Walia Special Edition on the Bale Mountains (2011) - Zoologische ...

interactions? 2) Would such classification of species in to communities be reliably detectable in the
field? Further questions are as follows: Can one consider the whole bird assemblage of the BMNP
as members of a single community or several communities? If the latter, what is the species pool
of each community? Is there intercommunity difference in composition across habitat types? Can
such classification reflect the distribution of resident birds across different habitat types within each
ecosystem?
Methods
Study area
The Bale Mountains National Park located at 6030’- 7o00’ N, 39030’- 39055 E is part of the South-
Eastern highland massif in Ethiopia and contains the largest extent of Afro-alpine habitat in the
continent (Sillero-Zubiri 1995). It encompasses an area of 2200 km2 with elevation varying between
1400 m to 4400 m a.s.l. (Hillman 1986). Topography within the BMNP can be divided in to three
categories by elevation-the northern slopes between 3000 and 3800 m a.s.l.; the central plateau
and peaks between 3800 and 4400 m a.s.l.; and the southern escarpment from 1400-3800 m a.s.l.
(Hillman 1988). Depending on slope, aspect and soil types, each of these areas in the park has its
own characteristic vegetation. In the northern slopes a mix of Juniperus/Hagenia/Hypericum where
montane grassland and heath dominates near the tree line; sparse afro-alpine vegetation at its center
and; and the vegetation in the southern escarpment constitutes Erica/Hypericum/Hagenia/Aningeria
and Podocarpus. A bimodal local climate with two wet seasons that have heavy and small rains
is characteristic to the site. The heavy rains occur from July to October, with the highest peak in
August and the small rains from March to June, with a peak in April. Records show that this area
experiences temperature extremities particularly in areas of the highest altitudes during the dry
season and more or less the same pattern of warm during the wet season. The highest temperature is
18.4 Co in February and the lowest is 1.4 o in January (Hillman 1986).
Structuring of the avi-fauna of the BMNP
Censuses conducted between November 2002 and October 2005 determined a total list of resident
birds composed of 117 species in the National Park (NP). The range of species includes wetland
birds to small passerines that inhabit forest and afro-alpine moorland habitats. As much as the
habitat preference of groups of species, their diet and related ecological and morphological features
are diverse (Fry et al. 1992; Zimmerman et al. 1996; Sincliar and Ryan 2003). This suggests the
total bird assemblage of the NP may contain a group of species that may be assembled to form more
than one community. The possibility of such phenomena was explored by gleaning data from the
literature that helped to evaluate the potential of interspecifc interactions.
Interaction amongst species is defined as the ability of each to affect the resource level
that is available to one or more of species that co-occur with it both in space and time (Daimond
1975; Rice and Kronlund 1997). Resources for a species include food, breeding habitat and cover
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 17