Five species of titi monkey (Callicebus brunneus, Callicebus caligatus, Cal
licebus cinerascens, Callicebus donacophilus, and Callicebus moloch) were r
ecorded in surveys of primate populations at 26 sites throughout the Brazil
ian state of Rondonia. The distribution of the two species, C. cinerascens
and C. donacophilus (recorded in the state for the first time), appeared to
be related to that of non-forest ecosystems, the former in the cerrado woo
dlands, and the latter in gallery forests of the Guapore grasslands. The re
sults of the surveys also indicate that C. brunneus has a more restricted d
istribution in southern Rondonia than was previously thought, whereas C. mo
loch is more widespread. However, the ecological factors that determine spe
cies distribution in the south of the state remain unclear on the basis of
the available data. All species were observed in small social groups of no
more than five individuals, which are typical of the genus, generally in th
e middle and lower forest strata.