Species (Gorilla gorilla)
ecology and behavior of both western gorilla subspecies are poorly
known compared to the well-studied mountain gorillas (Gorilla
beringei beringei). Though western lowland gorillas have been
the subject of much research in captivity (e.g., Lukas et al., 1999;
Mallavarapu et al., 2006), field studies of these animals have been
limited and began only in the 1980's for western lowland gorillas
(e.g. Tutin and Fernandez 1984, 1985) and the mid 1990's for Cross
River gorillas (McFarland 2007). Unlike the mountain gorillas, habituation
(desensitizing them to the presence of people) of western gorillas
has proven extremely difficult. As a result, much of the research
on populations of these gorillas has been on unhabituated animals
from viewing platforms (e.g., Remis 1999; Magliocca et al 1999;
Parnell 2002), or using indirect methods such as DNA analysis (e.g.,
Bradley et al. 2004; Bergl and Vigilant 2007) or examination of
fecal samples and feeding remains (e.g., Goldsmith 1999).
lowland gorillas inhabit primarily primary and secondary lowland
forest, swamp forest and, in some areas, submontane forest. Many
western lowland populations also frequently visit "bais":
large swampy clearings in the forest where they feed on plants rich
in protein and minerals. Cross River gorillas utilize a wide variety
of habitats ranging from lowland rainforest at around 100m in elevation
to montane rainforest and grasslands at over 2,000m. Probably due
to the greater diversity of foods available in these habitats compared
to those of the mountain gorilla, western gorilla diets include
large amounts of fruit (Rogers et al., 2004). The Cross River gorilla
has a diet particularly high in fruit that is also highly seasonal,
varying considerably between the dry and rainy seasons.
western gorilla subspecies have larger home ranges and travel further
over the course of a day than mountain gorillas (Remis 1997; Bermejo
2004; Doran et al., 2004; McFarland 2007). These larger home ranges
and daily travel distances may be related to the more diverse (and
seasonal in the case of the Cross River gorilla) diets of western
gorillas. The large amount of fruit in their diets may also explain
the generally smaller size of western gorilla social groups (Magliocca
et al.,1999; Doran and McNeilage 2001). Smaller group size may help
to avoid competition for food resources. Though social groups of
western gorillas are generally smaller than those of mountain gorillas,
groups of 20 or more individuals have occasionally been recorded
for both western lowland (e.g., Carroll 1998; Magliocca et al. 1999)
and Cross River (Oates et al., 2003; Bergl unpublished data) subspecies.
- Text by Richard Bergl, Ph.D.
and Kimani, G.g. gorilla, Zoo New England
(photo by Ellen Slotnick)
Species (Gorilla beringei)
of what is known about gorilla ecology and behavior is derived from
the long-term studies of the Virunga mountain gorillas conducted
at the Karisoke Research Center. Established in 1967 by Dr. Dian
Fossey, Karisoke has hosted scientists from around the world who
have studied topics including maternal behavior, infant development,
general social behavior, reproductive strategies, feeding behavior,
habitat use and life history decisions (see Robbins et al., 2001;
The Dian Fossey
Gorilla Fund International, www.gorillafund.org). As data on
other populations of gorillas have become available, it has become
evident that mountain gorillas occupy an 'ecological extreme' that
has considerable implications for their behavior and social organization.
Essentially, mountain gorillas live in a salad bowl of highly nutritious,
locally abundant vegetation. Such high food availability results
in smaller home ranges, shorter day journey lengths, and larger
group sizes than their western counterparts (Doran and McNeilage,
2001). It may also affect reproduction patterns and group composition.
Mountain gorillas wean their infants a year earlier than western
gorillas (Nowell and Fletcher, 2007) and have a much higher prevalence
of multi-male groups (Weber and Vedder, 1983; Gray et al., 2005).
mountain gorillas and Grauer's gorillas live at slightly lower altitudes
than Virunga mountain gorillas. As a result, fruit is an important
part of their diets, and, probably as a result, they have larger
home and day ranges (Doran and McNeilage, 2001; Yamagiwa et al.,
on mountain gorilla behavior and ecology is ongoing in both the
Virunga and Bwindi populations. Visit www.gorillafund.org
for information on the research activities of the Karisoke Research
Center and www.itfc.org
for information about research on the Bwindi population from the
Institute of Tropical
on Grauer's gorillas are currently focused on obtaining accurate
estimates of population density and distribution. These studies
are being carried out by the Union of Associations for Conservation
of Gorillas and for Development in the East Democratic Republic
of the Congo (UGADEC) and The
Dian Fossey Gorilla Fund International.
- Text by Tara S. Stoinski, Ph.D.
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