Snowshoe Hare (Lepus americanus) Range Contraction in Pennsylvania and Forest Features That Increase Population Resilience
Open Access
- Author:
- Zak, Amanda
- Graduate Program:
- Ecology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 20, 2025
- Committee Members:
- Duane R Diefenbach, Thesis Advisor/Co-Advisor
Cassandra M Miller-Butterworth, Committee Member
Jason Kaye, Program Head/Chair
David Andrew Miller, Committee Member
Emily S Boyd, Special Signatory - Keywords:
- Snowshoe hare
Lepus americanus
Climate change
Range contraction
Occupancy modeling
Species distribution modeling
Spatially-explicit capture-recapture
Forest management
Pennsylvania
Snowshoe hare
Lepus americanus
Climate change
Range contraction
Occupancy modeling
Species distribution modeling
Spatially-explicit capture-recapture
Forest management
Pennsylvania - Abstract:
- The snowshoe hare is well adapted to cold climates. A prey species, the snowshoe hare molts from brown to white pelage in the fall to camouflage against the snow and avoid predation. Pennsylvania’s winters are warming, and average snowfall is declining, causing hares to spend more time in winter-white pelage on a snowless background. Hares in this state of mismatch have higher predation rates. Range contractions tied to winter warming trends have already been observed in southern snowshoe hare populations. Across their range, snowshoe hare are associated with densely vegetated forest that provides visual cover from predators. In Pennsylvania, early-successional hardwood forest is an important cover type for snowshoe hare because the high density of regenerating stems provides both forage and cover. Sufficiently dense forest cover has the potential to offset the increased predation risk of hares in mismatch, but the amount of early-successional forest has been declining in Pennsylvania over several decades. With this dual threat of warming winters and declining early-successional forest cover, the status of the Pennsylvania snowshoe hare population needed to be assessed. I first designed a single-season occupancy study that followed the methods of a previous 2004 study. My goal was to determine if the Pennsylvania snowshoe hare range had contracted since 2004. I created occupancy models fit to field survey data from 2004 and 2023, which showed that a range contraction had occurred, coinciding with declines in winter snowfall. This range contraction was greater than had been predicted by the 2004 study. I further found that occupancy models fit to the 2004 survey data were unable to predict occupancy in 2023, even when exact values for climate and forest conditions in 2023 were used to generate the prediction. This study is one of only a few that have explicitly evaluated species distribution model projections with long-term data sets, and I showed that model projections may be wrong and cannot be reliably evaluated until time has passed and new field data are collected. After identifying the rapid contraction of the snowshoe hare range in Pennsylvania, I designed a second study with the goal of providing guidance to state land managers on managing forests for snowshoe hare. I applied spatially-explicit capture-recapture modeling to non-invasive genetic sampling of fecal pellets on 10 forested sites in northwest Pennsylvania, a region where hare occupancy probabilities were high. I identified forest age class and forest understory density as important forest characteristics related to snowshoe hare population density. Snowshoe hare densities were higher in denser forest understories. Early-successional forest was able to support greater population densities than mature forest for the same forest understory conditions, but I observed the highest snowshoe hare densities in mature forest with mountain laurel and eastern hemlock understories. Under simulations, I showed that both stand-replacing harvest to create early-successional cover and improvement of mature forest understory densities have the potential to increase snowshoe hare population densities. Although the expected increases in hare population density after forest management actions were small, higher population densities are related to lower extinction risks; therefore, forest management can increase the resiliency of the Pennsylvania snowshoe hare population under warming winters by maintaining and increasing population densities.