Dietary analyses of fishers

Zoologist Roland Kays in his New York Times article, Do Fishers Really Eat Cats? expresses scepticism: “I hear stories of mountain lions in the hill towns and even a population of Bigfoots in the Adirondacks. Tell me you saw a deer today and I have no reason to doubt you, but if you make a claim that has never been verified, I want to see the data. Since cats fight each other all the time, and a black cat would look an awful lot like a fisher, witnesses’ accounts take us only so far.”⁽²⁾ Kays, at the time researching fisher behaviour in and around Albany, New York, performed a small investigation of 24 fisher diet samples and 25 kill sites. This resulted in no evidence being found of fishers preying on cats.

Of course, one small survey proves nothing; what do larger, more rigorous dietary analyses find? Well, among the analyses available on the internet, only two studies have found evidence for fisher predation of cats at all. One of these does not appear to be available on the internet itself but has been referenced by other sources.⁽³⁾⁽⁴⁾ This study, apparently conducted in New Hampshire between 1979 and 1980, found cat hair in only one out of over one thousand fisher stomachs. Unfortunately, these secondary sources do not state when and where the samples were collected, but clearly these fishers were not the cause of the many lost cat posters found across New Hampshire.

The second of these studies, conducted between 1992 and 1994 in a 210 km2 (81 mi2) area in Worcester County, Massachusetts, found cat remains in two percent of 226 fisher scat or stomach content samples⁽⁵⁾. The majority of the scat samples were collected from the study’s 92 radio-tracked fishers, and the 57 stomachs were provided by trappers. So, among the at least 149 fishers in the study area, only about five cats were recorded to have been consumed. This study also includes 34 observations of prey remains and witnessed kills by fishers, of which two were of cats, and only one was a witnessed kill. While two percent is certainly larger than one-tenth of a percent, these results are still incongruous with the perception of fishers as avid cat-hunters.

There are a few things that are important to note about scat analyses. First: they cannot distinguish between predation and scavenging. Outdoor cats have much greater exposure to predation, disease, poison, and traffic compared to indoor cats, and fishers are facultative scavengers⁽⁶⁾. It is not unlikely that at least some accounts of fishers carrying away dead cats are explained by scavenging rather than predation. Second: scat analyses tend to overestimate the consumption of larger prey versus smaller prey. Small prey, such as mice, will pass through the digestive tract in a smaller number of droppings relative to larger prey, which may be fed on across multiple days and may appear in multiple droppings. Given that cats and fishers are generally comparable in size, it is not unreasonable to think that multiple droppings could contain fur from the same cat. Lastly: scat analyses cannot provide information about what is not eaten. It is sometimes postulated that fishers kill cats simply to eliminate competition. This is not an unreasonable hypothesis; however, this behaviour is no less risky and energy-intensive than hunting. As fishers are not picky eaters, it is likely their competitors would be consumed after a fight, and thus appear on a diet analysis.

Now, here is a non-exhaustive list of fisher diet analyses that did not report finding any cat remains: Arthur, Krohn and Gilbert, Maine, 1984-1987, 68 samples;⁽⁷⁾ Brown and Will, New York, 1975-1977, 405 samples;⁽⁸⁾ McNeil et al., Pennsylvania, 2002-2014, 91 samples;⁽⁹⁾ Van Why and Giuliano, Vermont, 1996, 197 samples;⁽¹⁰⁾ Giuliano, Litvaitis and Stevens, New Hampshire, 1965-1967 and 1987, 331 samples.⁽¹¹⁾ Excluded from this list are studies conducted in wilderness areas where outdoor cats are present in low quantities, if at all. On the contrary, these studies are from the northeastern United States, where outdoor cats are common—Vermont and Maine are the top two states for cat ownership⁽¹²⁾, and 40% of 184 cat owners surveyed in Massachusetts allowed their cats outdoors^(13)—and where the perception of fishers as cat predators is strongest. While these studies may be a bit dated and fishers have grown increasingly adapted to suburban environments, fishers have long been rumoured to prey on cats and Kay’s research suggests suburban fishers prefer to supplement their diet with squirrels rather than pets.

Dietary analyses of other predators

Compare the results of these diet analyses with those of coyotes, likely the most common wild predator of outdoor cats in North America. While coyotes, like fishers, eat fewer cats than commonly assumed, cats can be an important food source for coyotes in some locations. Larson et al. found cat fur in 22% of 119 coyote scats collected in San Diego, California from 1995 to 1997 (interestingly, this study also found cat fur in two out of 58 grey fox scat samples).⁽¹⁴⁾ Quinn found cat fur in 7.8% of 1,435 coyote scats collected in western Washington state from 1989 to 1990.⁽¹⁵⁾ Grubbs and Krausman, while tracking eight coyotes in Tucson, Arizona from November 2005 to February 2006, observed 36 coyote-cat interactions with 19 ending in successful predation; additionally, they recorded 45 instances of coyotes consuming prey, of which 19 were cats.⁽¹⁶⁾ These studies represent the extreme cases, but even studies with more “moderate” amounts of predation often find cat hair in one to four percent of samples. Fisher diet analyses, however, typically find nothing.

