Population, flocking behaviour and habitat selection of the Grey Crowned Crane Balearica regulorum at Lake Ol’ Bolossat basin, Kenya

Abstract

Lake Ol’ Bolossat is an inland wetland located in Nyandarua County, Kenya that provides critical year-round habitat for the Globally Endangered Grey Crowned Crane Balearica regulorum gibbericeps. This study aimed at establishing the population size and density of cranes in the basin, ratio of young to adults (as a measure of productivity), and habitat selection and use during the breeding and non-breeding seasons. Using complete ground counts, five censuses were conducted between 2017 and 2020 with between 521 and 1115 cranes recorded, and we estimate the local population size to be 250–350 individuals. Population density ranged from 0.99–2.18 cranes/km² during the breeding and non-breeding seasons respectively. From all 219 observations made during the study period, the  mean flock size was 28.21 with a maximum flock size of 332 and a modal flock size of 2–25 individuals. The average proportion of young cranes across all counts was 11.65% indicating a population which is breeding successfully. Although cranes occupied both wetlands and terrestrial habitats in almost equal proportions across the year cumulatively, the difference in choice of habitat between the breeding and the non-breeding seasons was significant (χ²=489, df=1, p=0.0001), whereby more cranes (mostly paired individuals) were observed in marshes during breeding months. Wheat fields were the most often used of terrestrial habitats among fields of different crop types sampled. Holding 14% and 5% of Kenya’s and the global population of Grey Crowned Cranes, respectively, Lake Ol’
Bolossat is undoubtedly an important site for this species’ conservation and survival.

Keywords: Lake Ol’ Bolossat, Balearica regulorum gibbericeps, habitat selection, population size, flock characteristics