February 18, 2014

Should humans have a mating season every 7 years?

Orangutans belong to the order primates, which is the group of animals including monkeys, apes and humans. Since the primates include ourselves and all of our closest relatives, it makes sense if we learn a few things from them.

The orangutan, this beautiful red ape is unique in many ways: It is the only great ape in Asia - indeed, the only one outside Africa and it is the most arboreal and least sociable of all the great apes. 

They are a source of major fascination because of being like humans and highly intelligent, at the same time being big but extremely strong.

Seeing orangutans in the wild can be a thrill. But they are extremely difficult to see in the wild as they occur at low densities; their forests, in the two islands of Sumatra and Borneo, are often either in deep swamp or up steep, rugged hills. Many of the forests where they occur are also remote, inaccessible, and often not open to the public.

For a second best, I visited the Semonggoh and Matang Wildlife Centre in Sarawak, in the island of Borneo, Malaysia.

The orangutans are in the book of record for good reasons.

They are the largest tree-dwelling animal in the world and one of the largest and most intelligent primates. They are amazingly powerful for their size although their diet consists mainly of fruit. 

They are exceptionally agile in forest partly due to having mobile hip joints and also opposable toes on the foot, which effectively give the animals four hands. They can manipulate objects almost as well with their feet as they can with their hands. They can move through trees and hang upside down from branches using just their feet to support their whole weight.

The orangutans are predominantly fruit-eaters. They are the largest animals in the world whose diet mainly comprises of fruit. Wild figs make up about a third of their total diet. A single orangutan feeds on more than a hundred different types of fruit in a year. Many fruits are sweet and succulent, such as mangoes, providing lots of energy. Others are rich in oils and protein such as durian.

At times when fruits are scarce, they eat other food such as twigs, bark, honey and some animals’ foods such as termites, ants, bees, birds' eggs and small lizards. They are the only animals in the forest that can pull part of the tough, thick bark from a tree, with a combination of hands, feet and teeth.

Orangutans need to eat vast quantities of fruits. This means that almost half of an orangutan's day is spent in extracting food and eating it.

The orangutans' intelligence is not surprising, given their ability to remember and even predict the location of food trees in a complex, diverse rain forest.

Orangutans are mostly solitary, which is rare since primates usually have rich social lives.  It was suggested that being solitary is a necessity for orangutans since their caloric needs are so large they cannot share.  Also, no large predators except for humans threaten orangutans so they do not need large social groups to protect themselves.

Orangutans have a reproductive cycle that is similar to humans.  A female orangutan's reproductive stage lasts roughly nine months. Female orangutans are also similar to human females because they both do not show external signs of menstruation and their reproductive cycles last roughly 30 days. 

But a female orangutan will give birth every 6 to 8 years.  This is amazingly infrequent; it is the slowest breeding rate of any primate, and amongst the slowest of any mammal. 

The reproductive process for female orangutans is very taxing since feeding herself is already a daunting task without having to take care of an infant; she travels anywhere from 50 meters to 1,000 meters in one day to look for fruits to eat.

Female orangutan become sexually mature at seven or eight years old, but males do not become fully socially and sexually mature until they are 13 to 15 years old or more. Even then, males will not develop their full adult male attributes of face flanges and throat sacs if they are in the presence of a dominant adult male, so they might have to wait even longer until they are fully mature adult males.

Males are twice as big as females; their average weights are 75 kg and 40 kg respectively. In zoos both become over weight and some males reach 200 kg because of over eating and lack of exercise.  In the wild, orangutan rarely stand upright but if they did males can reach 1.5 m in height – but their arm span is 2.25 m. 

Young orangutans spend much of their time in play. Mothers will be within constant contact of their offspring for the first year of life and stay within contact with their young for its first 7 years of life. 

Only when the young orangutan has a new sibling, it does not stay close to its mother and gradually becomes more independent.