International Journal of Molecular Evolution and Biodiversity 2016, Vol. 6, No. 1, 1-12
6
both during dry (SI=0.31) and wet (SI=0.44) seasons. This is probably due to the similarity of vegetation structure
between the two habitat types. Study carried out by Erdelen (1984) also showed significant correlation between
diversity of bird species and the vegetation structure. As the vegetation layer increases, the number of available
niches for birds also increases and so does the diversity of avian species. This is due to the different feeding habit
of birds leading to niche separation (MacArthur, 1964).
In the present study, the highest number of bird species was recorded in the woodland (87 species) followed by
riverine forest (53 species). This might be due to higher vegetation complexity of the woodland and riverine forest
than wetland. This finding is in line with MacArthur (1972) and Smith (1974), who reported that habitats with
complex vegetation can provide stable source of food, nesting and cover from predator for different avian species.
Tellaria and Santos (1994), also pointed out that habitat structure affects distribution of individual species of birds.
Besides, foraging modes (Marone, 1991) and floristic composition (Wiens and Rotenberry, 1981) have influence
on the distribution of birds. Besides, habitat size (Willis, 1979) has influence on the distribution of avian. The
small size of the riverine forest in the study area might have contributed to the less number of species compared to
the woodland.
The seasonal variation in the availability of food resources result in seasonal changes in the species abundance of
birds (Karr and Roth 1971; Gaston et al., 2000). The uncommon species may be related to the breeding nature,
large home range and niche of the species. In addition, degradation of the habitat might be a reason for the species
to be uncommon (Ryan and Owino, 2006). The abundance of many bird species are determined by the
composition of the vegetation that forms a major element of their habitats. As vegetation changes along complex
geographical and environmental gradients, a particular bird species may appear, increase or decrease in number,
and disappear as the habitat changes (Lee and Rotenberry, 2005).
The number of bird species (124) recorded in this study does not represent all the avian species present in the
study area, but can update some of the avian species present in the study area. If an exhaustive survey is made in
all the habitats (including grassland) by increasing the length of the study period and the sampling area, the
number of species identified will be more. This underlines the area could be one of the areas with high avian
diversity in Ethiopia.
Acknowledgements
We thank Jimma University for the financial support. Oromia Regional State Park Development Office and Dhati Walel National
Park warden and all scout members need to be acknowledged for creating a homely working environment and their unlimited
friendly relationship during the field investigations in the Park.
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