Intra- and inter-specific social learning was investigated in two species of

New World monkey, the saddle-backed tamarin {Saguinus fuscicoUis) and the redbellied

tamarin {S. labiatus), which form stable and permanent mixed-species troops in

the wild. We explored whether improved food acquisition, through social learning, is a

potential advantage of mixed-species troop formation by allowing a pair of naive

observers to watch a pair of trained demonstrators complete a novel foraging task. The

aims of the study were (a) to determine if individuals succeeded at the task more

quickly after having observed demonstrators, (b) to investigate whether speed of

acquisition differed after observation of conspecific demonstrators as opposed to

congeneric demonstrators, and (c) to compare performance between species. The

number of trials taken by observers to succeed on the task was compared with that taken

by naive demonstrators to succeed on the task initially. Individuals succeeded on the

task more quickly if they had had the opportunity to watch demonstrators perform the

task, regardless of whether the demonstrator was a conspecific or congeneric. There was

no difference in performance between species. It is concluded that, for both species, the

learning of a new foraging technique is facilitated by the presence of both conspecifics

and congenerics and that the likely mechanism for this facilitation is a combination of

stimulus enhancement and response facilitation. Social learning of this kind is discussed

with respect its adaptive value in wild mixed-species tamarin troops.