Nest Niche Separation and Coexistence of Understory Mixed-Species Flocks Birds in Subtropical Forest

Mixed-species flocks of birds are common in tropical and subtropical forest worldwide. In South China, babblers (Timaliidae) are the main members of these flocks. Most of babblers are small-bodied insectivores. Niche separation and coexistence of these species within the mixed-species flocks are hot ecological issues. A study of the nesting niche of understory birds at Guangdong Dinghushan National Nature Reserve (DNR) and Guangdong Yunan Tongledashan Provincial Nature Reserve (TNR) was carried out by systematically searching for bird nests during the breeding seasons of 2016 and 2017. Niche width and niche overlap of nesting habitat types, nesting substrate and nesting height were compared for 7 species. The grey-cheeked fulvetta (Alcippe morrisonia) was found to have the largest niche breadth in all three variables. This may explain why grey-cheeked fulvetta is the dominant species in mixed-species flocks in South China. The niche overlap values were 0.85±0.01(n=10) in DNR, 0.76±0.02 (n=10) in TNR for nesting habitat types, 0.20±0.08 (n=10) in DNR, 0.23±0.12 (n=10) in TNR for nesting substrates, and 0.26±0.09 (n=10) in DNR, 0.35±0.20 (n=10) in TNR for nesting heights. There was high niche overlap for nesting habitat types, but lower niche overlap for nesting substrates and nesting heights. This implies that niche separation of nesting substrate and nesting height may decrease competition for resources between species in the same flocks. This study of breeding niche overlap helps to explain how species in mixed-species flocks can coexist.