A statement of facts

The phenomenon of a predator killing more than can be eaten is typically known as surplus killing. There is some disagreement as to the exact definition of surplus killing and what behaviours fall under it—for example, partially eating a kill and leaving the rest to rot is typically not considered surplus killing but rather a type of optimal foraging—but for the sake of simplicity we will use this term to refer to any killing that superficially seems “wasteful” and therefore apparently senseless. We will also take a look at a behaviour often called henhouse syndrome and compare it with surplus killing under more natural conditions.

Immediately it should be noted that surplus killing has been observed in a wide array of species and is not unique to Carnivora, never mind Mustelidae. It has been observed in avians, insects, and cetaceans, though this is far from an exhaustive list. Man is a prolific surplus killer, as is “man’s best friend”; indeed it is precisely the dog’s capacity for surplus killing that is exploited in hunting and pest control, and ultimately what earned dogs that appellation. There is nothing categorically unique about the predatory behaviour of mustelids.

Some may assert, possibly based on personal observation, that mustelids are more frequent surplus killers and that this is where the evidence for “bloodthirst” is. There exists no scientific data concerning per capita rates of surplus killing among carnivore species and anecdotal observations are subject to a number of statistical and cognitive biases (which will be examined later), so this evidence is specious at best. It is of course likely that predators with instincts for building caches for short or long-term storage of food are more prone to surplus killing, as are animals with higher metabolic rates or that live in climates with seasonal food insecurity (many members of Mustelinae fit all of these criteria), but one would be hard-pressed to attribute this surplus killing to malice rather than necessity, as these excess kills are likely to be consumed eventually. Indeed, cached kills are typically excluded from definitions of “surplus killing” as it is not in the spirit of wastefulness the term attempts to capture.

If the predatory behaviour of mustelids is not unique in quantity or character, where lies the bloodlust? Do mustelids have an unusually torturous method of dispatching prey? Do they display overt signs of joy when killing? The answer is no to both. Carnivores dispatch prey in whatever manner provides a sufficient balance of safety, ease, and expedience. Mustelids typically dispatch small prey with a bite to the neck or base of the skull; this is as swift and merciful as death can come in the natural world. Larger prey requires more time to subdue but, again, this is the result of necessity rather than malice. Compared to the methods of other predators mustelids are relatively “humane” in their killing of prey.

Likewise there is no evidence that mustelids take any particular joy in killing; at no point have we observed a mustelid in the wild displaying “happy” behaviours or vocalisations while hunting. The “weasel war dance” observed in some species in the subfamily mustelinae may appear during both hunting and play, but this is a sign of general excitement rather than a particular emotion, akin to the wagging of a dog’s tail (many a cynophobe has been made by the assumption a wagging tail means, “I am friendly, please pet me!”). Beyond this, fully mature mustelids seem to take hunting quite seriously. Prey is subdued as quickly as possible and immediately and unceremoniously hauled off somewhere for consumption or storage. At no point does the hunter take time to play with or otherwise revel in its kill.

This is not to say that mustelids experience no “thrill of the hunt”—a predator that receives no stimulation from hunting would likely not be long for this world—but there is no sign of anything resembling “bloodlust”. One may view any number of videos of mustelids hunting (such as those of the Joseph Carter the Mink Man channel on YouTube) to see they behave less like savage berserkers and more like disciplined soldiers; violent only for an intensity and duration appropriate to the situation.

Now that we have explained that mustelids are at least not any more bloodthirsty than any other carnivore family, let us take a quick look at animal behaviour and examine whether it makes sense to consider animals “bloodthirsty” at all.

“One who has not taken a Mink in a steel trap can scarcely form an idea of the terrible expression the animal’s face assumes as the captor approaches. It has always struck me as the most nearly diabolical of anything in animal physiognomy. A sullen stare from the crouched, motionless form gives way to a new look of surprise and fear, accompanied with the most violent contortions of the body, with renewed champing of the iron till breathless, with heaving flanks, and open mouth dribbling saliva, the animal settles again, and watches with a look of concentrated hatred, mingled with impotent rage and frightful despair. The countenance of the Mink, its broad, low head, short ears, small eyes, piggish snout, and formidable teeth, is always expressive of the lower and more brutal passions, all of which are intensified at such times. As may well be supposed, the creature must not be incautiously dealt with when in such a frame of mind.” – Coues, E.

