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Use of Fungal Rhizomorphs as Nesting Material by Glaucomys volans (Southern Flying Squirrels)
Suzanne Prange and David H. Nelson

Southeastern Naturalist, Volume 5, Number 2 (2006): 355–360

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2006 SOUTHEASTERN NATURALIST 5(2):355–360 Use of Fungal Rhizomorphs as Nesting Material by Glaucomys volans (Southern Flying Squirrels) Suzanne Prange1,2,* and David H. Nelson1 Abstract - We examined 53 nests of southern flying squirrels constructed within nest boxes in Mobile County, AL. Of those containing a bedding layer (n = 35), 80% contained fungal rhizomorphs of Marasmius brevipes. Rhizomorphs of this genus have been reported in bird-nest descriptions, but have not been documented in flying squirrel nests. M. brevipes was common on our study site, and its use by flying squirrels may be unique to the area. Nevertheless, this and similar species of rhizomorph-producing fungi occur in other portions of the flying squirrel’s range, and the nondescript nature of rhizomorphs may lead to their misidentification. Our observations appear to constitute the first description of an ecological relationship between this fungus and a mammalian species. Introduction Glaucomys volans (L.) (southern flying squirrels) are largely a cavitynesting species, although outside nests have been reported (Dolan and Carter 1977, Ivey 1959, Landwer 1935, Moore 1947, Snyder 1921). Nests in cavities or nest boxes, particularly those used during summer, may consist of only a thin layer of leaves or mosses (Gilmore and Gates 1985, Muul 1968). Nests used during cooler periods and those constructed by pregnant or lactating females, however, are often designed more elaborately and typically include a layer of soft bedding material on top or within a layer of leaves and/or mosses (Gilmore and Gates 1985; Muul 1968, 1974; Sonenshine et al. 1979). Material in the bedding layer is usually woven into a chamber in the form of either a cup-like structure or an enclosed ball. This layer is most often composed of finely shredded inner bark (Gilmore and Gates 1985; Goertz et al. 1975; Heidt 1977; Jackson 1961; Layne 1958; Muul 1968, 1974; Sollberger 1943), although Tillandsia usneoides (L.) L. (Spanish moss) was most commonly used in Florida (Ivey 1959, Moore 1947). Outside nests are typically constructed externally of leaves and twigs, and frequently contain a bedding layer of shredded bark (Ivey 1959, Landwer 1935, Snyder 1921). As in cavity nests, however, Moore (1947) reported the extensive use of Serenoa repens (Bartr.) Small (palmetto) and Spanish moss in outside nests in Florida, with nests occasionally constructed within fresh streamers of the latter. Other nesting materials have been reported in both cavity and outside nests, including: hair, wool, feathers, 1Department of Biological Sciences, University of South Alabama, LSB 124, Mobile, AL 36688. 2Current address - Max McGraw Wildlife Foundation, PO Box 9, Dundee, IL 60118. * Corresponding author - 356 Southeastern Naturalist Vol. 5, No. 2 lichens, grass, pine straw, and chips of outer bark (Dolan and Carter 1977, Goertz et al. 1975, Heidt 1977, MacClintock 1970, Muul 1974). Glaucomys sabrinus (Shaw) (northern flying squirrels) also utilize both outside and cavity nests, and nest construction is similar to that of G. volans (Jackson 1961, Wells-Gosling and Heaney 1984). From the few available descriptions of nests in cavities or nest boxes, however, it appears the primary bedding material varies by location. In British Columbia, Cowan (1936) described a hollow tree containing the remains of 14 nests that consisted primarily of shredded bark, and Harestad (1990) similarly reported shredded bark as the primary material in nest boxes, although the use of moss was also observed. Ten cavity nests examined in the Pacific Northwest (Oregon and Washington), however, were all lined with moss, and moss constituted > 90% of the material in nest boxes (Carey et al. 1997). In central Idaho and western Montana, cavity nests were constructed almost entirely of arboreal lichens (Hayward and Rosentreter 1994). Likewise, some descriptions of outside nests have noted bedding layers of shredded bark (Cowan 1936, Manville 1942, Weigl and Osgood 1974), whereas others have reported the primary constituent of the bedding layer to be moss (Carey et al. 1997) or lichens (Rust 1946). Other materials found in both cavity and outside nests of G. sabrinus have included: wool, grass, conifer needles, polyester batting (stolen from live-traps, where it was used to provide insulation), paper, fern fronds, beargrass, feathers, and egg-shell fragments (Bailey 1929, Carey et al. 1997, Cowan 1936, Hayward and Rosentreter 1994). Use of fungal rhizomorphs of the genus Marasmius has been reported for bird nests (Foster 1976, Hedger 1990, McFarland and Rimmer 1996, Pérez- Rivera 1993, Young and Zuchowski 2003). McFarland and Rimmer (1996) examined 54 nests of 10 species of birds in a subalpine spruce-fir community in the northeastern United States and found 85% of the nests contained rhizomorphs of M. androsaceus (L. ex Fr.) Fr. Interestingly, this was the first reported use of marasmioid rhizomorphs as a nesting material by birds in North America. The authors, however, speculated that previous descriptions of nesting material as “black roots,” “rootlets,” “moss stems,” or “hair” may have actually described rhizomorphs. Although its use by birds is now well documented, use of marasmioid rhizomorphs has not been reported for flying squirrels or, to the best of our knowledge, any other small mammal. In this paper, we describe the use of fungal rhizomorphs as nesting material by southern flying squirrels. Methods During a larger study examining habitat use by southern flying squirrels (Hatten 1992), we deployed 100 nest boxes (internal dimensions: 15 x 15 x 30 cm) similar to those of Sonenshine et al. (1973). Our study site was a 6-ha oakpine woodland within a suburban park (Cottage Hill Park) in Mobile