1Cognitive Ethology Laboratory, German Primate Center, 2Courant Research Center for the Evolution of Social Behavior, University of Goettingen, 3Reproductive Biology Unit, German Primate Center
Friday 220, Plaza Level
An ability to employ tactical deception against conspecifics is argued to have been a factor favoring the evolution of increased encephalization and cognition in primates. However, few systematic observations of deception in wild primates exist, and no previous study has tested whether such behaviors are underpinned by cognitive mechanisms, or can be more parsimoniously explained by non-cognitive mechanisms. Previous research has shown that wild tufted capuchins (Cebus apella nigritus) use alarm calls deceptively to usurp food resources, with subordinates giving false alarms most often when food is more clumped and therefore more easily monopolized by dominants. This study tests an alternative to the cognitive hypothesis, namely that deceptive alarm calling is underpinned by the production of glucocorticoids (stress hormones). If the stress hypothesis is correct, it was predicted that competitive feeding would increase glucocorticoid production over baseline levels in subordinates more than in dominants, and that subordinates would be more stressed when food was more clumped. This was tested experimentally in Iguazú, Argentina by manipulating within-patch food distribution using feeding platforms suspended from tree branches and filled with bananas during a period of low fruit availabilty. Fecal samples associated with alternating clumped and dispersed conditions were collected from 18 individuals and analyzed for concentrations of glucocorticoids using validated enzymeimmunoassay. Results from one season of experiments do not support the stress hypothesis, with neither dominance rank nor resource distribution being significant predictors of glucocorticoid concentrations. Additional research is needed to determine if the deceptive behaviors are indeed underpinned by cognitive mechanisms.
This research was supported by an NSF International Research Fellowship and a Captive Care Grant from the International Primatological Society.