Found throughout much of Brazilian Amazonia, the bearded sakis (Chiropotes albinasus and Chiropotes satanas) are primates specialised for seed predation. In order to delineate activity patterns and the exploitation of dietary resources, two social groups (10 and B4) of C. satanas were monitored between July and November, 2001, at the reservoir of the Tucurui hydroelectric power station in the state of Pará. Group 1G (C.s. utahicki), with 24 members, occupies an island of 100 ha, whereas group B4 (C. s. satanas), with 27 members, inhabits an area of continuous forest, both protected by Eletronorte S.A. Quantitative behavioural data were collected in scan samples, with a 5 min interval, collected continuously during five days per month. Complementary observations were recorded in ad libitum fashion throughout the study period, which started in April. A total of 5490 reords were collected for group 1G (only the feeding behaviour of group B4 was analysed here), distributed between feeding (58,8%), locomotion (30,8%), rest (9,5%) and other activities (0,9%). These proportions varied considerably between months. One hundred and ten plant species were exploited by the sakis. As expected, seeds were the main dietary item in both cases (group 1G: 75,6%, n = 2721 records; group B4: 49,6%, n = 1865). Remaining dietary items included flowers, fruit, leaf shoots and the mesocarp of palm fruits, although insectivory was not observed. Similar variation in the consumption of different items was observed in the two groups between September and November. Taxonomic diversity of the diet of group 1G was greater than that of B4, as was its home range (100 vs. 57 ha). No systematic variation was found in foraging party size. The results of the study indicate that the remnant populations of bearded sakis in the region's fragmented landscape have good long-term potential for conservation.
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