Instinct versus intent

Wiktionary gives the definition of “bloodthirsty” as “thirsty for blood: inexorably violent or eager for bloodshed; murderous”. “Thirsty for blood” may describe any predator but only in the most trivial manner, as in a desire to lap up the blood from a recent kill. Quite clearly the term is normally used to describe an unusually passionate desire for violence and carnage, and usually has connotations of malice, evil, or wickedness. This term would not describe most forms of violence, such as hunting, self-defence, competitive martial arts, or even warfare for most soldiers. To defend its use to describe predators because they may have a literal thirst for blood is wholly disingenuous. It is a term to describe not just violence for its own sake, but deliberate cruelty and a particular revelling in the ending of life. This goes beyond describing the simple killing instinct found in animals.

Humans, to varying degrees, use logic and reason to carry out our goals. Our behaviour is deliberate to an extent beyond that seen anywhere else in the animal kingdom. Nonhuman animals, in contrast, are largely guided by instinct and impulse; their behaviour could be considered more “reflexive” and is usually best understood in simple terms of stimulus and response. This is likely where most observers fall into the trap of anthropomorphism—inappropriately attributing human motives, intentions, and rationales to nonhuman animals. While we humans are certainly still guided by our emotions and instincts, these are mediated by many cognitive processes and our behaviour is ultimately heavily influenced by our culture, social environment, morals, and personal understanding of the world. Other animals live much closer to their instincts and are innocent of such things.

“Bloodthirst” and other terms such as “vicious”, “malicious”, or “cruel” requires a level of malice aforethought that most predators simply cannot muster under normal conditions. The predatory instinct is a response to a prey animal’s stimulus. But if it must be compared to a human behaviour, we can speculate it is most akin to a young child dispassionately stepping on ants on the sidewalk. There is nothing but a simple intent to kill;  there is no overt bloodlust, no particular desire to cause suffering, no demonic whisperings in some dark recess of the mind, only the simple response of “step” to the stimulus of “ants”.

This concept can be difficult for some to grasp as the act of killing is very “loaded”, particularly for those whose upbringing was insulated from the realities of hunting and death. While not all killing is created equally, of course, there is no need to consider predation an exercise in evildoing. It may help to consider that animals are not moral agents and do not have, with perhaps a few exceptions, any understanding of the human concept of morality. Predators do not seek to do evil as they have no conception of evil; likewise, their understanding of a prey animal’s suffering is limited, if present at all. When a ratel (Mellivora capensis) emasculates a prospective predator it is likely not out of a conscious understanding that the testicles are the most painful place to bury a few sharp fangs, but a subconscious, instinctual intuition that a bite to the groin is a path to survival; this behaviour, of course, being ingrained in the species over millennia through natural selection.

Surplus killing and “henhouse syndrome”

As behaviour involves the brain—a biological organ—it is susceptible to evolution by natural selection. The instincts in particular are very “exposed” to the forces of evolution, lacking many of the checks and balances of higher cognition. It is a common misconception that natural selection produces “optimal” results—it would be more accurate to say it produces results that are “good enough” for survival and reproduction. Nature is not a conscious, rational entity with a clear end goal it works toward. Evolution is a complex interweaving of environmental, biological, chemical, physical, social, psychological, and ecological factors. Every animal we see is the result of a balancing act of all of these (often hidden) factors, and is not without its glitches and curiosities. We will not always immediately grasp the “reason” for a behaviour such as surplus killing, but that does not mean that one does not exist.

A predator’s instinct to hunt and kill is not necessarily tied to any immediate feeling of hunger. There are many potential reasons why these instincts evolved as such. Any killing provides valuable hunting experience and a refinement of the killing technique. For those animals with strong caching instincts surplus killing is a very synergetic behaviour. Brains are limited in their possible complexity and it may be “simpler” to have the killing instinct be a standalone process rather than dependent on other sensations, emotions, or mental processes. In some species this psychological “structuring” could be vestigial, a holdover from an ancestral form that for which it was more apropos. Any or all of these may be true in varying degrees for various predator species, but ultimately surplus killing evolved as it is for reasons of utility, or as a byproduct of the evolution of traits with more utility.