County, AL. The canopy was comprised primarily of Pinus palustris Mill. (longleaf 2006 S. Prange and D.H. Nelson 357 pine), Quercus hemisphaerica Bartr. ex Willd. (laurel oak), Q. virginiana Mill. (live oak), P. taeda L. (loblolly pine), and Q. falcata Michx. (southern red oak). We used a grid system with 25-m intervals and hung nest boxes at 3– 4 m height on the tree nearest each grid point. We checked nest boxes for occupancy every 2 weeks from June 1991 through May 1992 and made detailed observations on the construction of nests when present. Results and Discussion Overall, 53 nest boxes contained southern flying squirrel nests. In general, nest construction was similar to that previously reported (Gilmore and Gates 1985; Goertz et al. 1975; Heidt 1977; Muul 1968, 1974; Sollberger 1943). Eighteen nests (34%) consisted solely of leaves and/or pine straw, whereas 35 (66%) contained an additional bedding layer. As in previous nest descriptions, shredded inner bark was a major constituent of the bedding layer, occurring in 33 (94%) of these nests. Most of these nests (n = 28, 80%), however, also contained numerous black, hair-like fibers interwoven with the bark shavings. The incorporation of these fibers appeared to add stability to the bedding chamber. Furthermore, in 2 cases the bedding layer consisted exclusively of this material woven into a cup-like structure. Upon closer examination, minute fruitbodies were observed growing directly from the black hair-like fibers. Mycologist Juan Luis Mata (University of South Alabama; Mobile, AL) identified these fibers as rhizomorphs of Marasmius brevipes (Berkeley and Ravenel in Berkeley and Curtis). This species and several other members of the genus Marasmius are saprotrophic or parasitic on tree branches, deciduous leaves, and conifer needles (Desjardin and Petersen 1989, Gilliam 1976). A subset of these species are often referred to as “horsehair fungi” and are characterized by copious production of thin, wiry rhizomorphs, which allow for the colonization of leaves and branches (Seaver 1944). Marasmius brevipes occurs throughout the southeastern United States (Desjardin and Petersen 1989) and was abundant on our study site on decaying wood and leaves, as well as on branches and leaves of living trees. Although this species has been previously documented in Alabama (one record in Monroe County, near Uriah; Desjardin and Petersen 1989), this appears to be the first record of its occurrence in Mobile County, located approximately 100 km southwest of Uriah, AL. Southern flying squirrels are highly adaptable and opportunistic in their choice of nesting material (Muul 1974). Flying squirrels at our suburban study site also made use of anthropogenic items, including synthetic fibers similar to upholstery stuffing (n = 18 nests, 34%; the source of this material was never located), shredded newspaper (n = 1, 2%), plastic bags (n = 1, 2%), and candy wrappers (n = 1, 2%). As noted by Muul (1974), choice of nesting materials by G. volans appears to reflect what is locally available. Species of Marasmius, as well as Marasmiellus (which also contains rhizomorph-producing species), occur widely within the southern flying 358 Southeastern Naturalist Vol. 5, No. 2 squirrel’s range. Therefore, it is possible fungal rhizomorphs in nests of flying squirrels have been overlooked or misidentified in previous descriptions, as appears to be the case for a number of bird species in North America. Very little is known about M. brevipes, and the few studies reporting on this species were limited to taxonomic and anatomical issues (Desjardin and Petersen 1989). To our knowledge, no study has dealt with their ecology or their ecological relationships within natural communities (J.L. Mata, pers. comm.). As such, our observation of M. brevipes use by southern flying squirrels not only documents extensive use of a previously unreported nesting material, but also provides the first description of an ecological relationship between this fungus and a mammalian species. Several species of Marasmius produce antibiotic agents (Melin et al. 1947), as do many species of lichens (Huneck 1999, Muller 2001), which are a common component of flying squirrel nests (Dolan and Carter 1977, Hayward and Rosentreter 1994). Thus, the incorporation of rhizomorphs of Marasmius into nests might protect against pathogens and parasites (McFarland and Rimmer 1996); however, this remains unconfirmed. Use of M. brevipes by southern flying squirrels raises further questions regarding potential ecological relationships. For example, northern flying squirrels commonly incorporate lichens in their nests, which serve not only as structural material, but also as food (Cotton and Parker 2000, Cowan 1936). Thus, G. sabrinus may function as an important dispersal agent for certain lichens (Hayward and Rosentreter 1994). We do not know if southern flying squirrels consume M. brevipes, or whether collection and transport of rhizomorphs to nests facilitate dispersal of this fungus. Additional research is needed to determine to what extent southern flying squirrels use marasmioid rhizomorphs, and to explore potential ecological relationships between flying squirrels and M. brevipes, as well as other rhizomorph-producing species. Regardless of any broader ecological relationship, fungal rhizomorphs appear to provide an abundant, easily manipulated, and structurally stable nesting material for southern flying squirrels. Acknowledgments We are grateful to the Mobile Parks Department for access to Cottage Hill Park. We are likewise grateful to the Environmental Studies Center for use of their facilities. We thank the following individuals who assisted with fieldwork: D. Biggs, T. Legarduer, and L. White-Buchanan. Helpful criticisms were received from two anonymous reviewers and guest editor, Thomas J. Maier. Finally, we are grateful to Dr. Juan Luis Mata for identifying our fungal specimens and providing us with additional information on rhizomorph-forming fungi. 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