Western Lowland Gorilla (Gorilla gorilla gorilla)

The Western Lowland Gorilla is the nominate subspecies of the Western Gorillas found in Cameroon and other parts of Central Africa. It is also the smallest of the four subspecies.

This type of gorilla has black skin and coarse black hair except for the bare face, ears, hands, and feet. Notably, Snowflake, the unique albino gorilla from Equatorial Guinea, hailed from this species. Taken as a youngster to the Barcelona Zoo in 1966, Snowflake's pale form intrigued the world. 

Contrary to previous beliefs that gorillas were non-territorial, studies have shown that their neighbors' locations influence their movements. They demonstrate a preference against feeding in areas visited by another group the same day, indicating a more nuanced territorial behavior4.

Interestingly, Western Lowland Gorillas show signs of tool use. A recorded instance in 2009 reveals a gorilla using a stick to gauge water depth while another used a bucket to collect water at Buffalo Zoological Gardens. This display of spontaneous tool utilization for drinking, particularly among younger females, provides a unique glimpse into gorilla cognition. 

Lastly, a serious concern with western lowland gorillas is their link to zoonotic diseases. Scientists believe them to be one of the sources of HIV/AIDS transmission. This is attributed to the Simian immunodeficiency virus (SIV) in gorillas, which surprisingly resembles a strain present in HIV-1.

Cross River Gorilla (Gorilla gorilla diehli)

Cross River Gorillas live in the border zone between Nigeria and Cameroon. The habitat is broadleaf forests with altitudes ranging from 328 feet to 6,683 feet.

In physical attributes, it bears shorter skulls, smaller cranial vaults, and smaller palates than the previous type of gorilla subspecies. However, size and limb length match closely. One distinctive aspect of Cross River gorillas is their shorter hands and larger opposability index.

In general, wild gorillas are not dangerous. However, they can show aggression when disturbed. Behavioral differences emerged in a three-year study at Kagwene Mountain, Cameroon. The Cross River gorillas threw fistfuls of grass3, branches, and stones. Researchers concluded this action is a learned response to local conditions.

The nesting habits of Cross River gorillas also differ by environmental conditions. During the dry period, most nests are found on the ground, but in the wet season, they opt for tree-high nests to shield them from the rain. 

They also make more day nests during the rainy season and reuse old nesting sites around 35% of the time. These patterns highlight the adaptive and intelligent characteristics of this incredible gorilla subspecies.

Eastern Lowland Gorilla (Gorilla beringei graueri)

Eastern Lowland Gorillas, also known as Grauer's Gorillas, live in the eastern Democratic Republic of the Congo home, specifically two national parks and surrounding forests. It thrives in the broadest range of altitudes, from lowland tropical forests to mountainous terrains.

They are also the largest gorilla subspecies, earning the rank of the heftiest living primate. Its appearance resembles a mountain gorilla with a jet-black coat, albeit shorter on the head and body.

Despite seasonal changes, Eastern Lowland Gorillas exhibit steady nesting patterns1. However, habitats differ between adults and young, with immatures favoring tree nests, indicating vulnerability. Moreover, the absence of an alpha silverback substantively influences nesting choice, signifying the male's critical protective role.

However, our knowledge of its social patterns, history, and ecological role is currently limited. This unfortunate situation stems largely from ongoing civil unrest in the Democratic Republic of the Congo, which hinders consistent research efforts. This circumstance underscores the cross-link between human-generated strife and our ability to study and protect crucial elements of biodiversity.

Mountain Gorilla (Gorilla beringei beringei)

The Mountain Gorilla endures high altitudes within the cloud forests of three national parks, spanning across the Virunga volcanic mountains and extending its reach into one of Uganda's national parks. This species inhabits zones climbing up to 7,200 to 14,100 feet.

Unlike other types of gorillas, the Mountain Gorilla possesses thicker, longer fur designed to withstand colder climates inherent in its environment. 

Despite being smaller than the Eastern Lowland Gorilla, adult male gorillas demonstrate distinctive bony crests atop and at the back of their skulls, giving them a conical appearance. These crests also anchor their powerful jaw muscles.

Starting in 1967, Dian Fossey dedicated 18 years to a detailed study of mountain gorillas. She brought new findings to light, implemented accurate counts, and introduced helpful conservation methods, like anti-poaching patrols. Her work continues through the Dian Fossey Gorilla Fund International, protecting Virunga's mountain gorillas.

Similarities in genetic makeup to humans expose mountain gorillas to human diseases2. An immune system ill-developed against such diseases results in respiratory infections, accounting for approximately 20% of sudden deaths among these gorillas.

Gorilla Conservation Status

As per the latest International Union for Conservation of Nature (IUCN) assessments, Gorilla conservation status exposes some alarming trends. Three of four sub-species of gorillas have been declared critically endangered with declining gorilla populations.

In 2013, Western Lowland Gorillas numbered 361,919, which is currently shrinking by roughly 2.7% annually. By estimates, this downward trend could result in over an 80% population decline across just three generations.

Cross River gorillas, known to us since the early 20th century, only received notable attention in the late '80s. Now, merely 100-250 mature individuals remain in the wild.

Grauer's Gorillas, valued at just 3,800, have suffered a drastic 77% population decrease since 1994.

Mountain Gorillas are not entirely clear despite their reclassification from critically endangered to endangered species5. While recent counts estimate at least 1,004 individuals, legal and illegal human intrusion into their habitats could threaten them again.

Regardless of the varied threat levels, all gorilla subspecies face common dangers. A relentless onslaught of habitat destruction, hunting, and diseases such as the ebola virus poses significant risks. In response, conservation efforts have been deployed to counteract these threats.