Батыс горилласының сирек кездесетін түрі - Кросс-Ривер горилласы

Subspecies of the western gorilla

The Cross River gorilla (Gorilla gorilla diehli) is a critically endangered subspecies of the western gorilla (Gorilla 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 its populations were not systematically surveyed until 1987. In 2009, the Cross River gorilla was finally captured on professional video on a forested mountain in Cameroon.

A study published in 2007 in the American Journal of Primatology announced the discovery of the subspecies fighting back against possible threats from humans. They "found several instances of gorillas throwing sticks and clumps of grass". This is unusual. When encountered by humans, gorillas usually flee and rarely charge. Cross River gorillas have certain nesting behaviors (i. e. mean nest group size, style of the nest, location of the nest, and nest reuse patterns) that depend on things such as their current habitat, climate, food source availability and risk of attack or vulnerability. According to research done on the Cross River gorillas living in the Kagwene Gorilla Sanctuary, there is a high correlation between whether a nest is constructed on the ground or in a tree and the season. From April up until November, Cross River gorillas are more likely to build their nests within a tree, and from November on they are more likely to build it on the ground. Overall, it was found that more nests built at night were built on the ground as opposed to in trees. This species is also more likely to construct nests during the wet season than the dry season, as well as construct more arboreal nests in the wet season. It was found that day nest construction was more common, especially in the wet season. Reuse of nesting sites was also found to be common, although it did not have any relation to the season. And, their mean nest group size is from four to seven individuals. Although, nest group size varies depending on the location of the species. The Cross River gorilla's diet consists largely of fruit, herbaceous vegetation, liana, and tree bark. Much like their nesting habits, what they eat is contingent on the season. Cross River gorillas eat more liana and tree bark throughout the year, and less fruit during dry periods of scarcity.

The nesting behavior of the Cross River gorilla was influenced by the environmental conditions, such as the climate, predation, herbaceous vegetation, absence of suitable nest building materials and seasonal fruits nearby. The gorillas did portray certain nesting habits like mean nest group sizes, size and type of nest created, as well as the reusing of certain nesting location nearby seasonal food sources. In Sunderland Groves research on the nesting behavior of G. g. diehli at Kagwene Mountain they discovered that the nesting locations, whether on the ground or arboreal, were greatly influenced by the current season. During the dry season most of the nests were made on the ground, yet during the wet season the majority of the nests were made high in the trees, to provide protection from the rain. It was also found that the gorillas created more day nest during the wet season and reused nesting sites about 35% of the time. It was also found that the mean group size was 4–7 individual, yet the mean nest size at the sites was 12.4 nests and the most frequent number of nests was 13, showing some gorillas may have made multiple nests. The researchers also found nest sites with up to 26 nests, showing that sometimes multiple groups would nest together.

The Cross River gorilla at the Kagwene Mountain in Cameroon has been observed using tools and it seems to be unique to the population in this region. They have been observed in three separate cases, in which they threw grass at the researchers, a detached branch and in a third case, in which an encounter with a man who threw rocks at them led them to throw back fistfuls of grass. All the encounters had the gorillas in the group observe the researchers and react to their presence with vocalizations then led to calm behavior in the parts of the gorillas and finally an approach by the male gorillas and the throwing of grass at the researcher. The researchers have stated that this throwing behavior might have arisen due to human contact in the field and farms surrounding the mountain and the ambivalent nature of the gorillas is due to the surrounding people not hunting the gorillas due to the folklore about the gorillas. These locations cover a mostly continuous forest area of about from Afi Mountain to Kagwene Mountain according to the 2007 regional action plan for Cross River gorilla conservation. Researchers and conservationists also postulate that there is a possible outlying locality in the forests near Bechati in the southeast. Today it’s estimated that their total population area covers about .

Cross River gorillas reside in small populations split from other subpopulations of the species. They occupy roughly 14 apparently geographically separated areas in a landscape of approximately of rugged terrain spanning the Nigeria–Cameroon border region with population sizes estimated at 75–110 in Nigeria, and 125–185 in Cameroon. Other sources of degradation such as hunting posed a much higher threat but habitat loss is now posing a much bigger threat to the species and their survival. Populations reside in areas of undisturbed dense forest which is scarce due to human occupation or use for natural resources. The Takamanda National Park and the Kagwene Gorilla Sanctuary are where most of the surviving members reside. Nest distribution was clearly influenced by anthropogenic factors within the sanctuary, with the disturbed southern section of the park avoided.

