Sunday, February 26, 2012

Territorial Behavior

Gorillas are highly social, relatively non-territorial and live in groups (called troops) that usually consist of 1-4 adult males, some juvenile males, and several young and adult females.  The oldest and strongest adult male (called the silverback) is usually the dominant one of the troop and has exclusive breeding rights with the females.  Adolescent females transfer to a different troop once they reach about eight years of age. Generally, the first troop in which the female produces offspring becomes her permanent troop.  A female's status is usually determined by the earliness of her entry into the troop.  For instance, latecomers do not get as many benefits, which include protection of offspring by the dominant silverback.  For this reason, females do not have strong relationships with each other because they are constantly fighting to be closest to the silverback in order to receive the most attention and protection.

Adolescent males, on the other hand, usually remain in the troop until they can leave and establish a new troop on their own as the silverback.  Troop populations range from 2- 12 individuals, with 9 being the average size.  The silverback is typically the most aggressive member of the troop because he is the one who must provide protection and security.  He also makes all of the group decisions, settles disputes between members, and gets the majority of the group's food.

Although gorillas typically aren't aggressive, they do exhibit territorial behavior by standing upright on their bottom two legs and pounding their chests in order to intimidate whatever threat they have been given.  These gestures, however, are more for show and aren't usually violent.  These instances can come about when two silverbacks of different troops meet, when two males are fighting over a female that they want to mate with, or when a younger male is challenging the silverback for dominance of the troop.  However, in stable troops these acts of violence and aggression are very rare.

At dusk, gorillas settle down for the night in nests made of vegetation that is shoved around them.  These nests are initially made by bending soft trees, breaking bamboo sticks, and taking large leaves from other types of trees to be used as a blanket to shield from the cold.  Mothers like to find a comfortable spot in the nest where their backs can be supported so that they can breast feed and cuddle their babies throughout the night. 


Sunday, February 19, 2012

Eating and Foraging Behavior

Gorillas’ eating behavior varies a bit depending on the subspecies, although all of them are predominantly herbivores. While the Eastern lowland gorilla eats predominantly plants (104 species), the Western lowland gorilla’s diet is composed of fruit, leaves, seeds, termites and caterpillars. The Mountain gorilla also eats a large variety of plants (142 different types) along with fruit, ants, and snails. All of the vegetation that gorillas eat has relatively low nutritional quality, which means that they must eat large quantities of everything. An adult male can consume approximately 40 to 50 pounds of foliage per day. They also rarely drink water because of the natural morning dew on the vegetation. Sometimes they also use the hair on the backs of their hands to “absorb moisture and then suck it,” (
            Gorillas are also very selective when choosing what to eat. They never consume a whole plant, but instead will only forage for the leaves, pith, stalk, or roots. They also have extremely supple lips and hand agility, which assists them in only consuming the specific parts of they plant that they want. Gorillas’ incredible strength also allows them to be picky with what they eat, because they could break apart a whole tree just to get to the interior pith.

Uganda Mountain Gorillas specifically spend most of 60% of their time either eating or foraging, and the remaining 40% relaxing. They may feed as their moving, but will usually pick a quiet open area to spread out and eat until they are full. Most gorillas do this as well in the wild.


Sunday, February 12, 2012

Introducing, Gorillas!

Evolutionary Background, Close Relatives, and Taxonomy

Gorillas are fascinating creatures because they are so like humans, yet still obviously have many very different qualities.  Both humans and gorillas share a common ancestor which was some sort of primate millions of years ago, however somewhere down the line the species diverged into two separate lineages.  One of these ultimately evolved into gorillas and chimpanzees, while the other evolved into humans.  Researchers believe that Gorillas began to differentiate from other apes and monkeys because they began to evolve into a larger and stronger species, which in turn caused a loss of agility and the gradual loss of a tail because their bodies eventually became too heavy to swing from trees. Instead, they began to swing with their powerful arms, which is why their arms are longer and stronger than their legs.  These strong arms also help for balance, and although they are able to stand and walk in an upright position, they are more comfortable on all fours with their knuckles being the point of balance.

The taxonomy of the Gorilla is as follows:
Kingdom: Anamalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Genus: Gorilla
Species: Gorilla and Beringei

Gorilla scientific classification has been divided into three subspecies based on where each is geographically located in Africa. The Western Lowland Gorilla (Gorilla gorilla gorilla) is the smallest of all three subspecies.  These gorillas typically live in the tropical forests of West Africa, and are the most common in zoos.  The Eastern Lowland Gorilla (Gorilla gorilla graueri) is slightly larger in size and typically resides in the rain forests of central Africa.  Finally, the Mountain Gorilla (Gorilla gorilla beringei) is the largest and rarest of all the subspecies.  These are naturally found in the Virunga Volcano range of Africa, and have darker coloring than the other subspecies because of the high altitudes in which they live.

It is very common to confuse apes with monkeys because the two words are often (wrongly) used interchangeably.  However, I would like to try and clarify a distinction between the two.  Gorillas are classified as apes, while others, like baboons for example, are classified as monkeys.  The main detail that differentiates apes from monkeys is that apes do not have tails while monkeys do.  Also, apes typically having larger body sizes and weights, as well as more of an upright body position.  Great apes also tend to be more ground-dwelling than monkeys who are typically more tree-dwelling.  This distinction has led to many evolutionary changes in the muscle and skeletal structure of the arms of apes because they are not as adapted to things like swinging from trees as monkeys are.  So, while gorillas indeed appear to be very similar to their other primate relatives, it is important to keep in mind the details and characteristics that separate them as apes from monkeys.

Fun Fact: Humans are more closely related to chimpanzees and gorillas than either of them are to orangutans!