of strigids and mustelids on one trophic level, and a consumer and disseminator of fungal spores on another. Through its mission to develop forest management practices that steward biodiversity, the Ecological Foundations of Biodiversity Research Team has focused research on the relation between northern flying squirrels and forest health.Despite the importance of northern flying squirrels in Pacific Northwest forest ecosystems, information is lacking on life history and methods for determining age and reproductive condition. We began studying flying squirrel populations in 1985 in Douglas-fir forests of the Coast Ranges physiographic province in southwestern Oregon (Franklin and Dyrness 19...

Maintaining wildlife habitat in southeastern Alaska: implications of new knowledge for forest management and research

“…However, summer survivorship and density of reproductive females were higher in old growth than in mixed-conifer forests (Smith and Nichols, 2003). Juvenile weights averaged 119 g on Prince of Wales Island, which is 20-40% higher than means reported for Oregon and Washington (Villa et al, 1999). Mean adult weights during spring (129 g) and autumn (123 g) (Smith and Nichols, 2003), however, seem to fall within the range of variation reported from Oregon and Washington for squirrels of similar age (Villa et al, 1999).…”

“…Juvenile weights averaged 119 g on Prince of Wales Island, which is 20-40% higher than means reported for Oregon and Washington (Villa et al, 1999). Mean adult weights during spring (129 g) and autumn (123 g) (Smith and Nichols, 2003), however, seem to fall within the range of variation reported from Oregon and Washington for squirrels of similar age (Villa et al, 1999). Juvenile recruitment into the fall population was lower on Prince of Wales Island than in the Pacific Northwest (Villa et al, 1999), which may have been related to density-dependent influences on natality or survival on Prince of Wales (Smith and Nichols, 2003).…”

Evolutionary diversity and ecology of endemic small mammals of southeastern Alaska with implications for land management planning

“…The only exception was that sex ratios consistently favored males, with a larger bias in peatland-scrub/mixed-conifer than western hemlock-Sitka spruce forests (Smith and Nichols, 2003). This pattern contrasted with slightly femalebiased sex ratios elsewhere in the Pacific Northwest (Carey, 1995;Villa et al, 1999). Also, juvenile recruitment was substantially lower in southeastern Alaska than elsewhere in the Pacific Northwest (Smith and Nichols, 2003), which may have been related to density-dependent influences on natality or survivorship (Villa et al, 1999).…”

“…This pattern contrasted with slightly femalebiased sex ratios elsewhere in the Pacific Northwest (Carey, 1995;Villa et al, 1999). Also, juvenile recruitment was substantially lower in southeastern Alaska than elsewhere in the Pacific Northwest (Smith and Nichols, 2003), which may have been related to density-dependent influences on natality or survivorship (Villa et al, 1999). Summer survivorship of flying squirrels in southeastern Alaska was higher in western hemlock-Sitka spruce forests than in peatlandscrub/mixed-conifer, whereas overwinter survival and longevity were similar between habitats (Smith and Nichols, 2003).…”

Forest Structure Within Barred Owl (Strix varia) Home Ranges in the Eastern Cascade Range, Washington

“…Fungal species differ in the moisture, temperature and nutrients gained from the mineral soil and organic matter (Molina and Trappe 1982, Molina et al 1992, Carey et al 1999a. "Fungal production drops in summer with drought…" (Franklin and Dyrness 1973, USDC National Oceanic and Atmospheric Association 1981, Villa et al 1999. "Lichen litterfall biomass increased with increasing stand complexity and moisture" (Lehmkuhl 2004:381).…”