Baumgarten, A. and Williamson, G.B. 2007. Distribution of the black howler monkey (Alouatta pigra) and the mantled howler monkey (A. palliata) in their contact zone in eastern Guatemala. Neotropical Primates. 14, 1 (Jan. 2007), 11–18. DOI:https://doi.org/10.1896/044.014.0103.