Hoopa Fisher Project

Female fishers give birth and raise their offspring in cavities in live trees and standing-dead trees. Fishers do not excavate cavities, but rather depend on fungal-decay processes or cavity-excavating species (e.g., piliated woodpeckers). Selection of habitat characteristics by reproductive females can mediate the influence of adverse environmental conditions on the fitness of offspring. Previous research has suggested that cavities and burrows used for reproduction by cavity-obligate species offer thermoregulatory benefits, access to prey, and can limit predation pressure.

In close collaboration with the Hoopa Valley Tribe, we hypothesized that female fishers select particular characteristics of reproductive den cavities at discrete stages of offspring development to mediate adverse biotic and environmental effects on their offspring.

We found that natal and early-maternal dens buffered minimum temperatures significantly more than late-maternal dens and cavities used during the nonreproductive season. A male fisher skull was also less likely to fit through the cavity openings of natal dens than through the openings of cavities used by adult females during the nonreproductive season. Litter survival was significantly lower at natal dens than at late-maternal dens. The age of adult female fishers did not affect the probability of litter survival. Our results emphasize the vulnerability of vertebrate offspring during early developmental periods and how cavity-obligate species select cavities to mediate environmental conditions during reproduction (Matthews et al. 2019).