My neighbor sent me some photos of a friendly looking raccoon (Procyon lotor) peeping into her house through a skylight. The photo came at the same time I happened to be reading about the domestication of urban raccoons.
What is domestication? In 1868, Charles Darwin observed that domesticated animals shared traits missing from their wild ancestors — shorter snouts, smaller brains, smaller teeth, floppy ears, white patches, prolonged juvenile behavior, and docility around humans, or tameness. Contemporary scientists have confirmed Darwin’s observation in urban foxes. A 2020 study of urban foxes in London found them with shorter and wider muzzles than their rural counterparts. This phenomenon may have transpired due to a reciprocal relation between diet and biomechanics. Urban foxes do not need jaw muscles as strong as rural foxes. Up to 37% of the urban dweller’s diet consists of scavenged food.
Or consider mice. In 2002, Swiss biologists enclosed 12 mice in sheds. Provided food and water, the mice reproduced until the population reached the size of a small hamlet, some 260 to 430 in number. Why? Because the mice could come and go as they pleased through openings that were too small for predators to pass through. The scientists monitored their safe space for more than 14 years (20 generations). Some mice didn’t like being handled and left. The mice that remained in the sheds lost their fear of humans and developed heads 3.5 percent smaller than wild mice. They also sprouted patches of white fur.
Something similar seems to be happening to urban raccoons. In the process of overcoming new urban challenges, they may be developing physical changes associated with domestication.
Snout length is an easily observed sign of domestication. Researchers at the University of Arkansas collected 19,495 images of raccoons on iNaturalist, of which 249 were high-quality and showed a complete head in profile. Dividing the images between rural (38) and urban (211), they concluded city raccoons bore snouts 3.56 percent smaller than their country cousins. Why? Again, possibly diet and biomechanics.
Domestication begins to occur when an animal species encounters humans. When we leave food waste behind, the animals may remain in our vicinity. Humans have the added benefit of scaring away predators. Humans also scare away large predators. So human-occupied territory has two things going for it — food and fewer predators. However, animals must still adapt. They must be cautious and careful around us, but not so afraid that they leave. Such is the initial stage of domestication. Over time, the animals with a reduced flight
response pass on their docility to their offspring. Over time, the animals with a reduced flight
response pass on their docility to their offspring.
Our domesticated animals — pigs, cows, sheep — have been selectively bred over many generations. After dogs became tame, we bred them for a variety of purposes, such as retrieving badgers in burrows (dachsunds), friendliness (pugs), protection (dobermans), pulling (huskies), speed (greyhounds), smelling (bloodhounds) or herding (sheepdogs). Nor does the process go on forever in straight line. Domesticated cats, for example, are an exception to the rule of the shorter snout. Wild cats typically have short snouts, which affords them the bite force they need but which also limits their sense of smell. Domesticated cat snouts cannot get much shorter without impairing their ability to smell. Therefore, domesticated cats have snouts that are similar in length to their wild counterparts.
Should you welcome the urban raccoon? Their snouts may be shortening, and they may look cute in photographs from your neighbor. But beware: they are still wild animals, sometimes carrying rabies, leptospirosis, salmonella, or the parasite that causes the flu-like toxoplasmosis. They can also carry canine distemper or the rash-causing feline parvovirus. Treat them with the same wary respect you would give to any other wild animal.
Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
Letter from a reader regarding a previous “Wild Things” article about rabbits and botflies:
Pamela J. says: “I read with interest the article [about rabbit botflies] in this week’s Day as I had a rabbit in my Riverside yard back in August, 2020, with just this issue. I had come to the wrong conclusion that it was rabbit papilloma virus but clearly it was this botfly larvae. . . . I had not seen the rabbit for quite a while and when it reappeared a month or so later, it was back to normal.”
Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
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