Enders, M. S. and S. B. Vander Wall. Black bears are effective dispersers of seeds, with a little help from their friends. Oikos 121:589-596.
See a related study: Vander Wall, S. B., K. M. Kuhn, and J. Gworek. 2005. Two phase seed dispersal: linking the effects of frugivorous birds and seed-caching rodents. Oecologia 145:282-287.