Status and habitat choice of turner's eremomela, eremomela turneri (van someren 1920) in south Nandi forest reserve -Kenya

Abstract

This study was carried out on Turner‟s Eremomela, Eremomela turneri, a globally Vulnerable bird species of mid-altitude forests. The nominate race turneri, is known only from South Nandi and Kakamega forests in western Kenya. Prior to the present study, there was very little documented about the ecology of this species particularly its recent status. The main objective of the study was to estimate the population of Turner‟s Eremomela in South Nandi Forest as well as to determine the factors best explaining its presence, distribution and habitat choice. The forest was stratified by altitude into three blocks where detailed eremomela counts and vegetation sampling were carried out. Vegetation parameters predicted to be important for its survival and hence occurrence in the forest were measured. The population of Turner‟s Eremomela was estimated to be 13,900 with an overall density of 1.06 eremomelas ha -1 . The eremomela foraged in groups of two to eight birds and predominantly in groups of four which accounted for 55.2% of all the sightings. There were no significant differences between the blocks in the group sizes. The estimated density of groups was 0.27 ha -1 . E. turneri utilised seven of the more than sixty tree species occurring in the forest. 74.1% of all the sightings were in Croton megalocarpus, while only 8.5% of trees recorded in vegetation sampling plots were C. megalocarpus. This indicate that the bird had a very strong preference for this tree species. The spatial distribution of the bird within the forest was mainly influenced by maximum canopy height and percentage canopy cover. The means of these parameters were higher in the eremomela-occupied than in the eremomela-unoccupied areas. The eremomela exhibited a high degree of micro-habitat selection. This was strongly influenced by percentage canopy cover, tree density, maximum canopy height and average canopy height. Index of tree dispersion and the number of tree with height < 10 m were negative predictors. A logistic regression model selected maximum canopy height, percentage canopy cover and index of tree dispersion (distance) as the best positive predictors of the presence of E. turneri at macro-habitat level. Maximum canopy height was the strongest predictor while index of tree dispersion (based on dbh) and minimum canopy height were negative predictors. The same model selected percentage canopy cover, the number of trees with diameter at breast height (dbh) of 10-35cm and maximum canopy height as the best positive predictors of the presence of the bird at micro-habitat level. Percentage canopy cover was the strongest predictor while index of tree dispersion (dbh) and the number of trees with height <10 m were negative predictors. The number of trees encountered with dbh > 10 cm, number of trees with height of 11-20 m and number of Croton megalocarpus and Celtis africana were selected by a normal multiple regression model as the factors important in influencing the density of the bird in the forest. The factors important for the survival of E. turneri in S. Nandi Forest, particularly canopy cover, canopy height, tree height and the abundance of C .megalocarpus have been changed by logging among other forest uses. This has resulted in loss and fragmentation of the bird‟s optimal habitats. Presently, these optimal habitats occur as patches or „islands‟ within a matrix of degraded forest. This in turn has affected the spatial distribution of the bird in the forest with a bias towards the low altitude areas (block L) which is less disturbed. Though South Nandi Forest appears to be the world‟s stronghold of this race turneri, forest encroachment and the present logging (concentrating on C. megelocarpus) are a serious threat to the bird‟s continued survival. A comprehensive conservation and management plan for the forest is urgently needed.