Zanzibar red colobus
The Zanzibar red colobus
(Piliocolobus kirkii) is a species
of red colobus monkey endemic to Unguja, the main island of the Zanzibar Archipelago
, off the coast of Tanzania. It is also known as Kirk's
red colobus after Sir John Kirk
, the British Resident of Zanzibar who first brought it to the
attention of zoological science. It is now classified as an endangered species and in the mid-1990s was adopted as the flagship species for conservation in Zanzibar. The population is still
decreasing, and conservationists are attempting to work with the local
government to devise a proper, effective strategy to protect the population and
habitat. Challenges include the species' habitat, which is limited to the
archipelago. The species has been reclassified three times; it was previously
in the genus Colobus, then in the genus Procolobus, and later in the genus Piliocolobus.
Evolutionary history and taxonomy
The Zanzibar red colobus, Piliocolobus
kirkii, population on Zanzibar, represents a population of red colobus that
is believed to have been isolated on the island after sea levels rose toward
the end of the Pleistocene epoch. Furthermore, it is suggested through
mitochondrial analysis, that phylogenetic groups within the red colobus have
been genetically isolated from another since the Pliocene.
Examining cranial morphology has shown that P.
kirkii has diverged from mainland Piliocolobus to its own species. It has
experienced an acceleration in morphological evolution of size which is
suggested to be the result of insularity on the island and environmental
pressures such as competition, habitat, predation and/or resource availability.
There has been no evidence for population bottlenecks in
the species.
The smaller cranium of P. kirkii
in
contrast to the mainland colobus monkey, is consistent with Foster's rule (also known as the island rule)
in which the original (larger) animal becomes smaller over time when there are
limited resources. Males tend to have pedomorphic traits which include a shorter
face, large orbits and an enlarged neurocranium. It is not certain how long ago and
where this evolutionary change occurred.
Through molecular analyses, it is indicated
that P. kirkii is more closely related to the Udzungwa red colobus (P.
gordonorum) compared to other red colobus species. This analysis has
also placed the divergence of P. kirkii from its sister species P.
godronorum at about 600,000 years ago, which actually allows for
an older evolutionary age compared to the previous assumption that it had
become its own species around the last glacial period.
The species has been reclassified twice; it was previously in the genus Colobus, and more recently in the genus Procolobus and then the genus Piliocolobus.
An alternative common name is Kirk's red colobus
after Sir John Kirk (1832–1922),
the British Resident of
Zanzibar who first brought it to the attention of zoological science.
Physical description
This Old World monkey's coat ranges from dark red to black,
accented with a black stripe along the shoulders and arms, and a pale
underside. Its black face is crowned with long, white hair, and features a
distinguishing pink mark on its lips and nose. Also, the Zanzibar red colobus
has a long tail used only for balancing — it is not prehensile. Sexual
dimorphism is generally decreased in the species, meaning the females have
little difference in their body size and colour from their male counterparts. Females usually outnumber the males in their
groups. The species has a notably small cranium and rotund body shape, with
males potentially reaching over 12 kg and females, 10 kg. In adults, highly differentiated facial features help them to
distinguish each other in a group.
The word "colobus" comes from Greek ekolobóse, meaning "he cut
short", and is so named because of the significant reduction in size, or
complete lack of an opposable thumb in comparison to other primates. To make up for this, they have four long digits that align to form a
strong hook, allowing them to easily grasp branches and climb.
Locals on the island have called the Zanzibar redcolobus kima punju which means "poison monkey"
in Swahili because
of their strong smell unlike other monkeys. This has caused people to hold
negative views of the monkey and even to say it has an evil influence on trees
on which they feed, ultimately killing the trees.
Habitat
The Zanzibar red colobus is found in three forests
of the Zanzibar archipelago. It displays a
wide habit tolerance, but it is mainly an arboreal species and prefers drier areas over
wet ones. Its habitats include coastal thickets and coastal rag scrub, but it
can also be found in agricultural areas
and in mangrove swamps; the latter provides food
year-round. When found in agricultural areas, the monkey is
more used to humans and comes closer to the ground.
About 1,600 to 3,000 individuals remain, and currently, 50% of the monkeys found on the islands live outside
protected zones. The largest and most significant area of protection
and habitat for the monkey is in Jozani
National Park, which provides 25 km2 (9.7 sq mi) of land reserve. It is located on the main island and the populations here have
been greatly studied in regards to both their ecology and behavior. Even so,
many groups have been found in shambas (Swahili for
"farmland") in close proximity to the park. In these shambas adjacent to the park, higher
densities of the red colobus have been reported living here in more cohesive
groups, compared to inside the park reserve. The incidence of
some of these monkeys living permanently outside the zone of the protected park
reserve can increase the endangerment of the groups.
