I hope if you read this far in this four part series, that you enjoyed reading about one of the most enigmatic New World monkeys. Below is the list of works cited in the previous three parts, but I'm also going to include a few sources that are Internet accessible for those without quick access to the books and journal articles.
Google Image Results for "howler monkey"
Wikipedia Entry for howler monkey. This link includes some images including the one used to show schizodactyly.
Honolulu Zoo Fact Sheet
The Loudest Animal In the World, an article by Terry Dunn hosted by the Smithsonian National Zoological Park website.
Carpenter, C. R. (1934). A Field Study of the Behavior and Social Relations of Howling Monkeys.
Fleagle, J. G. (1999). Primate Adaptation and Evolution, 2nd Ed..
Gilbert, K. A., & Stouffer, P. C. (1989). Use of a ground water source by mantled howler monkeys (Alouatta palliata). Biotropica, 21(4), 380.
Kinzey, W. G. (1997).
Kitchen, D. M. (2004, 19/03). Alpha male black howler monkey responses to loud calls: Effect of numeric odds, male companion behavior and reproductive investment. Animal Behavior, 67, 125-139.
Milton, K. (1980). The Foraging Strategy of Howler Monkeys: A Study in Primate Economics.
Pinto. Liliam P., & Setz, E. Z. (2004, December). Diet of Alouatta belzebul discolor in an Amazonian rain forest of
Regan, B. C., Julliot, C., Simmen, B., Viénot, F., Charles-Dominique, P., & Mollon, J. (1998, November). Frugivory and colour vision in Alouatta seniculus, a trichromatic platyrrhine monkey. Vision Research, 38(21), 3321-3327.
Richard-Hansen, C., Vié, J.-C., & de Thoisy, B. (2000). Trnaslocation of red howler monkeys (Alouatta seniculus) in