With “henhouse syndrome” a mammalian predator’s killing instinct is repeatedly triggered by the artificial abundance and confinement of prey. The killing instinct is typically triggered by the sound and movement of a prey item. There may be dozens of prey items inside a chicken coop, all in close proximity to the predator. Naturally, this tends to create a cacophonous flurry of movement which overstimulates the predator’s senses and instincts and sends it into a sort of frenzy. For a human this experience must be similar to being swarmed by flies, or perhaps paparazzi; violence naturally ensues, but more out of bewildered reflex than genuine malice.

Supporting this understanding is the frequent case that the survivors of these frenzies are those prey animals that did not move. It is likely not the case that the predator did not realise they were there, but simply that they did not stimulate the killing instinct. (It is just as unlikely that such a freeze response would save a monk from a Danish axe.) A 1977 study of questionable ethics investigated henhouse syndrome in Mustelinae by introducing weasels and polecats to groups of confined rodents. After the expected initial period of slaughter, it was found that within a day or so the introduced predators would adjust to the overstimulation and cease killing the rodents, despite the opportunity remaining available.⁽¹⁾ This indicates that henhouse syndrome is not an act of evil on the predator’s part, but the unfortunate consequence of behaviours evolved under natural conditions meeting the artificial abundance of human agriculture.

Before we move on, let us quickly address why surplus-killed chickens are often found in the coop completely uneaten. The immediately obvious reason is that, in the case of smaller mustelids especially, the prey often cannot be brought back through whatever hole the predator squeezed through to get in. The carcasses thus cannot be cached, and are abandoned. In some cases the carcasses are found neatly stacked in a pile—this would indicate the predator decided the coop would itself serve as a cache. In many cases the predator has lapped up the prey’s blood (this likely gave rise to the myth of the weasel’s supposed bloodsucking ability) or eaten a few bits and pieces, in which case this falls more under optimal foraging rather than surplus killing.

Also to consider is that most mustelids are not apex predators and themselves subject to predation. This has likely contributed to these predators being incredibly wary at times. The scent of a livestock guardian dog, the opening and closing of a farmhouse door, or the hoot of a distant owl could all be enough to snap a predator out of its henhouse frenzy and send it scrambling for safety. But, ultimately, we are discussing nonhuman animals; there does not always need to be a “good” reason for prey to be abandoned. Sometimes the killing instinct was activated and the subsequent caching instinct, for whatever reason, was not.

“A glance at the physiognomy of the weasels would suffice to betray their character. The teeth are almost of the highest known raptorial character; the jaws are worked by enormous masses of muscles covering all the side of the skull. The forehead is low and the nose is sharp; the eyes are small, penetrating, cunning, and glitter with an angry green light. There is something peculiar, moreover, in the way that this fierce face surmounts a body extraordinarily wiry, lithe, and muscular. It ends in a remarkable long and slender neck in such a way that it may be held at right angle with the axis of the latter. When the creature is glancing around with the neck stretched up, and flat triangular head bent forward, swaying from one side to the other, we catch the likeness in a moment – it is the image of a serpent.” – Coues, E.

Psychology and selection bias

From all of these observations we can draw the conclusion that the surplus killing in mustelids is best characterised as a simple instinctual response to environmental stimuli, and is likely unaccompanied by any ulterior motive that would be found in humans. So, why do people think mustelids are “bloodthirsty”? It is mainly due to a combination of statistical and cognitive biases. Small animals such as weasels generally have higher population densities than larger animals as they require less total resources to sustain themselves and thus more can survive in a given area. This means a farmstead may be home to more weasels than larger predators such as foxes, coyotes, bears, or mountain lions. Their small size likewise means weasels are better able to exploit flaws in poorly constructed coops to gain entry. These two simple facts combine such that weasels are observed preying on poultry somewhat frequently, even though poultry makes up but a tiny portion of their diet and any given weasel is not likely to ever prey on poultry.

