Study area
This study was carried out at Lake Ol’ Bolossat (0°5’24.84”S,
36°25’4.77”E; elevation 2330 m above sea level, Figure 2) from December
2017 to October 2019. This lake is a 43 km2 inland
lacustrine wetland located in the central highlands of Kenya in
Nyandarua County. It has characteristic features of Rift Valley lakes
such as being shallow and narrow (stretches for c.30 km oriented in a
north-south direction). The diversity of vegetation creates a mixture of
habitats and microhabitats – ranging from open water to perennial
marshes. The open water occupies c.23 km2 from the
central part towards the south, where the lake is wider (c.4 km) and
deeper (1.5-2.5 m). The rest of the area (c.20 km2) is
comprised of marshes, dominated by sedges, for example Cyperussp., Papyrus sp. (only found in the extreme northern end), andTypha sp., and this is the available habitat for waterfowl such
as Grey Crowned Crane that use them for foraging, roosting, nesting and
rearing chicks.
The lake basin and riparian grasslands are heavily intruded by humans
for quarrying, settlements, crop farming and livestock grazing. Grazing
happens throughout the year, with the number of livestock increasing
during the dry season (from December to March) in most years. 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. For
example, the 2017/2018 breeding season, whose commencement is marked by
nest construction and egg-laying, lasted between July and February (8
months), compared to 13 months (April 2019 – April 2020). Romίrez et.
al. (2018), reporting climate change as an emerging issue in waterfowl
communities (and wetlands) conservation, predicts that it will affect
them in different ways depending on their life-history strategies, with
resident species (like Grey Crowned Crane) being affected more than
seasonal visitors. There are over 120 man-made or natural wetlands
around the lake ranging in size from 420m2 to 211 ha
that are also used by cranes for feeding, roosting and nesting, but none
was included in this study due to a few accessible nests and their
ecological features variability compared to the lake.
The shoreline was divided into 17 sections to identify critical cranes
breeding sites described using village names: Ziwani, Mairo-Inya,
Githungucu, Kanguyo, Ngurumo, Makereka, Iria-Ini, Gakoe, Kirima,
Mugathika, Mukindu, Bahati, Karandi, Fuleni, Gatumbiro, Kanguu and
Kianjata. These sites were grouped into three by dividing the lake into
3 parts (north, middle and south; Figure 2) each of c.10 km long. These
sections helped to identify critical areas for cranes.