| Quantifying reproductive parameters and characterizing habitat required for reproduction are essential to develop conservation plans for species of concern; however, studying reproduction in wild settings can be challenging, so local data are not always available. The fisher (Pekania pennanti) is an elusive carnivore with ties to mature forest features (e.g., cavities, large snags) that occurs across much of boreal North America. This species reaches the southernmost limit of its distribution in the southern Sierra Nevada in a population segment of conservation concern. Data on reproduction and denning habitat in this region are limited; therefore, I focused my dissertation on topics related to fisher reproduction in the southern Sierra Nevada, including: 1) reproductive parameters of female fishers here relative to those reported across the species' range, 2) denning habitat relative to resting and available habitat, and 3) attributes of tree cavities used for denning. In chapter 1, I reviewed literature on fisher reproduction over the species' range for comparison with 7 years of data from the southern Sierra Nevada. On average across its range, 71% of adult females reproduced (range, 40 -- 100%; n = 16), parturition occurred on 25 March (range, 3 March -- 17 April; n = 16), and litter size was 2.5 (range, 1 -- 4; n = 16). In our study area, we tracked 35 of 42 adult female fishers to 257 reproductive dens; 86% (range across years, 79 -- 100%) of females attempted denning and 75% (range across years, 64 -- 100%) were successful; mean parturition date was 30 March (range 17 March -- 12 April; n = 69), and mean litter size was 1.57 (range, 1 -- 3; n = 75). In this region, females reproduced at a rate comparable to or higher than elsewhere, gave birth at similar or later dates, but had the smallest reported litters; I discuss conservation implications of these findings and hypotheses for small litter size. In chapter 2, I compared fisher use of microsites and structures for resting and denning and assessed habitat selection by denning females at 3 spatial scales. At the microsite scale, both sexes rested in tree cavities (42.1%), branch platforms (29.7%), broken top platforms (11.1%), burrows (8.4%), and log cavities (7.5%); in contrast, females used tree cavities almost exclusively as both natal (100.0%) and maternal den (99.0%) microsites. At the structure scale, both sexes rested in live conifers (35.4%), live hardwoods (26.3%), and conifer snags (20.1%), while denning females used live hardwoods (51.3%), live conifers (22.5%), and conifer snags (21.3%). Both sexes rested most frequently in white fir (Abies concolor), California black oak (Quercus kelloggii), and ponderosa pine (Pinus ponderosa); denning females used California black oak most often (55.4%), followed by white fir and incense cedar (Calocedrus decurrens). Habitat selection analysis suggest that large California black oaks, large snags, dense tree canopy, high stand density indices, decay, slope, and elevation may predict den habitat at different spatial scales. In chapter 3, we assessed physical and thermal attributes of tree cavities used for denning and spatial attributes of den trees used in a single season by a female (i.e., den cluster). We measured physical traits of cavities used as den microsites (30 natal, 35 maternal); attributes were similar for natal and maternal dens, except that natal den entrances were smaller (mean vertical x horizontal diameter 11.1 x 7.6 cm compared with 19.2 x 9.3 cm). Data from loggers deployed inside and outside previously used den cavities (20 natal, 21 maternal) from late March -- June indicate that cavities provided good insulation from cold temperatures. Mean daily minimum temperatures were lower outside than inside cavities for all dens; natal den cavity interiors had a smaller proportion of days with temperatures below 5° C than maternal dens. Within a den cluster, mean distance between trees was 364 m +/- 314 SD (range 0 -- 1,894 m) and among all trees was 930 m +/- 650 SD (range 0 -- 2,718 m). Spatial attributes of den clusters may reflect a patch size relevant to denning female fishers that would be of use in forest planning. |
