Abstract and Summary

The ecology and behavior of Tayassu tajacu and T. pecari were studied for a total period of 16 months in the years 1975–1978 in the Manú National Park in southeastern Perú.

It appears from 132 sightings of T. tajacu at the study site, and from reports from other regions, that groups of this species in rain forest usually contain fewer than 12 individuals. The more observers were at the study site, the more frequently this species was encountered. T. tajacu also repeatedly used wallows in the forest. These observations suggested that individuals of this species were relatively sedentary.

Herds of T. pecari were encountered on 60 occasions. Five counts indicated that there were over 100 individuals in the herds. This species was encountered at practically random intervals, independent of number of observers at the site, but more frequently in the dry season than in the rainy season.

Adults of both species are prey primarily of large cats and humans.

Both species feed on green plant parts, fruits, nuts and seeds, but T. pecari feeds on more resistant seeds and nuts than T. tajacu. The hardest palm nuts that only T. pecari can consume are distributed in a patchy manner. Cracking these nuts between the teeth causes the animals to be heard more than 50 m away.

The patchy distribution of the hard nuts and seeds prevents T. pecari from being sedentary, and group formation likely has several individual benefits for foraging efficiency and defense against predators. These may include (1) avoidance of searching for food in places recently visited by others, (2) benefitting from the knowledge of experienced foragers, (3) reducing the per capita probability of detection by predators, (4) reducing the probability of being captured after group detection by predators, (5) increasing the ability to counterattack as a group, (6) increasing the probability of detecting the predator before it can attack, and (7) “confusing” the predator through escape behavior.

T. tajacu seems to live in small groups because its typical foods are distributed more evenly and because consumption of these foods does not cause individuals to be so noticeable to predators.