Water depth, vegetation height and water edge distance are critical in
nest-site selection for Grey Crowned Crane at Lake Ol' Bolossat, Kenya
Abstract
Grey Crowned Crane Balearica regulorum is described as an icon of
Africa’s wetlands and grasslands and is listed as Endangered on the IUCN
Red List of Threatened species. Efforts towards its conservation actions
are nonetheless hindered by among others, lack of knowledge on factors
influencing breeding productivity such as nest-site selection. Factors
influencing the probability of nest-site selection were investigated at
Lake Ol’ Bolossat, a 43.3 km2 wetland located in the central Kenya
highlands as a breeding resident. The number and distribution pattern of
breeding pairs was also determined. A total of 123 breeding pairs were
recorded, 103 in the lake and 20 in the surveyed satellite wetlands thus
providing the largest database of breeding Grey Crowned Cranes reported
in Kenya to date. Mean breeding pair density for the lake’s marshes was
6.50±0.84 (SE) pairs/km2 with a mean distance between nests of
302.53±17.02 (SE) m. Generalized Linear Models were used to select the
most important environmental variables explaining nest-sites selection.
The model selection algorithm yielded a subset of 8 best models, where
the most important predictor variables (i.e. those with ΔAICc
<2) were determined as water depth (preferred above 50 cm),
vegetation height (above 60-90 cm) and distance from the water edge
(ca.100 m). Water depth and vegetation height had positive effects on
nesting probability while the distance to water edge exhibits quadratic
tendency. These findings provide key insight into Grey Crowned Crane
nesting ecology and a basis for breeding habitat modification and
management. This study underscores the importance of Lake Ol’ Bolossat
as a critical breeding site and its significant role in the species’
population recovery and survival. The lake should consequently be
re-gazetted as a National Park to ensure effective and sustainable
control of anthropogenic activities in and around the lake in favour of
Grey Crowned Crane.