Fishing mink is a small carnivorous order with an average weight of less than 5 kg, and in our previous article, we have described how fishing mink has repeatedly killed much larger Canadian lynx than itself in the severe winter of food shortage, and it is no exaggeration to say that fishing mink is worthy of the title of "lynx killer". Today, we put aside the conflict between fishing mink and other predators, and through this article, we will talk about the attitude of fishing mink to its kind.
The historical distribution of fishing mink once spanned most of the northern forests of North America, but habitat loss, uncontrolled trapping, and systematic hunting led to a severe shrinkage of its range, and fishing minks were extinct from southern New England, the central and southern Appalachian Mountains as early as the early 20th century. In the decades that followed, the awakened humans realized the importance of animal conservation and actively carried out afforestation work, and after the habitat was improved, many areas began to reintroduce fishing mink populations.
From 1994 to 1998, Pennsylvania, located in the middle of the Appalachian Mountains, reintroduced 190 fishing minks from New York and New Hampshire, and due to the strong adaptability of fishing minks, Pennsylvania's vast forest area (about 58% of the state's area), coupled with appropriate conservation strategies, Pennsylvania's fishing mink population has been steadily rising for many years. In order to fill in the ecological information about the feeding habits of the fishing mink in this population, the scholar McNeil and others examined the stomach contents of the local fishing mink, and the results were unprecedentedly surprising.
McNeil et al. collected and examined the stomach contents of 91 fishing minks between 2002 and 2014, mainly in autumn and winter, of which 46 were male, 42 were female, and the remaining 3 were of unknown sex, 75 died in car accidents, 15 were trapped by animals, and 1 was of unknown cause. In addition to the 6 males, the researchers found stomach contents in the stomachs of other fishing minks, and considering that the bones of prey are often fragmented, hard parts such as hair, feathers, teeth and claws are most useful in identifying prey.
The results showed that the most important component of the fishing mink diet was mammals, with a proportion of up to 83.3%, and birds accounted for only 12.2%. The ratio of fruit to seed was 12.2%, in addition to 11% of the stomach found leaves. The most common prey is rodents, with a proportion of 48.9%, followed by carnivores (23.3%), and even-hoofed and rabbit-like orders account for 13% and 12%, respectively. By species, the most frequent occurrences in the stomach are white-tailed deer (13.3%), fishing mink (12.2%) and cotton-tailed rabbits (12.2%).
We can see that the same species is one of the most common prey species for fishing mink, and it is unprecedented to eat the same kind so frequently. Given that there has been little literature in the past to report on cannibalism by fishing minks, the researchers carefully examined these stomach contents to rule out as many examples of fishing mink combing hair as much as possible. If the stomach contains only the hair of the fishing mink and no meat, bones or claws of the fishing mink, then it may be that the fishing mink eats the hair into the abdomen while grooming. The results of the investigation showed that only 1 of the 12 cases were hair combing, and the remaining 11 cases were determined to be cannibalism.
Of the 11 cannibalistic minks, 6 died in a car accident and 5 were trapped in traps. The wreckage of a fishing mink in the stomach includes a large amount of hair, epidermis, and other hard parts. At least one claw was found in the stomachs of the eight fishing martens, many of which contained multiple claws, most of which were still attached to the distal phalanges, other phalanges, and toe pads.
Since 10 of these minks were collected from November to February, this apparently precludes the possibility of fishing mink preying on newborn young minks, as the mother gives birth to juvenile minks in the spring, usually in late March and early April. In addition, all the claws of the 5 fishing mink trapped by the trap were intact, indicating that the claws in the abdomen were not of their own, so it was impossible to explain the fishing mink remains in the stomach with self-mutilation.
Of the various medium-sized carnivores found in the belly of fishing mink, the most shocking thing is that the frequency of their species is so high. Cannibalism cannot be said to be very rare in some animals, and this behavior involves many factors such as population structure, life history, competition for mating rights, territory and food. But past studies have shown that cannibalism by fishing minks is rare or even unheard of.
Scholar Gabriel published a study on the mortality rate of fishing mink in California in 2015, according to statistics, 70% of the local dead fishing mink died of predation (90), of these 90 60 confirmed the identity of the murderer, and 8 were identified as cats, short-tailed cats (40%) and mountain lions (38%) killed the vast majority of fishing mink, 12% were unidentified cats, coyotes and domestic dogs accounted for 6% and 3%, respectively, the remaining 1% died from rattlesnakes, and none showed signs of similar predation.
