The Gorillas of the Ebo Forest, Cameroon
Cameroon is a particularly important habitat country for gorillas since
it has two subspecies, separated by several hundred kilometers of forest
and the Sanaga River. Gorilla gorilla gorilla, or the western lowland
gorilla, was, until recently, thought to be restricted to areas south
of the Sanaga River, and has been hard hit by hunting for at least the
past 100 years. This southern region of Cameroon has also been affected
by commercial logging activities for decades, and most of the few remaining
populations are increasingly under threat. Gorilla gorilla diehli,
or the Cross River gorilla, is even more endangered, with numbers estimated
at around 250 split into at least nine isolated populations north of the
Sanaga River along the Cameroon-Nigeria border (Oates et al. 2003).
In late 2002 a gorilla population separated from the lowland gorilla population
south of the Sanaga River by around 100 km (distance to the Sanaga), and
from the Cross River gorilla population by ca. 200 km, was "discovered"
in the Ebo forest, Littoral Province, by a field team of the Center
for Reproduction of Endangered Species, Zoological Society of San
Diego (CRES) and 7 gorillas were observed for almost two hours (Morgan
et al. 2003). The first suggestion that gorillas might occur within this
forest resulted from a four-day survey of Ebo by F. Dowsett-Lemaire and
R. J. Dowsett in 2001. They noted 8 old gorilla nests, but no direct sightings
or other confirmation of the existence of gorillas in this forest was
obtained. Most recently, in March 2004, the CRES field team observed a
lone male gorilla for 15 minutes.
One interesting point worth noting about the gorillas in Ebo is their
propensity to nest high in the trees. During our gorilla encounter in
late 2002, we have reported that all 6 day nests were arboreal, constructed
at between 15 m to over 30 m above the ground (Morgan et al. 2003). At
the site of our most recent sighting in March 2004, 4 night nests were
discovered, all over 18 m from the ground. Possible reasons for the low
frequency of ground nests elsewhere have included risk of disturbance
(e.g. by elephants) or a lack of suitable ground nesting material. In
Ebo, the abundance of large rocks and boulders throughout the area may
be an added incentive to build arboreal nests.
The discovery of the Ebo gorilla population raises important questions
as to the nature and role of zoogeographic barriers to speciation in this
region, as well as taxonomic affinities of this new population. Although
Ebo and the contiguous forest blocks are poorly known, the Ebo gorilla
population may represent a remnant of a previous distribution, extending
across the Sanaga River to the extant Cross River/Takamanda population.
The majority of the intervening populations may have been extirpated by
a high degree of human disturbance in Cameroon over at least the last
century. Both the Cross River populations and this newly discovered population
are currently restricted to higher elevation and inaccessible forest,
which probably accounts for their continued existence. Most recent evidence
indicates that there are no fully reliable methods for obtaining high-quality
DNA from non-invasive samples in gorillas (Thalmann et al. 2004), but
we are collecting both hair and faecal samples wherever possible.
The Ebo forest is one of the largest single areas of lowland and montane
forests in Cameroon, covering 1,424 km² of semi-deciduous and evergreen
forest in Littoral Province. Topographically it consists of a series of
hills and mountains with steep slopes and deep valleys, with an altitudinal
range from less than 200 m to over 1,200 m. The gorilla population appears
to be centered on a series of steep mountains close to the abandoned village
of Bekob. Although today the forest is devoid of permanent habitation,
until the 1960s several villages peppered Ebo, including Bekob, which
was home to a German missionary doctor who ran a small hospital. The tribal
wars during this period caused widespread unrest, and the enclaved villages
were abandoned, with the inhabitants creating new settlements or joining
existing villages that today run along the northern edge of the Ebo forest.
The Ebo forest is unusual in Cameroon, because it is currently thinly
populated, the challenging topography has limited the potential for commercial
logging and it harbors a significant and diverse assemblage of large mammals.
We found extensive evidence of drills (Mandrillus leucophaeus),
one of the most endangered primate species in Africa, in Ebo during recent
field expeditions, and managed to make a number of direct observations.
Chimpanzee populations in Cameroon are more numerous than gorillas, but
are still under intense hunting pressure in almost all areas. Gonder et
al. (1997) proposed that there are two subspecies of chimpanzee in Cameroon
- Pan troglodytes troglodytes south of the Sanaga river and Pan
troglodytes vellerosus to the north. Several populations of this northerly
subspecies, first described as long ago as 1862 but only recently recognised
as a valid subspecies, have become extinct in the wild less than a decade
after first being documented, but in Ebo populations are still extensive
and we regularly hear chimpanzees during our fieldwork.