The psychological factors are more convoluted, but can largely be attributed to anthropocentric thinking, the illusory truth effect, and the implicit stereotypes or attitudes that are inculcated since birth. Anthropocentric thinking is simply the tendency to apply human feelings and motives to nonhuman species, particularly when observing a behaviour that would seem irrational if a human were to do it. “Why did a stoat kill six of my chickens, pile their bodies up in the corner, and leave without eating them? It must have done it for fun.” This may contain elements of the fundamental attribution error, where an instance of a behaviour is wrongly attributed to a personality trait rather than circumstance. It is not immediately obvious that this hypothetical stoat killed the chickens as part of a natural hunting behaviour, determined the coop the chickens were in was a suitable caching spot and instinctively piled the bodies together—or, circumstantially, left the bodies as they could not be removed and taken to a more suitable caching spot—and left to resume hunting with the intent to return later for a chicken dinner. Instead, we believe the somewhat easier to comprehend idea that the chickens were killed for sport.

The illusory truth effect is the tendency to find a statement increasingly believable with exposure; “a lie told often enough becomes the truth”. One need only search for “weasel” on YouTube or any social media website or farming blog to be inundated with strikingly sensational language such as “bloodthirsty” or “savage” or “serial killer”. This largely characterises humanity’s understanding of the mustelids since at least the 19th century (and doubtlessly long prior), which has hitherto gone mostly unchallenged. There is simply a vastly greater quantity of misinformation than fact in this regard. Repetitive lies better lend themselves to verisimilitude than do novel truths; old myths enjoy a sort of inertia of belief which is difficult to overcome, and thus they persist.

The last factor is more nebulous. To put it bluntly, many people have a Disney-like understanding of animal behaviour: childlike, simplistic, allegorical, and, above all, easily digestible. Animals are prescribed as “good” or “evil” based on one’s own emotional response to the animal’s observed behaviour, rather than described impartially according to the animal’s behaviour in context to its biology, environment, evolutionary history, and ecological niche. This is typified by a response of anger or crying to the successful hunting of predators in a nature documentary—the prey animal is sympathised with as an innocent victim to the predator’s cruel oppression, and the more “cruelty” the predator displays in its hunting methods the more “evil” the predator is. This simplistic understanding is often stubbornly resistant to change, as some seemingly prefer to believe in such a thing as “evil” animals rather than apply some critical thinking to achieve a more accurate worldview.

Tying all of these factors together is the preponderance of mustelid villains in entertainment media. One can see our article on Weasel Stereotypes in Media for more information, but in essence the media we are exposed to can (mis)inform our beliefs in subtle ways. No, the media does not control our every conscious thought, but it would be just as absurd to say that it does not play a role in reinforcing culture—in this case, a culture of misunderstanding. How else could so many be convinced that wolverines (Gulo gulo) are the living incarnations of death and rage, when the vast majority of people have not and will likely never see a wild wolverine in their lifetime? The content we consume can, with repetition, result in implicit stereotypes and attitudes that colour how we perceive things. Just try imagining John Wayne as anything but a hardboiled frontiersman, or Patrick Stewart as anyone but Captain Picard; it might seem a bit wrong, somehow.

Conclusion

Ultimately, the mustelids are not the bloodthirsty berserkers they are often made out to be. They kill not for sport or out of malice, but by dictum of their instincts as determined by natural selection. They are not uniquely or disproportionately violent animals, and their killing technique is not particularly cruel. Their somewhat common appearance as coop raiders is the result of their relative abundance and the ease with which they can exploit flaws in coop construction, not out of spite for chicken farmers. If it made any sense at all to denounce an animal as “evil”, the mustelids would not be suitable candidates. There is no quality for which they are condemned that is not found and celebrated in the domestic dog.

References

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Commonly Misidentified and Misclassified Species | Surplus Killing: The Myth of Mustelid “Bloodthirst” |
Weasel Stereotypes in Media

Miscellaneous