Behavior

Activity Patterns

Mantled Howlers are diurnal (active during the day) and arboreal (adapted to live in trees). While traveling around during the day, howlers will often find a pleasant spot and spend a considerable amount of time in this spot if it fits all of their needs. Their movement is determined in part by environmental factors (the heat). During the dry season when heats are considerably higher than the rest of the year, howlers have two peak movement periods during their day. The first activity occurs early in the mourning following their "dawn chorus," and the second period is in the late afternoon when temperatures have cooled off again like early mourning. When the rain season begins, howlers increase their activity. This cooler weather allows them to move about more freely and not exhaust so much energy in the process. Howlers also take advantage of the abundant supply of resources during the wet season, because they spend much more time feeding and

Adult male howler climbing through the trees: photo credited to webmaster@acguanacaste.ac.cr

 

 

foraging and less time resting compared to their dry season activity. (Mittermeier 1999).

Nonsocial exploration for infants consisted of actively crawling on the mother's body or in the trees. Exploration was done with tactile sense (fingering stuff), visual senses (visually tracking some moving object), oral senses (feeling stuff around in mouth). The infant would cling to the mother passively while the mother was mobile, yet would branch off during resting periods about 1-3 m away from their mother and explore. Infants are clumsy when exploring but very careful when clinging to mother (its very rare for one to fall off the mother). Infants will make calls if it lost from its mother. Investigativesocial contact for infants involves infants occasionally reaching out from mother's back to touch other infants on their mother's back. Yet, they showed very little mutual interest in social contact. Contact play and wrestling occurs in older infants or juveniles when players assume face to face position and push, tug or grapple each other from feet position or hanging with their tails. No vocalizations are made during these bouts, unless infant feels threatened and whimpers to get other howler off.

Infant howler: photo credited to Estrada et al.

 

 

In most troops, play only consisted of about 5-15 minutes of the infant's total day. And the arrival of an adult immediately eliminated play activities. Non-contact and Chasing Play was the most extreme form of play because it could result in injury. When contact became too rough for infants, they would withdraw, and neither would continue to aggravate the other. Yet, chases did occur but only lasted for about 0.5 to 3 meters and most did not exceed 2 m. Chases were most common when lots of animals were together. Older howlers engage in less play because they need to conserve energy and their digestive process is very complex and needs a lot of time to work (Baldwin and Baldwin, 1978).

The proportions for the activity pattern of the howler monkey are reported at 72.7 % resting, 16.8 % feeding, and 10.5 % traveling (1999). The most intense foraging occurs directly after awakening, when they move around the general area of the sleeping tree (another reason why howler's pick resourceful sleeping sites). After this activity, a nap or period of resting usually follows. Alouatta palliata are travel minimizes because the food they eat is not nutritional enough for them to remain active for long periods of time. They minimize travel to minimize the cost of foraging (cited in Broekema, 1999).

Grooming

Mantled howlers rarely groom one another. Only a marginal portion of the day is allotted for social interactions and very little grooming takes place. If grooming does occur, it is usually a female howler grooming a dominant male. In any case, a subordinate in the troop most likely grooms a dominant individual. Yet, in rare instance, some groups of howlers devote more time and energy to grooming behaviors, and these animals use these grooming behaviors to strengthen their bonds with one another (Jones 1979). These are all selfish behaviors, because the subordinates performing the grooming are trying to persuade the dominant individuals in the group to help them in some way.

Communication

Alouatta palliata use various forms of scent marking by rubbing their urine and body parts on tree branches. This primarily occurs with adult males during stressful situations. Milton (1975) observed howlers urinating on their tails and palms and rubbing the urine on their body. Milton concluded that this might serve as a marking system when howlers travel through the canopy. Since they need to conserve energy, they mark the shortest route to a certain destination in their home range so others can follow it later. She also thinks that the urine allows males to know when females are coming into estrus (1975).

Adult male howler roaring: photo credited to Dr. Linda Winkler

The most important form of communication for howlers is the renowned roar they rub out of their throats in the early morning. This territorial roar, often referred to as the "dawn chorus," allows howlers to let other troops of howlers know their location. It also serves as a warning signal to these other howlers to not crossover into their home range. Sometimes these roars will be given during the day to round up the troop for more travel. The female roar is much softer than the male roar. Roaring by females is usually to ward off outside females or simply to exert dominance over the other females in the troop. When males and females roar together, it serves as a bond strengthening activity. Although most of the howling is performed at dawn, some howling occurs in the late afternoon or night and probably serves the same purpose of communicating to other howlers not to invade area (Whitehead, 1989). Cuaron (1995) witnessed something interesting concerning a solitary howler male under pursuit and not using his roar to ward off the other howler males. Cuaron concluded that howling is something strictly defensive for the howlers, since solitary males do not have a group to defend, but roam around freely looking for a group (1995).

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