I never heard of a habitat project designed exclusively for predators.
Most of the time, habitat work is geared toward aiding a species that is considered prey – ruffed grouse, deer, turkeys, ducks – you name it. The work carries great benefits not only for the intended species, but others as well. I like to see it.
But a project that took place recently on Forbes State Forest in Westmoreland County is unlike anything I’ve ever seen. Spearheaded by the state Bureau of Forestry, volunteers erected den boxes for fishers throughout the state forest.
A habitat project to aid a predator?
It’s certainly a unique concept when it comes to mammals. I never heard of habitat work to benefit any non-avian predator – fox, coyote, mink, weasel – nothing.
So the fisher den box is certainly novel and interesting, but what was the reason behind the endeavor? Fisher numbers aren’t declining in the state nor is their range shrinking. According to Pennsylvania Game Commission data from 2017, fisher populations were increasing were increasing in just about every region of the state.
That trend hasn’t changed. While the den box project at Forbes was obviously conducted with the intent to increase fisher numbers, it wasn’t done in response to a population that is in peril. In fact, an article that appeared in Pennsylvania Outdoor News noted that fishers are present in Forbes, but the forest lacks the natural tree cavities that they need to nest. As a result, the ability of the fisher population to increase at Forbes is limited. I don’t see that as a problem that needs fixed. If anything, the number of fishers at Forbes corresponds to the available habitat, and I’m leery of doing anything to artificially improve that habitat and inflate fisher numbers.
While fishers could thrive at Forbes as a result of the boxes, it’s possible that other species could regress.
The Allegheny woodrat, a state-listed threatened species, has a range that is restricted to a few slivers mainly in the southern half of the state. Among those slivers is the eastern edge of Westmoreland County – the same area where Forbes State Forest is located. Woodrat habitat is defined as rock outcrops surrounded by un-fragmented forest – the same habitat where fishers reside.
Encouraging an increase in the fisher population at Forbes wouldn’t be a good thing for the threatened woodrat.
A fisher diet study conducted by Indiana University of Pennsylvania and the Pennsylvania Game Commission from 2002 to 2014 found that rodents were their preferred prey. Studies in other states and Canada that examined both fisher stomachs and scat also found that small rodents were a common food source.
Woodrats are rodents.
The Allegheny woodrat isn’t the only declining species that is found in eastern Westmoreland County. The range of the West Virginia water shrew, which is also threatened, extends into area of Forbes State Forest. This diminutive critter prefers a forested habitat, like the woodrat and the fisher.
Since we know that fishers like to eat rodents, is it really a good idea to conduct a habitat project designed to increase their numbers in a part of the state that overlaps with two threatened small mammal species?
Still, it’s unlikely that the perils of the woodrat and water shrew are going to generate any uproar. If the den boxes do result in a few more fishers in Westmoreland County, and they eat a few more woodrats and water shrews, I doubt many people will even notice, no matter how harmful it could be to the limited populations.
Still, the den box project leads to a larger question: Do we really need to aid a predator whose population is already on the rise? And if so, what’s the benefit?
Or better yet, what’s the risk?
The biggest concern I hear regarding fishers is the impact they perceivably have on turkeys. It seems plausible that predatory fishers could wreak havoc on turkeys, and I’ve even heard some claims that they’ll climb trees at night and wipe out entire flocks.
But, going back to the stomach content surveys, this doesn’t appear to be the case. Turkey remains seldom turn up in the surveys, leading wildlife managers to believe that fishers aren’t killing them.
I think this conclusion is, well, inconclusive.
The majority of fisher diet studies occur in the fall and winter when carcasses are readily available from trappers. I could find little data of fisher studies conducted in the spring – a time of year when turkey and even grouse poults could be easy prey. Just because fishers aren’t eating adult turkeys in the winter doesn’t mean they’re not feasting on poults, or eggs, in the spring.
Snowshoe hares are another concern, and there is evidence to back it up.
A study conducted in British Columbia from 1988 to 1993 examined 255 fisher stomachs, and the snowshoe hare was the most common prey species. Studies in Wisconsin conducted in the 1990s also revealed hares were an important part of a fisher’s diet, as was the case in Maine, New Hampshire and Minnesota.
Considering the challenges that snowshoe hares, turkeys, ruffed grouse and other species are facing in Pennsylvania, it seems a bit counter-productive to conduct a habitat project designed to increase a species – fishers – that preys on them. Especially when fishers are doing fine on their own.
In fact, the best way to ensure a healthy population of any predator species is to improve habitat for the prey.
Fishers do have a place in Pennsylvania and they’re fascinating animals. I’ve seen them up close in the woods several times, and it’s always a thrill.
But the fact is their numbers are increasing and they’re doing well without our help. Improving the habitat for fishers in Forbes State Forest could unintentionally tip the scales against the prey species.
The den box project was well-intentioned, but it’s better to put the time and effort toward helping those species that are truly in peril, like the woodrat and water shrew.
- This column originally appeared in PA Outdoor News.
- Photo credit: Pennsylvania Game Commission
