Tana Delta Irrigation Project, Kenya: An Environmental Assessment

Rehabilitation of the Tana Delta Irrigation Project, Kenya: An Environmental Assessment.
Even for colobus, an obligatory arboreal species, riverine forest, isolated trees and small
forest patches may provide adequate tree cover to allow for dispersal between larger forest
patches explaining the changes of pattern of troop locations through time, with due
consideration to census error. Possible seasonal changes of movement must also be taken
into account.
On the other hand, mangabeys previously appeared throughout the census area in all but
seven (31.8%) of the forests. As recorded in this census, their range has expanded into
forests that previously did not report mangabeys (forest #46 and #69). Nine forests (40.9%)
with previous records of mangabey did not have mangabeys noted in 2005. Interestingly,
three troops are missing from the forests on the west side of the river (#54, 59, 62) in the
vicinity of forest #58 while forest #58 has three troops more than previously reported in the
2001 census. Inter-forest movement of groups may account for this.
Comparing the forest area of the current census to the map of forest areas generated by
Karere et al. (2004), this survey did not census the northern portion of forest #56 or 63b, 67b.
Interestingly, two troops of colobus accounted for in the 2001 study (one each in forest #63
and #67) that were not counted in this census, come from these forests. It is possible, that
these uncounted troops were previously observed in these uncensused forest patches.
Complete loss of both species of primate has occurred in five of the 22 areas censused
(22.7%) however only Wema West 2 (#54), had both species missing. This forest was noted
in 1994 for having “moderate human activity”.
The other forests which had complete loss of groups, either colobus or mangabey had varying
levels of human activity as noted in Table 3. Please note that the activity level noted in Table
5 may well have changed from 1994 description as it has been stated that forest clearing has
escalated since then (Wieczkowski et al., 2002). There may not be a direct relationship
between forest disturbance and primate group density but that disturbance may lead to
reduced group sizes rather than a reduction in troops (Muoria et al., 2003).
Table 16. Levels of disturbance in forests that have lost colobus and mangabeys in
this census.
Colobus
Mangabey
Forest # Human Reference Forest # Human Reference
Activity
Activity
47 Light Butynski and Mwangi 1994 49 light Butynski and Mwangi
1994
48 Heavy Butynski and Mwangi 1994 54 moderate Butynski and Mwangi
1994
54 Moderate Butynski and Mwangi 1994 56 cleared Muoria et al., 2003
areas
63 Moderate Muoria et al., 2003 57 heavy Muoria et al., 2003
68 cleared
areas
Muoria et al., 2003 59 cleared
areas
Muoria et al., 2003
93