Factors Affecting Population, Nesting Habits, and Conservation of Grey Crowned Crane (Balearica Reguloram, Bennett 1834) in Lake Ol’ Bolossat Basin, Kenya

Abstract

Birds are significant drivers of ecosystem processes and are therefore sensitive to natural and human-induced changes. Cranes are a highly threatened bird family and Grey Crowned Crane (Balearica regulorum) is listed as Endangered primarily because of human-related activities, such as habitat modifications. This study investigated the population characteristics, nesting habits, seasonal variation in abundance and biomass of potential food, effects of Land Use and Land Cover changes, and threats affecting this species in Lake Ol’ Bolossat basin, Nyandarua County, Kenya. Five comprehensive population surveys were conducted during the study period (2017- 2020) showing that the basin supported a highly variable population, ranging from 521 and 1,115 birds corresponding to 15% and 5% of the species’ national and global population respectively. The resident population present year-round was estimated at 250-350 cranes. The population comprised of 11.65% young birds which is a good sign of a healthy population. Group sizes ranged from 1-332 cranes with a mean of 28.2±3.24. Marshes and wheat fields were the most utilised habitats throughout the year. Factors influencing nest-site selection were investigated from a sample of 30 nests. Four out of the 12 measured factors were considered in Generalized Mixed Linear Model to determine if they had an influence in nest-site selection. Except for grazing intensity, all other three factors had a significant influence (p <0.05): water depth (50cm), offshore distance (100m), and vegetation height (60-90cm). A minimum of 103 territorial pairs were recorded in the lake compared to 20 pairs in upland wetlands. Thirty-one clutches (mean 2.23 eggs; range 1-4 eggs) were described. Except for water surface temperature that didn’t show a significant seasonal variation (t = 1.89, p >0.05), all the other parameters were significant. This variation in water parameters significantly affected abundance of macro-invertebrates (F = 4.161; df = 5, 94; p <0.05). Crane’s breeding coincided with the wet season when food was abundant. Major Land Use and Land Cover changes were observed between 2010 and 2020 including an increase of 83% of open water causing a significant decrease of 73% marshes. During the same decade, native grasslands cover had a >50% decrease probably due to cultivation which increased

by 64%. Loss of marshes and grasslands has potential negative impacts on the crane’s population due to loss of foraging and breeding habitats. A total of 102 respondents were purposively selected to rank 16 predetermined threats. The most severe threats were those affecting cranes breeding activities by reducing the quality of nest-sites, reduced chicks’ survival, and an increased loss of eggs and chicks. These threats must be addressed to boost reproduction in addition to: zonation of breeding sites, implementation of gazettement notice and the management plan, allocation of funds in support of conservation and community development, law enforcement, control and management of invasive alien species, annual population monitoring, and consideration of listing the lake as a wetland of international importance and annexing it to the Aberdares UNESCO World Heritage Site.