User:Raf Aerts/Notebook/Open Coffee/2008/09/03

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Field notes on the birds of Geruke

The forest fragments in Geruke (Fig. 2) seem to have a less diverse (or less conspicuous) avifauna than the forest fragments in northern Ethiopia (see Aerts et al. 2008). During trial one-hour species counts (count protocol: Freeman et al. 2003), we observed only 10–15 bird species per count (in northern Ethiopia, the maximum number of species observed in a single non-aquatic site during one hour was 46). Also, most species were observed rather soon in each count. These trial counts suggest that Geruke has a species-poor bird community with few, but abundant, species. Similar observations were recorded in nearby Bonga, where only 72 bird species were observed in 19 coffee forest patches (Gove et al. publication in Conservation Letters pending). This is not what one would expect, as some species which are considered robust indicators for a healthy forest microclimate such as Black-headed forest oriole and Black-and-white colobus are very common. This leads us to hypothesize the following:

  • The richness of the northern forest fragments is an effect of extreme fragmentation, concentrating many bird species that rely on forest resources in the scarce forest fragments;
  • Disturbance and edge effects cause high habitat heterogeneity in the northern fragments, attracting a wide variety of matrix species into the forest fragments;
  • Simplification of the vertical structure in the coffee forests has led to a decline of forest bird species richness.

The most common species in the area include Common bulbul, Thick-billed raven, Cape rook, Hadada ibis, Lapped-faced vulture, Variable sunbird, Tacazze sunbird, Barn (?) swallow and Grey-headed sparrow. In Jimma locally common species include Greater blue-eared glossy starling, Black-headed weaver, Grey-headed kingfisher, Sacred ibis, Wattled ibis and Hamerkop. In the forest fragments, Klaas cuckoo, Black-headed forest oriole, Common camaroptera, Common bulbul and Tropical boubou are among the most common species. Rare species included Paradise flycatcher (white form at Geruke; rufous form in Jimma), Black-crowned crane, Steppe eagle, Olive thrush, Rueppell’s robin chat and ambiguous forms of Hemprich’s (?) hornbill and Double-toothed (?) barbet.

Geruke-pano1024.jpg Fig. 2 Geruke - coffee forest fragments in an agricultural matrix