The American marten (Martes americana) and fisher (Pekania pennanti) are closely related inhabitants of the Northern Forest region. Both species have been impacted by historical trapping and forest clearing. Disturbance to their forest habitat remains a threat, especially in northern Maine, where the two species overlap. To learn more about how marten and fisher coexist, how they might be affected by timber harvesting, and how to inform wildlife management and conservation efforts, researchers at the University of Maine conducted a nearly statewide survey of marten and fisher. Bryn Evans and Alessio Mortelliti used camera traps at 197 sites, taking more than 800,000 images over a period of four years. They then analyzed the images for marten and fisher occupancy patterns, which they then correlated with forest disturbance (based on satellite imagery), trapping intensity, and snow depth. Deeper snow is thought to favor martens, giving them access to prey and a refuge from fisher.
The study results, published in the journal Ecosphere in April 2022, show that habitat disturbance negatively affected both marten and fisher. “The effects of disturbance were always negative,” wrote Evans and Mortelliti. “Survey stations in areas that had more recent, or more intense, timber removal activities had lower probability of initial occupancy (marten), lower colonization probability (marten and fisher), and higher probability of [local] extinction (marten and fisher).”
These new findings are consistent with previous work indicating that forest modification impairs habitat for fisher and especially marten, which need both cover from predators and the dense tangles of undergrowth that host their small mammal prey.
Evans and Mortelliti were surprised by the lack of evidence for competition between fisher and marten. They didn’t find that deeper snow limited the distribution of fishers, or that fishers limited the presence of martens. Both were more likely to be found in forests with deciduous trees.
“It is possible there are enough resources for them to coexist,” said Mortelliti, “and it’s also possible they have found very finescale ways of partitioning habitat.”
To support populations of fisher and marten in the future, the researchers recommended preserving forested areas and corridors between them, keeping timber harvest activities moderate, and ensuring that hardwood trees in particular are retained, as well as older, decaying, hollow trees that both marten and fisher use to shelter their young.