Effects of fragmentation on avifaunal composition, diversity and fluctuating asymmetry in the eastern Mau forest: a case study of river Njoro watershed, Kenya

Abstract

Fragmentation and its effects on avifauna is a study that was conducted in upper River Njoro watershed covering about 280km2. The watershed is under threat from increasing human activities that have led to rapid changes in land cover and deterioration of environmental and habitat conditions for birds. These include replacement of indigenous trees with exotic types, clearing of riparian vegetation, cultivation of river banks, deforestation and forest fragmentation. The study’s main objective was examination of effects of forest fragmentation and environmental degradation on composition, diversity and fluctuating asymmetry of avifauna in natural and plantation forest fragments in the River Njoro watershed. Mist netting was used as the method of data collection. Length of sampling time per station depended on rate of capture. Captured birds were ringed and studied with detailed data recorded in Ringing Book. Statistical and descriptive analyses were performed using windows based MINITAB (Version 13.1) software. Diversity Indices were calculated for different forest fragments and data subjected to Analysis of Variance and F-test. A total of 238 individual birds from 49 species, 17 Families and 4 Orders were captured. Results show that larger continuous forest fragments have more birds and higher diversity than smaller ones, forest generalist birds are more than forest specialist birds, natural forest fragments have a higher diversity of birds than plantation forests (P<0.05), fluctuating asymmetry was, however, not observed in the birds. Based on these key findings, several conclusions are made. These include a difference in composition of birds between the forest fragments, a significant difference in diversity of birds between natural forest fragments and plantation forest fragments and environmental degradation has not caused significant genetic stress in the avifauna of River Njoro watershed since fluctuating asymmetry was not observed. The study recommends; that forest policies on plantation establishment be reviewed by Kenya Forest Service and all stakeholders to discourage establishment of monoculture plantations in the midst of natural forests, that a similar study is carried out during the dry season to capture weather variations, that regular monitoring of environmental conditions and birds be carried out to monitor trends, and lastly, long term research on genetics of birds be carried out in the watershed to serve as early warning signals and thus provide guidance on informed management decisions.