after this author had left. During the 14 years the pair produced 10 young, all of which survived the first year. During four years no young were produced. In Vichada young are usually produced in December or early January. This is a difficult season with sharply reduced fruit resources for many animals in this part of the country (which has an annual precipitation of about 2400 mm; a long dry season is just taking hold and January and February present only a very few millimeters of precipitation for each month. A close analysis of the diet of the black titi here would be interesting, inasmuch as it would serve to identify the resources which allow the species to have this birth pattern. On the Guayabero River near La Macarena the birth season is apparently about the same time as in Vichada. On the lower Apaporis River in Vaupés with about 3815 mm of precipitation throughout the year, the birth season is also centered around December, although some outlying births are known as early as the first of October. Nevertheless, the birth season is the same as the other two sites, despite the lack of a strong dry season. However, we know that fleshy fruits are beginning to increase from their yearly low during this time, so the question of resource use by the species remains very interesting. Communication The black titi is very affectionate within the family unit, but the adult pair is aggressive towards neighboring pairs. The most common interaction with neighbors is counter-singing of the pairs, where one pair waits listening while the other pair vocalizes their duet, later the listeners answer, while the first vocalizers listen. There are instances when two pairs interchange vocalizations from very close together or from almost the same place in the forest. Sometimes these emotional interactions may finish in chases by the pair or an individual against the others. Rodríguez & Palacios (1994) found evidence of different types of agonistic interactions between different pairs. Vocalizations of this species are very complex, especially a long-call display utilized by these animals, perhaps to regulate spacing and defined territory. Surprisingly, experimental playback of solo male calls caused the owners of a particular territory to move away from the recording, and recordings of duetting caused the territory owners to duet in return and to travel parallel to the speaker. However, any approximate sound stimulus can cause