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.