Notably, California's fishing mink population is currently in trouble and relatively small, while Pennsylvania's population of fishing mink has been growing rapidly since the reintroduction of fishing mink in 1994-98, much faster than many subpopulations in the northwestern United States. How many fishing minks are there in Pennsylvania? The Pennsylvania Hunting Commission opened the trap season for fishing mink as early as 2011, with 126 trapped in the first year, up to 443 in 2014 and 398 in 2017.
In February 2018, the Pennsylvania Hunting Commission began discussing whether to lift the quota limit on mink trappers, while also considering allowing hunters to join in hunting fishing mink, and the head of the committee even blatantly suggested: "Let's change the law to catch fishing mink." Therefore, differences in population size and density may lead to differences in the degree of intra-species conflict in fish mink.
In 1999, the scholar Jelinsky published a study on the feeding habits of fishing mink in California, which pointed out that the same kind of hair was found in the feces of fishing mink, but all examples were attributed to accidental swallowing when fishing mink combed hair. In Pennsylvania, other tissues of fishing mink were also found in almost all stomachs containing fishing mink hair, which directly ruled out the explanation of false swallowing during hair trimming.
Regarding the wreckage of the same kind that appeared in the belly of the fishing mink, it has been speculated that it is the same kind of fishing mink that eats and dies, such as the same kind that was killed by a car, or the fishing mink claws are used as bait on the trap. After analysis, the researchers concluded that neither explanation was likely.
First, it seems illogical that local Pennsylvania white-tailed deer, raccoons, and North American possums die in car accidents far more commonly than fishing minks, which abandon this more easily encountered and tastier meat in favor of a large selection of dead ones, while also specializing in nibbling on the paws of the same kind instead of eating more meat.
Second, Pennsylvania's fishing mink trappers have a very limited annual quota, only one fishing mink can be caught per trapping season, and the claws are not sold with the fur, but the number of claws saved by the trappers is also limited, and the fishing mink is a non-picky predator, and the use of common, more accessible meat as bait is much more effective than the dry fishing mink claws, so the trapper is unlikely to use the claw as bait.
After ruling out these two possibilities, there is reason to believe that these fishing minks are likely to have killed and eaten a part of their kind, but it is confusing why the vast majority of fishing minks focus on eating each other's claws. The nutritional value of the claws is obviously lower than that of the meaty parts, and theoretically should not be the focus of the feeding area. In addition, the researchers' samples showed that it was rare for fishing minks to swallow their claws when eating other similarly sized prey species, suggesting that fishing minks treat their counterparts differently at the feeding site.
In light of this difference, the scholar McNeil proposed a hypothesis that the cannibalism behavior of fishing minks may be based on a driving factor unrelated to nutrient intake, that is, fishing minks do not eat the paws of the same kind because of hunger.
Due to the similar size of the claws in the stomach and the paws of predators, an example of intraspecific conflict in these species is likely to be adult fishing minks hunting adult or sub-adult counterparts. In addition, almost all of these fishing minks that eat the same kind are recycled in late autumn and winter (November to February), while small fishing minks are born in the spring and can grow up quickly in just a few months, so there is no possibility of infanticide in such a season.
Juvenile fishing minks are often born in March and April, and can become independent by autumn, but young fishing minks do not leave their mother's territory until midwinter or late winter to go out to work, and this spread period coincides with the time point of cannibalism of fishing minks. Apparently, when young fishing mink went out to roam, they inevitably had territorial disputes with other kinds, and some fishing minks died in the battle for territory.
As for why the fishing mink chose to eat the part of the foot claw, the scholar also gave the hypothesis that the victor swallowed the claw after killing the opponent in order to further eliminate the chemical odor on the opponent's plantar glands. The plantar glands of fishing mink were first identified in 1986, when scholars such as Bascock discovered plantar glands on the soles of fishing minks, American martens, wolverines and North American otters, which can be used to release chemical signals. Although this explanation is not unreasonable, it is not very convincing at present, and further research is needed to confirm it in the future.
Intraspecific conflicts among predators tend to increase with population density, and unlike most lower density populations, pennsylvania's fishing mink populations have increased dramatically over the past 20 years, in which case fishing minks are bound to erupt into more intraspecific conflicts over limited territory and resources. Because of this, the results of the study in Pennsylvania and other regions are very different, in addition to the mechanism of fishing mink eating the same kind and why they prefer to ingest paws, due to the lack of current data, experts can not make a fuller explanation, and it is hoped that future research will provide further insights in this regard.