Estrada, A. et al. 2004. A Survey of Black howler (Alouatta pigra) and spider (Ateles geoffroyi) monkeys along the río Lacantún, Chiapas, Mexico. Neotropical Primates. 12, 2 (Aug. 2004), 70–75. DOI:https://doi.org/10.62015/np.2004.v12.574.