Bird Community Composition and Functional Guilds Response to Vegetation Structure in Southwest Ethiopia

Abstract

Shade coffee farms in southwest Ethiopia are known to host high levels of avian biodiversity. However, these farms vary in terms of forest management, which affects their understory, mid-story, crown cover, and canopy closure, and hence their structural complexity. Such differences in vegetation structure can potentially affect the survival of specialist bird species, and shade coffee farms may not equally contribute to avian biodiversity conservation. This study aimed to investigate how avian community composition, richness, and the relative abundance of different bird functional guilds relate to structural differences in vegetation shaped by forest management. Bird guild classification was based on bird species forest dependence, diet type, migration status, nest type, foraging, and nesting strata, and bird communities were surveyed using the Timed Species Counts (TSCs) method. Species turnover in bird communities was evaluated using detrended correspondence analysis and redundancy analysis, whereby multiple regression models were used to examine bird guild responses to vegetation structure. Total bird species richness and relative abundance did not respond to vegetation structure. However, the richness of forest specialists and understory foragers, and the relative abundance of mid-high foragers, all positively related to tree diameter at breast height (DBH) and crown cover, whereas the relative abundance of species with medium levels of forest dependency, mid-high/canopy foragers, and open-nesters were positively related to basal area and canopy cover. This study demonstrates that the relative value of shade coffee farms for avian biodiversity conservation depends on the type of forest management, and that bigger trees with larger crown cover provide a habitat of higher quality to habitat specialist birds.