The increased population of human inhabitants and the expansion of grasslands (due to human activity) has caused a fragmentation of the species into many subpopulations. Many factors (mostly related to human activity) contributed to the fragmentation of the population, including the expansion of farmland, human occupation, lack of accessible habitat and the sparsity of suitable or favorable habitat. Due to this isolation, gene flow has begun to slow and subpopulations are suffering from a lack of gene diversity which could mean a long term issue. A study conducted by researchers found that gene flow accompanied the divergence of western lowland and Cross River gorillas until just 400 or so years ago, which rather supports a scenario in which intensifying human activities may have increased the isolation of these ape populations. The recent decrease in the Cross River population is accordingly most likely attributable to increasing anthropogenic pressure over the last several hundred years. Despite laws preventing hunting, it still persists due to local consumption and trade to other countries. The laws are rarely effectively enforced, and due to state of the Cross River gorillas, any hunting has a large impact on the population and their survival. All hunting of the population is unsustainable. Cross River gorillas try to avoid nesting in grasslands and farms, which causes the remaining forest to become fragmented. When fragmentation occurs, this causes a decrease or even elimination of migration between subpopulations, and therefore causes more inbreeding within a single population. This led to the loss of genetic diversity. This has negative effects on the long term viability of population fragments, and by extension, the population as whole. Researchers use genetic methods to better understand the Cross River gorilla population. More specifically, certain loci within the genome were of major concern and they helped give the best insight into the subdivisions and dispersal of genetic variation across populations. Surveys suggest that the total population is about 300 individuals and is fragmented across about ten localities with limited reproductive contact. On top of this fragmentation, the Cross River gorilla is also threatened by hunting for bushmeat and for use of their bones for pseudoscientific medical purposes. Another threat to the Cross River gorilla is the harmful gorilla pet trade. To date, there is only one recorded Cross River gorilla in captivity, held at the de. The Cross River gorilla is critically endangered due to the combined threat of hunters and infection with Ebola. Even if the rate of Ebola mortality along with hunting was rebated, the promise of these gorillas making a fast recovery is unlikely. The reproduction rate of the Cross River gorilla is low and it is estimated that it will take 75 years for the population to fully recover. They are also threatened by loss of habitat due to mining, agriculture, and timber usage.

While all western gorillas are Critically Endangered (in the case of the western lowland gorilla due in part to the Ebola virus), the Cross River gorilla is the most endangered of the African apes. A 2014 survey estimated that less than 250 mature individuals were left in the wild. In efforts to conserve other species, it has already been determined that scattered populations should be brought together to prevent inbreeding. One problem with the scattered populations of Cross River gorillas is that they are surrounded by human populations that cause threats such as bushmeat hunting and habitat loss. Also, the protected habitats of Cross River gorillas along the Nigeria Cameroon border are close to hunting regions, which increases the threat of extinction. The Cross River gorilla is especially significant to the ecosystem because they are excellent seed dispersers for certain tropical plant species that would otherwise face extinction. In 2007, a survey was conducted in 5 villages in the aim of assessing taboos against hunting and eating these endangered species. In the Lebialem division of Cameroon, 86% of the population were in favour of the conservation of these species, seeing them as important morphological counterparts to humans which, in the case of their dying out, would cause the demise of their human totemic counterparts. One reason for the decline of cross river gorillas was believed to be the decline of adhering to these totemic practices among younger people in the 18 to 25 year age range. Regardless, this taboo is still in place and it still strongly discourages hunting of those endangered species. These totemic traditions are believed to be critical to the species' continued survival and well being. The recurrent revival of these beliefs and practices are seen was a way to reinforce the conservation of these species, especially in the absence of real law enforcement due to a lack of governance. While this could also foster support from different villages and communities, and preserve their culture, care must be taken when selecting these practices as some could encourage their killing. Largely because of many taboos, in the past 15 years, there has not been any Cross River gorilla hunting incidents. The presence of a taboo prohibiting their persecution has been considered an extremely successful local conservation strategy. A workshop for the conservation of the Cross River gorilla was organized by the Wildlife Conservation Society and the Nigerian Conservation Foundation was held in Nigeria in April 2001. The overall goal of the workshop was to enhance the species’ chance for survival because of its rare and distinct features from other western gorillas. The most important outcomes of the workshop were a list of improvements recommended to save the species and also establishing the need for regular meetings between the governments and conservation groups of Cameroon and Nigeria to achieve maximum efficiency in their conservation efforts. In 2008, the government of Cameroon created the Takamanda National Park on the border of Nigeria and Cameroon as an attempt to protect these gorillas. The park now forms part of an important trans boundary protected area with Nigeria’s Cross River National Park, safeguarding an estimated 115 gorillas — a third of the Cross River gorilla population — along with other rare species. The hope is that the gorillas should be able to move between the Takamanda reserve in Cameroon over the border to Nigeria's Cross River National Park. The Kagwene Gorilla Sanctuary was created by the Cameroonian government on April 3, 2008 as part of the IUCN’s Cross River gorilla action plan. It protects 19.44 km2 of land, and is located between the forests of Mbulu and Nijikwa in western Cameroon. It consists of rugged, mountainous terrain and represents the highest altitudinal extent of the Cross River gorilla's distribution, with the highest point at above sea level. Only about half of its land is a prime gorilla habitat, while the rest includes grassland or cultivation not suitable for the species. Due to its sanctuary status, it was expected to be provided with a conservator and eco guards to enforce wildlife laws within its perimeters.