Density of Fishers in Boreal Mixed-Wood Forests of Northeastern British Columbia

Big, sick, and rotting: Why tree size, damage, and decay are important to fisher reproductive habitat

“…However, unlike other cavity-users such as woodpeckers, fishers are not primary cavity excavators; they may require decay to be significantly progressed beyond that achieved by fungi and may need additional physical breakdown of the dead interior wood by arthropods (e.g., Hammond et al, 2003) for a suitable cavity to form. The features of balsam poplar trees used by fishers as dens in our study were similar to those found in black cottonwood trees elsewhere in British Columbia, where the majority of dens occurred in cavities accessed through branch-hole infection courts (Weir and Harestad, 2003;Weir and Corbould, 2008). Unlike southern portions of their range where activities of primary cavity excavators are important sources of inoculation and cavities used by fishers (Raley et al, in press), fishers in the boreal forest used entrances and cavities that showed very little or no evidence of excavation by other vertebrates.…”

“…We captured, radiotagged, and radiolocated fishers throughout our study area between 2005(Weir et al, 2011. All capture, handling, and radiotagging protocols met or exceeded capture and handling guidelines outlined in the protocols for Wildlife Capture and Handling (Resource Inventory Committee, 1998) and were carried out under Wildlife Act permit FSJ05-9483.…”

“…In British Columbia, female fishers care for their young exclusively in cavities in trees (Lofroth et al, 2010) that they use continuously for periods of up to 3 months after giving birth. Fishers will occasionally use up to three different den trees during the rearing period between April and June (Paragi et al, 1996;Weir and Corbould, 2008).…”

“…This damage must be of particular dimensions to also provide predator-secure access for the female to the interior of the tree, typically through frost cracks, fire-scars, large anchored branches pulling out from the tree bole, and woodpecker holes (Lofroth et al, 2010). With a body mass between 2 and 3.5 kg and overall length approaching 1 m, female fishers are among the largest obligate-tree cavity users in North America and trees used as dens need to be large enough to provide a cavity that has an inside diameter of >30 cm (Weir and Corbould, 2008).…”

“…In the sub-boreal forests of central British Columbia, reproductive dens are most frequently found in large-diameter black cottonwood (Populus balsamifera spp. trichocarpa) trees (Weir and Harestad, 2003;Weir and Corbould, 2008). Fishers have also been documented using cavities in trembling aspen (Populus tremuloides), lodgepole pine (Pinus contorta), and Douglas-fir (Pseudotsuga menziesii) trees in the cold-dry Chilcotin region of the province (Davis, 2009).…”