In addition to gorillas, chimpanzees and drills, there are 8 other diurnal
primate species at Ebo. Both Preuss' red colobus (Piliocolobus preussi)
and Preuss' guenon (Cercopithecus preussi) are endangered species,
yet both appear to be present in good numbers at Ebo. The latter species
is very sensitive to hunting and has already disappeared from a number
of localities elsewhere in Cameroon. In addition, the mona monkey (Cercopithecus
mona), putty-nose monkey (C. nictitans), crowned monkey (C.
pogonias) and the red-eared monkey (C. erythrotis) have been
observed, together with the red-capped mangabey, Cercocebus torquatus
and guereza colobus, Colobus guereza.
Forest elephants (Loxodonta africana cyclotis) still occur in Ebo,
though they have been hunted out in most of the surrounding areas. Forest
buffalo (Syncerus caffer nanus), red river hog (Potamochoerus
porcus), sitatunga (Tragelaphus spekei), bushbuck (T. scriptus)
and several duiker species are also present.
The Ebo forest, together with two further areas - Makombe and Nlona-ko
- were designated "Proposed Protected Areas" by the Government
of Cameroon in January 2003, with the gazettement and demarcation process
due to commence in late 2004. This process will be undertaken by a team
under technical supervision from CRES Cameroon and WWF Coastal Forests
Program. In May 2004 CRES Cameroon will establish a permanent field presence
at Ebo in order to have a base from which to study the gorilla population.
Field studies are also important since the ape populations have an additional
degree of protection because researchers will maintain a monitoring presence
in the field as well as enabling the constituency of public interest and
support, both in Cameroon and elsewhere.
We also plan to conduct transect surveys throughout the Ebo forest to
assess the distribution and density of the gorillas, and will additionally
survey forest outside the present limits of the proposed protected area
to ascertain whether the current boundaries will be sufficient to protect
the Ebo gorillas.
There are several communities situated around the Ebo forest, and the
impact of these populations on the forest has not yet been quantified
nor described systematically, but it is clear that human population density
is low.
Although hunting for the commercial bushmeat trade is likely to be important
in the villages to the south given the proximity of major towns such as
Douala, the mountainous terrain has restricted hunting within the central
area of Ebo. The small villages to the north seem to be sustained by bushmeat
extraction sold (mostly) locally. Given the parallel mountain ranges running
north-south throughout this region, with steep valleys and deep rivers,
hunters do not penetrate far in the area from either east nor west, and
so thanks largely to its topography, both the plants and animals of the
proposed Ebo protected area have been relatively spared the effects of
habitat destruction found elsewhere in Cameroon. We intend to start a
study of bushmeat offtake in villages and towns to the north of the Ebo
forest in mid-2004, which will entail close collaboration with Cameroonian
authorities.
Bethan Morgan
The Ebo gorilla population and the areas where
specimens of western lowland and Cross River gorillas were collected
Grateful thanks to the Government of Cameroon (DFAP-MINEF) for continued collaboration, and to the Margot Marsh Biodiversity Foundation and the Offield Family Foundation for financial support. Thanks also to our collaborators, WWF Coastal Forests Program and WCS Cameroon.
References
Gonder, M. K. et al. (1997) A new west African chimpanzee subspecies?
Nature 388:337.
Morgan, B. J. et al. (2003) Newly discovered gorilla population in the
Ebo forest. Littoral Province, Cameroon. International Journal of Primatology
24(5):1129-1137.
Oates, J. F. et al. (2003) The Cross River gorilla: Natural history and
status of a neglected and critically endangered subspecies. Pp. 472-497
in: Taylor, A. B. & Goldsmith, M. L. (eds.) Gorilla Biology: a multidisciplinary
approach. Cambridge (Cambridge University Press).
Thalmann, O. et al. (2004) Unreliable mtDNA data due to nuclear insertions:
a cautionary tale from analysis of humans and other great apes. Mol. Ecol.
13:321-335.
Dr. Bethan Morgan studied the ecology of forest
elephants in Gabon. Since 2002 she has held a postdoctoral fellowship
from the CRES field program in Cameroon, where she studies the ecology
of large mammals, particularly drills.