Sunday 21 May 2023

The Raccoon Family: Kinkajous - the primate-like "raccoons"

Raccoons proper are well-known animals, both familiar and distinctive even to those of us living in countries where they are not native. Among the other members of the raccoon family, coatis are at least familiar to people in the southern US. Ringtails ("cacomistles") are probably more obscure, being smaller and mostly active high up in trees at night, but at least, they too, live in the US. The remaining species, however, live only in Latin America and it's probably fair to say that they are much less familiar to English speakers than those groups with more northerly representatives.

Perhaps the most distinctive, and certainly the most studied, of these is a genus with just one species: the kinkajou (Potos flavus). It was first scientifically described by Johann Schreber in 1774, in an earlier volume of the book in which he would later describe (among other things) cheetahs, snow leopards, and bobcats. While he was understandably clear those were all cats, the identity of the kinkajou was not so obvious. In the days before Darwin, this may not have held any deep meaning for him, but his conclusion was that his new animal was a kind of lemur.

In all fairness, it's easy to see what he was thinking. The kinkajou does look much like a lemur, and it has similar habits, too. Even so, just a few years later, he gave it a new name, apparently unaware that this second, South American, specimen came from the same species as the first since he'd been wrongly told the original came from Jamaica. This time, however, looking at what we now know to be the same creature, he grouped it with the civets. Indeed, kinkajous were still grouped with civets by later authors even after St Hilaire and Cuvier jointly created the current genus Potos for it. 

Kinkajous have a similar body length to a raccoon, but are much slimmer, even without the fluffed-up fur that makes the common raccoon look larger than it is. They have a relatively uniform tan colour, and have not even a hint of striping on the tail, which certainly reduces their resemblance to their better-known relatives. They live through most of the northern half of South America, and as far north as southern Mexico, inhabiting a wide range of forest types, from the dense jungle of the Amazon to the sparser woodland of the Cerrado. Several subspecies have been identified from across this range, and it has even been argued that some of these might be distinct species - although nothing seems to have come of this suggestion.

Kinkajous are almost entirely arboreal, spending as little time as possible out of trees and then only to travel between them as quickly as they can. They are also about as firmly nocturnal as its possible for an animal to get, heading out around a quarter of an hour after sunset and returning home a similar time before dawn. Both of these features naturally make them difficult to spot and setting up camera traps to see how common they are may not help, since they tend not to go back to places where they have previously seen the flash photography needed to view them in the darkness. Despite these limitations to possible population studies, they seem to be both resilient and relatively numerous, and they are not considered a threatened species.

Highly adapted to their arboreal habitat, kinkajous can reverse their feet, swivelling them to point backwards on the ankle. Combined with the gripping claws on their toes, this makes it much easier to climb trees. Cacomistles can do this too, having similar skeletal adaptations, but the kinkajou also has modified muscles that make it easier, as well as stronger hind-limb muscles to enable them to hang from their feet. Other muscular adaptations also correlate with travelling in trees, including an enlarged muscle in the neck common in many arboreal primates and used in swinging from branches- although the apparent human analogue is vestigial and normally missing altogether.

Add this to the fact that, uniquely among members of the raccoon family, the kinkajou has a prehensile tail like that of certain monkeys, and the similarity to primates becomes even more stark. The gait that they use while walking along branches is also primate-like (and, indeed, also resembles some tree-climbing marsupials) despite the lack of the prehensile toes that monkeys tend to have. 

The resemblance to primates doesn't end there, because the kinkajou also absolutely loves eating fruit. In fact, they eat little else, with one study estimating that around 90% of their diet consists of fruit, with various kinds of fig apparently being their favourites. At least in the wild, the other 10% seems to be comprised of leaves and flowers, all eaten while travelling in the tree-tops. In captivity, kinkajous have been seen eating the occasional insect, and it's probable that they do this in the wild too, but this is such a minor component of their diet that we can fairly describe them as herbivores, something that's obviously unusual among members of the order Carnivora. While there is no evidence that they can fully ferment the fruit they eat in their stomachs, their digestive processes otherwise seem similar to that of highly frugivorous primates such as spider monkeys. 

One respect in which we might expect that they wouldn't resemble primates is their social organisation. Other members of the raccoon family are solitary, and, indeed, when we see adult kinkajous travelling about to feed, they typically do so on their own. A couple of kinkajous fitted with radiotracking collars in French Guiana showed that each occupied an area of between 15 and 40 hectares (35 to 100 acres) and travelled 1.5 to 2.5 km (1 to 1½ miles) each night. The male tended to use his daytime roosts at the edge of his territory, perhaps to make it easier to keep a lookout for rivals, while the female did not, but both had several such roosts to choose from and tended to take a rest around midnight.

When they are not feeding, however, or when they find a fruit tree large enough to share, kinkajous can be much more social. Their groups are, to be sure, much smaller than those of monkeys but it's still more than we'd see in common raccoons. A typical group apparently consists of two adult males and one adult female, together with a couple of younger individuals. Like primates, members of these groups groom one another, removing parasites from parts of their partners' bodies that they could not reach on their own.

Unusually for mammal species, the groups are patrilineal, with males tending to stay with their mothers and the females leaving to find unrelated partners elsewhere. The imbalance in gender leaves some females living on their own, hoping to find a group to join - the opposite situation to most mammals, where it's the males that tend to do this.

Analysis of relative brain size among members of the raccoon family shows that the brain regions that, at least in humans, are related to social planning and organisation are no larger in kinkajous than  true raccoons and that it's the more sociable coatis that win out in this respect. They do, however, win out when it comes to brain areas related to agility, which makes sense given their arboreal lifestyle, while true raccoons come top in the areas related to manual dexterity. 

Kinkajous do scent mark their territory, and presumably have a sophisticated sense of smell, and use a wide range of different sounds to communicate with one another. On the other hand, perhaps because they are nocturnal, kinkajous do not seem to have the sort of colour vision that monkeys do, even though this would help them determine whether fruit is ripe if they were to see it during daylight.

Females give birth to a single young and care for them alone, although this takes a comparatively long time to do, since the young are not weaned until eight weeks and cannot travel through the trees until thirteen. Although the mother will sometimes carry her young about in her mouth to get around this, more often she simply leaves them alone in her sheltered nest while she goes off to find food. Paternity analysis has shown that female kinkajous are largely monogamous in the sense that they primarily (but not universally) mate with the dominant male in their group, or with the nearest dominant male if they happen to live alone. The presence of those solitary females, however, means that the males are certainly not monogamous, although they do not seem aggressive in driving off potential rivals.

While kinkajous have been widely studied because of their parallel evolution with primates, the same is not true of the remaining species of the raccoon family native to Latin America. Remaining generally more obscure than their prehensile-tailed kin, is to these last few species that I will turn next time...

[Photo credited to the Kalamazoo Public Library, from Wikimedia Commons.]

No comments:

Post a Comment