travels through the forest noisily, disturbing vegetation as it moves through. It has four main calls, which have been described as a "smooth chuck", a "bent mask chuck", a "peep" and a "twitter". Predators Predators of the Central American squirrel monkey include birds of prey, cats and snakes. Constricting and venomous snakes both prey on squirrel monkeys. Raptors are particularly effective predators of Central American squirrel monkeys. The oldest males bear most of the responsibility for detecting predators. When a Central American squirrel monkey detects a raptor, it gives a high-pitched alarm peep and dives for cover. All other squirrel monkeys that hear the alarm call also dive for cover. The monkeys are particularly cautious about raptors, and give alarms when they detect any raptor-like object, including small airplanes and even falling branches and large leaves. Predator detection by males becomes particularly important during the period when the infants are born. Raptors spend significantly more time near the squirrel monkey troops during this period, and prey on a significant number of newborn infants. Other animals that prey on Central American squirrel monkey infants include toucans, tayras, opossums, coatis, snakes, and even spider monkeys. Reproduction The breeding season for the Central American squirrel monkey is in September. All females come into estrus at virtually the same time. A month or two before the breeding season begins, males become larger. This is not due to extra muscle, but to altered water balance within the male's body. This is caused by the conversion of the male hormone testosterone into estrogen; thus the more testosterone a male produces, the more he grows in advance of the breeding season. Since males within a group have not been observed fighting over access to females during the breeding season, nor attempting to force females to copulate with them, it is believed that female choice determines which males get to breed with females. Females tend to prefer the males that expand the most in advance of breeding season. This may be because the most enlarged males are generally the oldest and the most effective at detecting predators, or it may be a case of runaway intersexual selection. Males sometimes leave their group for short periods of time during the breeding season in order to try to mate with females from neighboring groups. Females are receptive to males from other groups, although resident males attempt to repel the intruders.