Observations of Boreal Toads (Bufo boreas boreas) and Batrachochytrium dendeobatidis in SOuth Central Wyoming and North-Central Colorado

摘要

Boreal Toads (Bufo horeas boreas) are found throughout much of the western United States, and were historically viewed as common. Presently, this taxon is considered a species of concern in some western states (Maxell et al. 2003; McGee et al. 2002) and populations in the southern Rocky Mountains have decreased to the extent that they have been considered for listing under the Endangered Species Act (U.S. Fish and Wildlife Service 2005). Although a causal link has not been established, rapid declines in Boreal Toad populations have been associated with the presence of the chytrid fungus Batrachochytrium dendrobatidis (hereafter Bd) in northern Colorado (Muths et al. 2003; Scherer et al. 2005) and Bd has been implicated in the mass mortality of several other species of amphibians (Quellett et al. 2005; Rachowicz et al. 2006).Accurately monitoring trends in Boreal Toad abundance and distribution is difficult partly because population surveys often rely on qualitative observations at or near breeding areas (Loeffler 2001). Temporal variation in habitat availability (Bartelt et al. 2004), explosive breeding behavior (Olson et al. 1986), periodic recruitment failures (Olson 1992), high turnover in the use of breeding areas (Trenham et al. 2003), and difficulty in detecting breeding assemblages (Hammerson 1999) may lead to substantial fluctuations in actual and perceived toad abundance (Corn et al. 2005; Heyer et al. 1994; Wente et al. 2005). Consequently, alternative methods for detecting the presence and relative abundance of Boreal Toads would be useful. Recently, researchers in Montana studying the summer movements of stream fishes coincidentally captured large numbers of downstream-drifting Boreal Toads in hoop nets (Adams et al. 2005). Subsequent netting directed at assessing in-stream movements by Boreal Toads detected them in many previously unsampled basins (M. Young and D. Schmetterling, unpubl. data). If use of streams by Boreal Toads is geographically widespread and temporally consistent, the installation of upstream-facing hoop nets may increase the options for sampling toad populations (cf. Hcyer et al. 1994; Willson and Dorcas 2004).