Now, if diet analyses suggest that fisher predation of cats is at most very rare, why are there so many reported accounts? Are these analyses flawed in some way, or are these accounts simply not credible? Some of them surely are credible—fishers are opportunistic predators and likely do take the odd cat, especially when their preferred prey is sparse—but part of the issue is the general public’s difficulty in identifying fishers. One only need to spend time in animal identification forums to see this; everything from raccoons to grey foxes, red foxes, to groundhogs and porcupines are often misidentified as fishers, even by avid outdoorsmen. Conversely, fishers are often mistaken for North American minks, wolverines, badgers, mongooses, and even black bear cubs. This alone adds some uncertainty to eyewitness accounts, and if these supposed fisher attacks happen at night (fishers tend to be nocturnal outside of the winter season) they become more difficult to take at face value.

Correlation does not imply causation

Another confounding factor is the myth of the “fisher scream”. A YouTube video titled, Fisher cat sound by user Nature Magazine (the account is not affiliated with any publication or organisation) illustrates this myth. Despite its title, the recording features the scream or bark of a red fox. Here is a video on YouTube that demonstrates a red fox scream, here is another. In New England particularly, unfamiliar animal calls (typically red fox screams, but bobcat and raccoon vocalisations are also common) are often attributed to fishers. Juvenile fishers do have a piercing distress cry they make when threatened, as as shown in this video, but this is a very rare sound to hear in the woods; adult fishers are likewise very quiet. Despite this, it is not uncommon to see accounts of fisher predation justified by hearing “fisher screams” on the night of a cat’s disappearance.

Even more specious are accounts of feral cat colonies disappearing after a fisher is spotted nearby. One of the fundamental tenets of science and critical thinking is correlation does not imply causation. Fishers are famously elusive, and spotting one in the wild is a cause for celebration among wildlife enthusiasts. Fishers may be present in an area well before they are seen, and the disappearance of feral cats is likely only coincidental. It is not uncommon for disease to spread through a cat colony, and it is possible the abundance of cats weakened by illness could be what motivated the fisher’s appearance in the first place. On a broader scale, the reappearance of fishers in the Northeastern U.S. generally coincides with colonisation by coyotes (which can also be quite elusive). These factors, combined with the lack of scientific support for fisher predation of cats, make these accounts very unconvincing. It is also worth pointing out that cat owners rarely talk about their pets not being attacked by fishers, despite being in fisher territory.

Finally, because the reputation of fishers as cat-killers is so entrenched, fishers are often blamed for the disappearance of cats with no reasoning whatsoever. As 30-year veteran of the New Hampshire Fish and Game Department Eric Orff states: “‘Fisher cats’ are blamed for dozens of missing cats each year. Do they eat cats? Sure, as do foxes, coyotes, owls and – more likely – a local SUV. It is the nature of a housecat injured on a highway to seek a hiding place to die, but you can bet a ‘fisher cat’ will be blamed for its disappearance.”⁽⁴⁾ Beliefs are known to influence perception.⁽¹⁷⁾ Thus, it is not unlikely for the distant, dark silhouette of a fox hauling off a squirrel dinner to be misinterpreted as a fisher carrying away a cat.

None of this is to say it is impossible for a fisher to hunt a cat. Fishers are very capable predators for their size, and cats could be a “survival food” when times are tough. However, the evidence does not support the idea that fishers prey on cats with any regularity. This perception likely stems from an entrenched cultural belief that has taken on a life of its own, and within which is buried only a small grain of truth. As fishers provide important ecosystem services such as preying on rabid raccoons⁽⁵⁾ or tree-killing porcupines⁽¹⁸⁾, it is important that they are not unduly feared or hated.

Conclusions

Further research is needed to fully understand the dynamics of fisher-cat interactions and the true extent of fisher predation of cats. In the meantime, the general public should understand that fishers are very low on the list of potential threats outdoor cats face. Coyotes, cars, disease, poison (including secondary exposure to rodenticide), and conflict with other outdoor pets are all proven sources of cat mortality. If a cat owner is not already concerned about these major risks, there is no cause to be alarmed by the sight of a fisher. And for those with no such concerns, there is arguably only one proper response to seeing a fisher: an expression of awe and gratitude for the privilege of spotting one of North America’s most elusive predators.

References

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