The New Neotropical Companion

throat sac and huge tracheal cartilages that act as a

resonator, dramatically amplifying their calls. Howling

serves to mark the troop territory; because the howling

carries for nearly 1.5 km (1 mi) through rain forest,

two troops can come to a mutual agreement about real-

estate boundaries without necessarily ever meeting

one another.

Male howlers are approximately 30% larger in body

size than females, and this difference, plus the unique

male vocal apparatus, suggests strong sexual selection

in this species complex. An average howler clan

consists of three adult males, seven to eight females,

and varying numbers of juveniles. Clans vary in size,

however, ranging from four to 35. Males are dominant

over females, and young animals tend to be dominant

over older animals. Monkey troops frequently engage

in mutual grooming behavior, an important behavior

in maintaining troop cohesiveness.

Howlers live in many forest types (mature and

disturbed forests, gallery forests, semi- deciduous forests,

lowland and lower montane forests) and, wherever they

occur, specialize on a diet of leaves, with fruit and flowers

making up only about 30% of their diet. Because they

rely so heavily on leaves, they tend to have fairly small

territories. Why small? Well, leaves are pretty abundant

in rain forests, so for howlers food is pretty much

everywhere. This is not to say that all leaves are equally

tasty or even equally safe— far from it (recall chapter

11). But leaf biomass assures sufficient palatability to

allow territories to be small, and that means howlers

Plate 16- 19. This red howler monkey is sounding off, making

his troop’s territory well known. Photo by Gina Nichol.

Plate 16- 16. A family of red howler monkeys (Alouatta sp.).

Mothers are very protective of their offspring. Photo by

Andrew Whittaker.

Plate 16- 18. This female Black Howler Monkey had given birth

in this tree just minutes before this photo was taken. Her infant

is clinging to her underside. Female Black Howlers are tawny-

colored; only the males are black. Photo by John Kricher.

Plate 16- 17. Male Black Howler Monkey grasping a branch

with its prehensile tail. Photo by Andrew Whittaker.

chapter 16 from monkeys to tarantulas: endless eccentricities 327