Sometimes making strange noises in the forest brings about inquisitive faces. I still have not spotted a screech owl here in Missouri, and over the past week I have been checking out small hollows intensively. One appropriately-sized hollow seemed promising, and as I made a few brief “psh” sounds, a raccoon (Procyon lotor) from a large hollow nearby emerged to investigate me. It stayed in this position for about a minute, unsure of what to make of the situation, and eventually lazily climbed back down into the refuge to resume its nap.
If you’ve ever watched raccoons forage, you’ll notice they extensively use their forepaws in manipulating and investigating objects. Because of their handy demeanor, I considered them among the most dextrous carnivorans, but fine motor control is not what sets them apart. In fact, relatives that are exclusively arboreal tend to have greater manipulative ability, such as kinkajous (Potos flavus), olingos (Bassaricyon spp.), and the little known African palm civet (Nandinia binotata). Even many species of otters and bears rival raccoons in forepaw dexterity, as do pandas (Ailuropoda melanoleuca) and red pandas (Ailurus fulgens), the latter two which have independently evolved a false thumb for grasping!
What is so interesting about raccoons is that touch is the primary sense they use obtain information from objects in the environment. Whereas a civet or bear may visually inspect or smell a food item at length, raccoons use tactile cues to identify and localize objects. This behavior makes raccoons such alluring animals to observe, grasping at great lengths to interact and perceive things. I recently read an anecdote that raccoons sometimes turned their heads away when feeling for an object. This made me laugh, until I read the next line, that “humans often turn their head away when reaching for an object which they cannot see.” That’s right, why do we do that?? Although touch may be the go-to for raccoons, it may be that when visual cues are limited, we try to tune out those irrelevant sensory inputs, like closing your eyes to smell a flower. For raccoons, visual processing is probably less important from the outset. Similar behaviors have been observed in crustacean-eating mongooses (Atilax paludinosus) that forage in murky waters relying on their paws to localize prey.
Tactile specialization in raccoons may not be entirely reflected by increased dexterity when compared to its close relatives, but it does manifest in their sensory physiology and neuroanatomy. Generally, there is a positive correlation between the degree of sensory specialization and cortical representation within the brain. The underlying assumption is that a higher density of sensory receptors maps to a larger area of the cortex, which affords both greater acuity when detecting a stimulus and enhanced processing capabilities of that sensory modality within the brain. As predicted, raccoons, which rely heavily on tactile exploration, are characterized by a disproportionately enlarged somatosensory cortex in comparison to kinkajous and coatis. This confirms my suspicions that they are akin to moles, only above the ground’s surface 🙂
Receptor to cortical mapping often occurs in a topographic fashion, and raccoons are no exception. Specific regions of the palm and finger pads innervate particular subdivisions of the somatosensory cortex, allowing for spatial segregation of inputs within the brain. Keeping pathways distinct helps raccoons preserve the integrity of tactile cues before they are relayed to motor and decision-making centers of the brain. So, although raccoons may not have the most dexterity in their digits, they have a very accurate sense of what regions of the hand are in contact with an object and presumably fine discrimination of shape, texture, temperature, pressure, and movement.
Another common nocturnal North American inhabitant— the Virginia opossum (Didelphis virginiana). This old individual seemed completely unconcerned by my presence, ambling near me before stopping to yawn. Evidently, it had a nasty gash above one eye, and I couldn’t help but feel worried about its fate as the opossum kept walking towards an active eagle’s nest. Earlier in the day I had seen one of the two eagles ambush and kill a small waterfowl.