Opossum

COATI (Nasua narica )

Matthew E. Gompper, Ph.D.

Visitors to Barro Colorado Island usually find that white-nosed coatis (Nasua narica) are the most obvious component of the mammal community. They are readily seen because female coatis and young are gregarious and noisy by nature, and active during the day. Coatis are relatively numerous on the island, so chances of encountering some coatis on a short walk are quite good. BCI coatis have been the subjects of three long-term ecological studies as well as several shorter studies since the late 1950âs.

White-nosed coatis range from the very southwestern United States (Arizona, New Mexico and Texas) southward throughout Mexico and Central America (including all of Panama), and into northwestern Colombia. Ô White-nosed coatis are readily identified by their long, slender, non-grasping tail which is equal in length to the head and body, and by their long and flexible snout that protrudes beyond the end of the lower jaw. The claws are long and the feet are flat with naked soles. On Barro Colorado Island, adult males weigh approximately 5 kg and are approximately 114 cm from the tip of the nose to the tip of the tail. Adult females are smaller, weighing approximately 3.7 kg and measuring about 103 cm in length. On Barro Colorado Island the usual color is dark brown, nearly black, often overlaid with some silver. The ears are often white-tipped. The tail is ringed (more distinct in young than in adults) and generally held vertically while the animal is feeding. Laboratory studies that compare the DNA and proteins of coatis and other small carnivores confirm that the species is genetically most closely related to raccoons. Perhaps the most outstanding physical feature of a coati is its long, pointed snout. The area around the nose is rich in sensory receptors which result in an extremely heightened sense of smell. Numerous muscles allow great flexibility of the tip of the snout, which is used to poke into crevices and to seek out prey.

Coatis easily climb small trees and vines, and it can be very entertaining to watch a group of coatis feeding in treetops. They have more difficulty climbing the smooth trunks of large trees, and normally descend or ascend by moving out to the end of a limb and transferring to nearby branches of the same tree. Coatis can rotate their hind feet to descend from trees head first. The tail is not prehensile (that is, it cannot grasp), but does serve as a balancing tool during activity in trees. Coatis spend about 90% of their daytime hours foraging, and at least 90% of that foraging time is spent on the ground, even though they climb well. The forefeet contain long, powerful, blunt, and slightly curved claws, making coatis excellent diggers and shredders. Coatis are also strong swimmers, and on several occasions individuals have been observed swimming in the Panama Canal.

On Barro Colorado Island, all coatis breed at the same time within a two- to four- week period in late January and early February. After the mating season, males return to their solitary lifestyle, and pregnant females eventually separate from the bands to nest and give birth alone in a tree or den in April or early May. Gestation is approximately 70-77 days. Young coatis weigh about 180 grams at birth, with body lengths of 255-275 millimeters. They open their eyes after 4-11 days, and begin to walk and hold their tail erect at around 11 days. Teeth begin to erupt at about 15 days. By 40 days, when females and their newborn young rejoin the band, juveniles weigh approximately 500 grams. Females on BCI give birth to one to six young and rejoin the band with an average of 3.5 surviving juveniles. When first brought from the nest, juveniles are small, incompletely developed, and have difficulty keeping up with the band. In turn, the band appears to restrict its movements at this time. Mothers nurse their young for up to 3 months after band reunion, with most nursing occurring during the bandâs daily rest period. Adult females have been observed nursing, grooming, and baby-sitting the offspring of other females. Young males become solitary at the 24th or 25th month of age. Coatis are relatively long-lived: in captivity, individuals are known to live more than 17 years. On BCI, the oldest known individuals are at least nine years old.

Despite belonging to the carnivore family, coatis are quite omnivorous, eating mostly invertebrates and fruit, as well as vertebrates and carrion when available. Major events in coati life history on BCI are closely timed to food availability. For example, birth occurs during the period of greatest fruit ripening. During the wet season in Panama, 89% of foraging time is spent searching for animal foods such as insects and spiders, while in the dry season this proportion drops to 54%; the remaining time is spent under fruiting trees. Food is found by smell rather than sight, by sniffing in the litter, and then is dug up or extracted from under bark, leaves, or clumps of debris. Coatis handle invertebrate prey, even toxic species such as tarantulas, by rolling them between their paws, quickly killing organisms that can bite or sting, and removing the various hairs, bristles, and spines that may make the prey distasteful or difficult to Beat. Fruit is eaten both in trees and on the ground, and long climbs are commonly made to reach the outermost limbs of large trees. On Barro Colorado Island, Scheelea zonensis, Dipteryx panamensis, Spondias mombin, Ficus insipida, Quararibea asterolepis, and Tetragastris panamensis are important fruiting species.

Large cats such as pumas and jaguars, large hawks and eagles, snakes, and some monkeys prey on coatis. Much of the predation occurs on juveniles; one study on Barro Colorado Island found that 90% of the disappearances of juveniles occurs within three months of birth. Adult male coatis occasionally kill juvenile coatis. Although an adult coati can defend itself very well, predation on adults does occur: one of the authorâs adult male study animals was killed by a crocodile near the lab clearing, presumably while drinking or foraging near the shore of Gatun Lake. The $300 radio-collar the coati was wearing at the time of its disappearance continued to transmit radio signals for some time thereafter.

The population density of coatis on Barro Colorado Island is currently about 50-55 individuals/km2, which is higher than most other Neotropical sites that have been studied. However, large fluctuations may occur year-to-year due to disease or food availability, and periodic crashes in the BCI coati population have been recorded. On Barro Colorado Island, bands average 15 individuals, although this number may vary considerably within years due to mortality and the birth of juveniles. Bands are made up primarily of closely related individuals, although many bands also contain a few unrelated members.

Two very interesting behaviors have been observed among coatis that are indicative of the complexity and flexibility of coati behavior. First, BCI coatis have been observed to eat ticks from the coats of tapirs. This behavior is beneficial to the tapir who has parasites removed and to the coati who gets a protein-rich morsel to eat. Called a mutualistic behavior, it may have arisen when coatis and tapirs fed in close proximity at a feeding station in the laboratory clearing, and is likely culturally transmitted. It is presumed that coatis and tapirs do not normally mingle in the forest, but this is not known for certain. Second, and also likely learned, is the behavior of self-grooming and grooming of others with the resin of caraa, Trattinnickia aspera . This behavior is also likely acquired and maintained through cultural transmission, and may serve some pharmaceutical purpose.