Distribution of Raptors in the City Metropolitan, Nairobi, Kenya

Abstract

Diurnal raptors are a great group of birds to use for environmental monitoring. Being at the top of the food chain, raptor populations indicate the health of an ecosystem in general and show gradual trends as occasioned by environmental changes. Nairobi is a fast-developing urban metropolis and its development has led to reduction of green spaces in most places where there were forests and woodlands. This study was developed to help quantify the importance of urban forests by using diurnal raptors as indicators of forest value. Line transects were conducted in three large forest blocks within the greater Nairobi metropolitan; namely Karura Forest, Ngong Road Forest and Thogoto Forest. A metropolitan road transect was also developed to overlap the three study forests and then incorporate all the major development zones around the city. These transects were used to count all diurnal raptors seen or heard and then comparisons were computed to quantify the differences between the three forests individually. Secondly, the three forests as one single block, were compared against the city metropolitan. The study identified 15 diurnal raptor species in the three urban forests. The Shannon diversity index results showed that Thogoto Forest had the highest raptor diversity index (Shannon) at 1.08, followed by Ngong Road Forest Sanctuary at 1.05 and the lowest was Karura Forest at 1.03. However, the Analysis of Variance (ANOVA) results queried on the diversity indices showed that the indices were not statistically significant. Therefore, despite each forest having some species that did not occur in the other two forests; the three urban forests did not differ significantly in the numbers of species represented. Species encounter rates were computed per 100 kilometres to check for differences in species abundances across the three forests. A chi-square test of independence was done to examine the relation between species encounter rates across the three urban forests. The results showed that; species that were more abundant in one forest, were not as abundant in the other forests. When the three forests were compared against the metropolitan area; the urban forests had a significantly higher diversity mean score than the metropolitan area. This meant that the urban forests had more raptor species represented than the general metropolitan. Diurnal raptor abundances were also compared between the urban forests and the metropolitan area; and it turned out that those species that were more likely to be encountered in the forests were not as likely to be encountered in the greater metropolitan region. The months of March and April recorded the highest raptor numbers in the three forests with June recording the lowest numbers. In the metropolitan the months of March, April and May recorded the highest raptor numbers while December recorded the lowest numbers. This study showed that the existence of urban forests has an effect on diurnal raptor species diversity and abundance in the greater Nairobi area.