Ecology of the Zanzibar red colobus monkey, Colobus badius kirkii (Gray, 1 968), in comparison with other red colobines - Biogeography and Ecology of the Rain Forests of Eastern Africa - page 259

less total phenolics and condensed tannins, than
blades (Mturi, 1991). This chemisry of leaf
peioles may have facilitated the high specialisa-
tion for leaf peioles seen in . b. go ronorum (see
Wasser, Chapter 13).
There is a variaion in the importance of dif-
fe rent plant parts to the diet among red colobus
subspecies. Red colobus living in habitats with
low tree species diversity - Fathala (Senegal),
Tana (Kenya) and Jozani (Zanzibar) - ate more
fruits and seeds and fewer mature leaves (includ-
ing peioles) than those in habitats with high tree
diversity - Kibale (Uganda), Gombe (Tanzania)
and Mwanihana (Tanzania). The switch from
folivory to frugivory may be an adaptaion to avoid
or reduce the intake of leaves that contain toic
secondary products and are generally indigestible,
especially when mature. If the leaves of trees in
the Tana, Jozani and Fathala habitats contain
generally high concentraions of toic secondary
compounds, the monkeys would be epected to
fe ed preferenially on acceptable nutrient-rich
items when present; even if these nutrient-rich
items also contain toic secondary compounds,
the additional nurients may offset the costs of
processing high toin concentrations (Moir &
Harris, 1962; Balch & Campling, 1965; Freeland
& Janzen, 1974; McKey, 1978). It may also be
that in habitats of lower ree species diversity,
mature leaves of only a few species were worth
exploiing when considering the presence of toic
secondary compounds, nutrients and digesibility.
An alternative eplanaion may be that the red
colobus populaions of Gombe and Kibale (. b.
tephrosceles) and the population at Mwanihana (.
b. gordonorum) were able to become better adapted
to eploit a diet containing a higher proporion of
mature leaves. This may be related to the types of
stomach microbes with which they have coeisted
through their evoluionary history. They may have
some physiological and/or anatomical adaptaions
for exploiting such food items. For instance, the
grey langur (Presbytis entellus) and purple-faced
langur (P. senex) in Sri Lanka tend to select ripe
and unripe fruits, respecively. This has been cor-
related with diferences in their intesinal
mucosae (Hladik, 1977; Clutton-Brock, 1977).
An addiional and perhaps complementary

explanation may be that the use of more mature
leaves by the red colobus of Kibale, Gombe and
Mwanihana is an adaptaion towards reducing
interspecific compeiion, as suggested for G. b.
gordonorum by Wasser (Chapter 13). Moreover,
the observaion of less mature leaf feeding in the
Zanzibar red colobus, serves to support Marsh's
(l 98la) hypothesis that mature leaves will be
eaten more often in forests of high tree and
primate species diversity.
Feeding on animal matter is uncommon in red
colobus and other colobines: it has been observed
in Colobus guereza (Oates, 1977), . satanas
(McKey, 1978), Presbytis entellus and P. senex
(Hladik, 1977) and P. ubicunda (Davies, 1984).
This may be because colobines obtain some
animal protein through digestion of fore-stomach
microbes (Parra, 1978).
Drinking of water is uncommon among red
colobus and other colobines (as already men-
ioned), possibly because water produced physio-
logically and during fermentation of food may
meet the monkeys' water requirements.
Charcoal eaing is unique to the Zanzibar red
colobus. One of the beneits of charcoal eaing
may be absorpion of gases. Charcoal tablets are
used in human medicine as an absorbent for the
purpose of reducing flatulence (Cook & Marin,
1951; Hall, Thompson & Strother, 1981);
however, Potter, Ellis & Levitt (1985) showed that
activated charcoal does not influence gas forma-
tion in vitro or in vivo. Charcoal may also absorb
toins from the gut: because of its absorbent
properies acivated charcoal is used in reament
of human poisoning (Cook & Marin, 1951; Pot-
ter et al., 1985). Thus, although the actual cause
of charcoal eaing behaviour is unknown, its
effects may be beneficial to the monkeys. The
behaviour may be unique to the Zanzibar red col-
obus because it forages more frequently at ground
level and also because of greater availability in
Zanzibar from charcoal kilns and bush fires.
Red colobus may also show preferences (selec-
ivity) between plant species for high nutrients
and against antifeedants (ibre and toins). For
example, Albizia gummifera has high concentra-
tions of protein relative to other species in Jozani
(Zanzibar) (Mturi, 1991). More than 85% of