black hawk eagle is a predator of the brown howler monkey. The roars of the brown howler allow the black hawk eagle to determine their location. The brown howler’s response has three parts. First, when one brown howler becomes aware of a black hawk eagle they will alarm the group and then they will immediately become silent. Next they descend in the understory of the trees, and finally they will all disperse in an organized manner. The adults will lead the young away from danger. The young are considered to be the primary target for the black hawk eagle. There is a more conservative response when adult brown howlers are without the young, and the black hawk eagle is present, thus indicating that the black hawk eagles are targeting the young howlers. When the brown howler monkey is threatened by terrestrial animals they will remain in the tree canopy and remain silent for 5–15 minutes. Rubbing Brown howler monkeys rub one another for group communication. The rubbing can be used for various purposes. Males will rub their hyoid bone and sternum against each other to show agonistic and territorial signals. Males will also rub females for sexual intentions. The males are considered to be the dominant over females because they rub much more often than females. Dominate females will rub more often than non-dominate females, but still much less than males. Reproduction It is difficult to breed the genus Alouatta in captivity and therefore the reproduction is relatively unknown. Brown howlers reproduce year round. There seems to be no correlation to birth rates in rainy or dry season or in times of increased fruit or leaves. It is thought that because the brown howler has a folivorous diet, conception is less dependent on maternal conditions. The average interbirth interval (IBI) for the brown howler is 19.9 months, which is similar to other howler species. It does not seem that the sex of the infant or the number of females in the population has a significant effect on IBI. The death of an infant will shorten the mother's IBI and seems to be one of the few factors that affects IBI. Yellow fever Brown howlers are highly susceptible to the yellow fever virus and have a high mortality rate when infected. When mass amounts of brown howlers are found dead it is a good indication that there may be a yellow