Tana Delta Irrigation Project, Kenya: An Environmental Assessment

Rehabilitation of the Tana Delta Irrigation Project, Kenya: An Environmental Assessment.
Table 15. Number of troops and estimated number of individuals of primates in the
TARDA managed areas.
Forest Forest #
# of troops of
Colobus
(est. troop size)
# of troops of
Mangabey
(est. troop size) Sykes Baboon
Sailoni 1 46 0 1 (20) 1 0
Sailoni 2 47 0 0 0 1
Kulesa East 1 48a 0 1 (15) 3 1
Kulesa East 2 48b NC NC NC NC
Kulesa West 1 49 1 (8) 0 1 0
Kulesa West 2 50 0 0 1 0
Wema West 1 53 0 0 1 1
Wema West 2 54 0 0 0 0
Wema West 3 55 1 (8) 0 1 1
Wema East 1 56 0 0 0 1
Wema East 2 57 0 0 1 0
Hewani West 1 58 7
3 (3,20,V) 2 1
(7,8,8,9,10,12,17)
Hewani East 1 59 1 (7) 0 0 1
Hewani East 2 60 2 (4,7) 0 1 0
Hewani East 3 61 0 0 0 0
Hewani West 2 62 - - - -
Hewani South 1 63 0 0 0 1
Hewani South 2 64 1 (9) 4 (10,20,35,V) 2 1
Bvumbwe North 65 0 1 (15) 1 1
Bvumbwe South 66 0 0 0 0
Lango La Simba 67 1S 0 1 0
Wema East 4 68 0 1 (6) 21S 1
Mitapani 1 69 0 1 (5) 1 0
Mitapani 2 70 NC NC NC NC
Unknown 1 (16) 0 0 1
NC – not censused
V – vocalisation
For the most part (except forest 46 and #69), mangabeys were sighted in the six largest forest
patches (#48a, 55, 58, 64, 65, 68). This makes the population highly fragmented and prone
to genetic isolation due to the distances between these forest patches. However, there may
be some movement between forests as perhaps the troop of mangabeys seen in forest #49 in
2001 is the same troop as observed in forest #46 in 2005.
Colobus on the other hand, were found in forests of varying size. There is a clear
concentration of colobus between forest #55 to the north and #64 to the south and on the
west side of Tana River and on the east side between the river and the road. Clearly the
centre of the population is in forest #58. A much smaller population lies in the northern part of
the TARDA managed area where two troops were found but as obligatory arborealists, group
isolation likely exists between the two populations and between populations on the east and
west side of the river.
Temporal Trends
Overall, for both colobus and mangabeys, their ranges have changed over time. For colobus,
the distribution has remained in a similar pattern with two populations, a very small one to the
north in the forest block of #46, 47 and 49 and one to the south centred on forest #58. There
appears to be an increasing trend of red colobus troops in forest #58 perhaps due to the
complete loss of forest #62. The range restriction generally comes from the loss of groups in
outlier and isolated forests, specifically forests #48, 53, 54, 56, 63, 67, 68.
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