Behavior
The groups
consist of up to four adult males and many adult females; typically yielding a
1:2 ratio of males to females. Young of varying ages are
also incorporated in the group. The number of monkeys in a group can range from
30 to 50 individuals. The species is a very social animal, and can often be
observed playing and grooming during the rest periods between meals. Unlike
females, in a group, males actually maintain close bonds, acting together in
defense of their group and even in grooming each other.
Feeding
Feeding is also a group activity. It begins to feed
in the morning, and is more active during the cooler parts of the day. Loud
calls from males indicate the group is ready to move to another tree to feed.
This monkey is mainly a foliovore,
and on average, half of the leaves consumed are young leaves. They also eat
leaf shoots, seeds, flowers, and unripe fruit.
It has also been found eating bark, dead wood,
and soil. It is one
of the few species that do not eat ripe fruits; it has a sacculated stomach with four chambers specific for
breaking down plant materials, however it cannot digest the sugars contained in
mature fruits. Because the monkey feeds on young leaves (though
not limited to them), there are instances where it consumes charcoal, which is believed to aid their digestion
of the toxins (possibly phenolic compounds) found in the young leaves
of the Indian almond tree and mango tree. The habit of consuming charcoal is thought to be a learned
behavior presumably passed on from the mother to her offspring. It has been noted, however, that not all populations on the islands
carry out the behavior, but that it is rather mostly done by those who consume
more perennial and exotic foliage.
Since some populations use mangroves as a source of
food, it is natural for the monkey to consume more sodium chloride (NaCl). Because of this,
those populations have been observed to drink water directly from tree-holes,
or licking water off of leaves. This innovative behavior shows the adaptation
of the monkey to novel ecological and environmental circumstances.
In the dry season, one of the staple foods, Indian almond tree,
as previously mentioned, drops its leaves and can cause the monkey to go beyond
park boundaries in order to extend its feeding range. This puts the already
endangered colobine at
more risk.
Reproduction
Males usually reach sexual maturity at about 3–3.5
years old, while females reach it at about two years old. Females approaching estrous can be easily identified because of
the swelling and bright red
coloration of the genital area. This signals to males that the
given female is ready for mating. Moreover, just
prior to mating, males will use their fingers to probe the female's birth
canal. This is immediately followed by sniffing the area because estrogen and progesterone can be detected by this method,
further helping the male conclude if the female is indeed ready to breed.
Gestation is about 6 months for colobus monkeys and
one female has about 1–2 new-born every two years. Parental care is intense and
often, the role is shared by multiple females of the group. It is observed that
about 76% of offspring are born between September and December. Infanticide has also been noted on occasion
when a new male joins a given group that has infants.
Research has suggested that the ability for dietary
expansion, which consuming charcoal partly allows, explains the higher birth rates
and densities due to resource availability. Birth
rates for those living in mangroves are higher than colobus monkeys living in
coral rag forests.
There are higher birthing rates between
October–December for colobines on Uzi Island and then January–February for
those in Kiwengwa, located on the eastern side of the main
island. Infant mortality can be significantly high with
half of the infants born not reaching more than six months of age. The birth rates themselves, however, are actually decreased in
comparison to mainland colobus monkeys and interbirth intervals are longer as
well. Research has suggested that this is a
consequence of disturbed habitats in which mainland colobi are not so affected.
Communication
The red colobus species have a smaller larynx compared to other members of the Colobinae subfamily. The male's call is more of an alto or
soprano in contrast to the low bass of a male's in black-and-white colobus species.
The Zanzibar red colobus is non-territorial in nature and as so does not
typically make loud, territorial threat calls. Zanzibar red colobus distress
and warning calls are the "bark", "chist", or
"wheet". One of the loudest calls from the monkey is heard when he
expresses his dominance over the group and when checking the sexual status of
his females.
The call heard most often by people in or
near Jozani
Forest is the 'alerting signal'. This is an attention-getting
call that is derived from the progression call. Chirps and grunts are made when
there are changes in the surrounding environment such as changes in weather or
animal movement in proximity to the group. With most arboreal animals, there
are two different alerting calls, one for when a predator is on land, and
another when there is an aerial predator. However, because of the lack of
larger birds of prey in
Zanzibar, such calls are not often witnessed. The young, on the other hand,
because of their smaller size and vulnerability, do at times make such calls
when they see shadows.