Study area
This study was carried out at Lake Ol’ Bolossat (0°5’24.84”S,
36°25’4.77”E; elevation 2330masl), a 43.3 km2 inland
lacustrine wetland located in the central highlands of Kenya in
Nyandarua County (Krhoda, 1992)from December 2017 to October 2019. The
study was restricted in a block measuring 720 km2. The
lake is generally oriented in a north-south direction stretching for
c.30 km. The diversity of vegetation creates a variety of habitats and
microhabitats – from open water to perennial marshes. Open water
occupies c.23 km2from the central part towards the
south, where the lake is wider (c.4 km) and deeper. The rest of the area
(c.20km2) are marshes, dominated by sedges e.g.Cyperus sp., Papyrus sp. (only found in the extreme
northern end), and Typha sp., and this is the available habitat
for waterfowls such as Grey Crowned Crane that use the marshes for
foraging, roosting, nesting and rearing young. These marshes in some
parts are characterised by floating bogs that shift positions depending
on strength and direction of prevailing winds.
The lake basin and riparian grasslands are heavily encroached and grazed
throughout the year, with the number of livestock increasing
tremendously during the dry season (usually from December to March). The
study area falls within an equatorial type of climate receiving a
bimodal rainfall pattern as described by Brown & Britton (1980).
However, this pattern is no longer predictable due to the effects of
climate change as experienced from field observations during the study
period. The lake has a history of drying up leaving scattered pools of
water, the last such time being in 1992 (Gichuki & Gichuki, 1998). The
study area has over 120 man-made or natural wetlands. Twenty of these,
whose areas varied from 0.042 ha (420m2) to 211 ha,
were part of this study.
The lake shoreline was divided into sections (breeding sites) described
using the local village names. Clockwise, these sites include Ziwani,
Mairo-Inya, Githungucu, Kanguyo, Ngurumo, Makereka, Iria-Ini, Gakoe,
Kirima, Mugathika, Mukindu, Bahati, Karandi, Fuleni, Gatumbiro, Kanguu
and Kianjata.