Williams, L. E., Palughi, P. J., Cushman, A. et al. 1992. Vegetables as dietary enrichment for Saimiri. American Journal of Primatology 27, 63-64 (Abstract).

In all cases vegetables were consumed quickly, with celery and bell peppers being the preferred vegetables, followed closely by squash. String beans required more effort to eat and were usually the last to be eaten. ... This study indicates that vegetables can serve as an enrichment food for squirrel monkeys without detrimental clinical consequences.