Community characteristics of forest understory birds along an elevational gradient in the Horn of Africa: A multi-year baseline

• Published in: Ornithological Applications 2021-05, Vol.123 (2), p.1-20
• Main Authors: Kittelberger, Kyle D., Neate-Clegg, Montague H.C., Buechley, Evan R., Şekercioğlu, Çağan Hakkı
• Format: Article
• Language: English
• Subjects: abondance; Abundance; Altitude; Asymptotes; avian ecology; Banding; Biodiversity; Biodiversity hot spots; Birds; Climate change; Community composition; Composition; composition des communautés; Coniferous forests; demographic rates; Demographics; Environmental degradation; Ethiopia; Growth rate; Guilds; Habitats; Massifs; montagnes tropicales; Montane environments; Mountain forests; Mountains; Ornithology; Population growth; RESEARCH ARTICLE; richesse spécifique; Species composition; Species richness; Survival; taux démographiques; tropical mountains; Understory; écologie aviaire; Éthiopie
• ISSN: 0010-5422; 2732-4621
• DOI: 10.1093/ornithapp/duab009

Tropical mountains are global hotspots for birdlife. However, there is a dearth of baseline avifaunal data along elevational gradients, particularly in Africa, limiting our ability to observe and assess changes over time in tropical montane avian communities. In this study, we undertook a multi-year assessment of understory birds along a 1,750 m elevational gradient (1,430–3,186 m) in an Afrotropical moist evergreen montane forest within Ethiopia's Bale Mountains. Analyzing 6 years of systematic bird-banding data from 5 sites, we describe the patterns of species richness, abundance, community composition, and demographic rates over space and time. We found bimodal patterns in observed and estimated species richness across the elevational gradient (peaking at 1,430 and 2,388 m), although no sites reached asymptotic species richness throughout the study. Species turnover was high across the gradient, though forested sites at mid-elevations resembled each other in species composition. We found significant variation across sites in bird abundance in some of the dietary and habitat guilds. However, we did not find any significant trends in species richness or guild abundances over time. For the majority of analyzed species, capture rates did not change over time and there were no changes in species' mean elevations. Population growth rates, recruitment rates, and apparent survival rates averaged 1.02, 0.52, and 0.51 respectively, and there were no elevational patterns in demographic rates. This study establishes a multi-year baseline for Afrotropical birds along an elevational gradient in an under-studied international biodiversity hotspot. These data will be critical in assessing the long-term responses of tropical montane birdlife to climate change and habitat degradation. LAY SUMMARY There is a dearth of baseline avifaunal data along elevational gradients, especially in Africa, impeding efforts to evaluate temporal changes in tropical montane bird communities. We assessed species richness, community composition, abundance, elevational occurrence, and demographic rates of montane understory avifauna along an elevational gradient in Ethiopia's Bale Mountains. We found a bimodal pattern is observed and estimated species richness, with high species turnover across the gradient. There were few significant changes in guild or species capture rates over time, yet we documented eight species at elevations higher than documented in the established literature. This si