The Cross River gorilla (Gorilla gorilla diehli) is a subspecies of the western gorilla. It was named a new species in 1904 by Paul Matschie, a mammalian taxonomist working at the Humboldt University Zoological Museum in Berlin, but was not systematically surveyed of its populations until 1987.
Cross River gorilla is the most western and northern form of gorilla, and is restricted to the forested hills and mountains of the Cameroon-Nigeria border region at the headwaters of the Cross River. It is separated by about 300 km from the nearest population of western lowland gorillas and by around 250 km from the gorilla population in the Ebo Forest of Cameroon.
In 2007 IUCN (International Union for Conservation of Nature) labeled the Gorilla gorilla delhli as critically endangered.
The most recent surveys suggest that between 200 and 300 Cross River gorillas remain. Groups of these gorillas concentrate their activities in 11 localities across a 12,000 km² range, though recent field surveys confirmed the presence of gorillas outside of their known localities suggesting a wider distribution within this range. This distribution is supported by genetic research, which has found evidence that many Cross River gorilla localities continue to maintain contact through the occasional dispersal of individuals. In 2009, the Cross River gorilla was finally captured on professional video on a forested mountain in Cameroon.
Reasons for the extinction of the Cross River gorilla include: Overhunting, forest fires and loss of genetic diversity, due to their small population and even smaller grouping size (4-7 individuals) and fragmented population. In 2007 though, a Regional Action Plan for the Conservation of the Cross River Gorilla was established that included conducting further research of the Gorilla gorilla diehli, raising awareness and teaching the locals about conserving the forests and protecting the Cross River gorilla, and limiting eco-tourism which can have negative effects of the species.
When comparing the Cross River gorilla to western gorillas, they have noticeably smaller palates, smaller cranial vaults, and shorter skulls. The Cross River gorilla does not differ much in terms of body size or limb and bone length from western gorillas. However, measurements taken from a male suggest that they have shorter hands and feet and have a larger opposability index than western gorillas.
The Cross River gorilla, like many other gorilla species, prefer a dense forest habitat that is uninhabited by humans. Due to the Cross River gorilla’s body size they require large and diverse areas of the forest to meet their habitat requirements. Similar to most endangered primates, their natural habitat exists where humans are often occupying and using for natural resources. Forests that are inhabited by the Cross River gorilla vary in altitude from approximately 100m to 2,037m above sea level.
The habitats of the cross river gorilla are negatively affected by the drastic deforestation and fragmentation of the land. These unfortunate events leave the gorilla species with few options for survival. As a result of deforestation and fragmentation, there are drastic reductions in carrying capacity, in other words, the size of the territories these animals inhabit has been significantly reduced. Because the population of humans living in this area is high, the amount of resources available to the cross river gorillas’ is limited. Even though this decrease in the availability of land may appear to be a problem, research studies have found that an adequate amount of rainforest still remains that is suitable and comfortable for this species.
If, however, human pressures and activities towards deforestation continue, these territories will continue to diminish and ultimately will not exist. Additional examples of human activity that threaten cross river gorillas and, of course, other species, are hunting, logging, agriculture, fuel wood harvesting, clearance of lands for plantation and exploitation of natural resources. Gorillas and other primates are only a small part of the larger ecosystem and thus, they rely on many aspects of their habitat for survival. Furthermore, also because of their body size, they lack ability to adapt to new environment and they have a rather slow reproductive rate. Even though there is somewhat of a limited research on cross river gorillas, there is enough to conclude that these animals are currently able to sustain survival. What is still under debate is the total number of cross river gorillas that exist.
The population of Cross River gorillas declined by 59% between the years 1995 and 2010, a greater decline over that period than any other subspecies of great ape. Apes such as the Cross River gorilla serve as indicators of problems in their environment and also help other species survive. The decline of this species started thirty years ago and has since continued to decline at an alarming rate. The danger of hunters has lead these creatures to fear humans and human contact, so sightings of the Cross River gorilla are rare.
While all western gorillas are Critically Endangered (in the case of the western lowland gorilla due in part to Ebola virus), the Cross River gorilla is the most endangered of the African apes. It is one of the world’s 25 most endangered primates according to the IUCN Primate Specialist Group. In the efforts to conserve other species, it has already been obvious to bring the scattered population together to prevent inbreeding. One problem with the scattered populations is that the Cross River gorillas are also surrounded by human populations that cause threats such as bushmeat hunting and habitat loss. Also, the protected regions causing the Cross River gorillas by the Nigeria-Cameroon border are close by to hunting regions causing the Cross River gorilla to have a more likely chance to go extinct. The Cross River gorilla is especially significant to the ecosystem because they are excellent seed dispersers for certain tropical plant species that would otherwise be extinct.