Moving about in the trees
Locomotion helps to distinguish a mammalian order from the others. Common examples are the bats and the whales. Similarly, one of the characteristics that marked out a single species of primates is the locomotor pattern. Consisting of 4 general types of locomotor behaviour, all primates can be categorized under one of its subtopic. For example, both the gelada and the squirrel monkey are quadrupeds. Although both move on all four limbs with its body parallel to the ground, they fall under different subcategories. The gelada spends much more of its time on the ground. Thus, unlike the spider monkey, their movement does not involve grasping with hands. The gelada is categorized under ‘ground running and walking’, whereas the spider monkey belongs to the subcategory ‘New World semibrachiation’. Another subcategory, besides ‘slow climbing’, is ‘branch running and walking’. A representative primate of such category is, including all other capuchin monkey families, is the squirrel monkey.
Squirrel monkeys are small, agile and curious New World monkeys that live in lower layers and edges of tall forests. The two species have two completely separate distributions. The common squirrel is found in most parts of the South American rainforest, and the red-backed squirrel monkey in Costa Rica and Panama. In large expanses of Amazonian forests, groups may contain several hundreds individuals. However, most groups avoid close contact with neighbouring groups. Subgroups never stay too long on one tree, but travel from tree to tree constantly. However, they would visit the same tree and return to it repeatedly. They prefer vegetation with many thin vines and branches. As they run and jump through the vegetation, they keep to the middle and lower levels of the forest. Occasionally, they use the ground to move about. They do climb trees to reach for fruits in treetops and are often associated with capuchin monkeys. They often travel with these monkeys. Squirrel monkeys arrive faster at local food trees by following the capuchins than if they search alone. Along the way, they hunt for insects and spiders. They move quadrupedally through the trees. Having thighs that are shorter relative to the lower leg, squirrel monkeys move by leaping. This allows more force to be developed in the jump. As part of the steps to adulthood, active plays in the trees gives young monkeys a chance to develop skills for running and jumping through trees. Skills such as wrestling and sparring are important if the monkeys ever have to flee from predators or respond quickly in emergencies.
Like the squirrel monkeys, spider monkeys move similarly, but they often sprawl quietly or hang motionless on branches, thus maybe difficult to spot. However, when disturbed, they may threaten a human by stamping and shaking vegetation, breaking dead branches and growling. As tree climbers, they also use their very flexible, prehensile tails as extra limbs. These versatile grasping organs easily support the animals’ whole weight. Having long arms and extra mobility in the shoulder joints, these monkeys sometimes hang upside down to feed near tips of branches, with all four limbs and tail grasping the branches for safety. Their hands are specially adapted to this type of movement. The thumb is non-functional, while the other 4 fingers serve as hooks for them to anchor themselves on branches. Despite being able to run on two legs on the ground, these monkeys spend most of their time in the crowns of trees and travel mainly by swinging. However, long-haired monkeys are observed never on the ground. Even while searching for food, they would come down to a minimum height of 12m (38ft). Foraging and feeding covers about a third of their period of activity. The rest of their time is spent on travelling. They travel no less than 1km (one-half mile) each day. Although spider monkeys are able to brachiate, only small Asian apes called gibbons can swing through trees faster.
Gibbons are the acrobats of the ape world. In fact, they are the only true brachiators among the apes. Their graceful, long-limbed bodies allow them to dangle from high branches and swing along rapidly through the rainforest canopy. The speed at which they can move through the treetops is remarkable. This ability enables gibbons to quickly retrieve temporary food resources and better defend their territorial boundaries. When they leap across gaps, they look like they are flying. They swing by holding on to the branch with first one arm, then the other; their long fingers hook over the branches. Unlike a quadruped, gibbons can suspend itself under a branch on one arm for up to 20 minutes. In this position, the gibbon can collect various fruits and plant parts growing on branches beneath it by using its free hand. Their long arms can also be extended to counterbalance bipedal steps taken over the tops of large branches, and more rarely, on the ground. In fact, they are more efficient at bipedal walking than great apes. This is because gibbons cannot walk on all fours. Their arms are very much longer than their legs. Instead, they walk upright with their arms above their heads, to keep them out of the way, looking like tightrope walkers.
The largest ape on the tree, the orang utan, on the other hand are obviously much slower in their movement. Due to their heavy weight they climb around the trees slowly and with much care. Like many other apes, their legs are just like hands and all four are used to hold onto the branches. Unlike the gibbons, it is impossible for them to leap from branch to branch. Instead using their long arms, they reach out to the next nearest branch and hold on to it. Also another method, making full use of their weight, orang utans are seen to rock the trees they are in to bend it so that they are able to grab hold of the branches of other trees nearby. For many males, their weights are too heavy to be supported by the trees and thus they spend more time on the ground.