Dietary niches of birds in Hong Kong

Abstract

Understanding the dietary niche of birds has significant implications for the trophic interactions in ecosystems. Hong Kong has remarkably high biodiversity in both habitats and avian species. However, the dietary niches of many birds in Hong Kong remain understudied. The distinctiveness of dietary niches enables species coexistence and promotes biodiversity. This thesis investigated the dietary niche of birds in Hong Kong, with a focus on niche partitioning and their functional role as plant seed dispersers.

This thesis first analyzed the stopover diets of the critically endangered Yellow-breasted bunting (Emberiza aureola) and five other sympatric bunting species, namely Little bunting (Emberiza pusilla), Chestnut-eared bunting (Emberiza fucata), Yellow-browed bunting (Emberiza chrysophrys), Black-faced bunting (Emberiza spodocephala) and Rustic bunting (Emberiza rustica) in Hong Kong. A total of 109 faecal samples were analyzed using DNA metabarcoding with multiple markers (18S, ITS2 and COI) to ensure a comprehensive coverage of dietary diversity. It was revealed that all bunting species primarily consumed Poaceae, with the Yellow-breasted bunting occupying a distinct niche by consuming a high proportion of cultivated Oryza (rice) compared to other sympatric bunting species. Conversely, other bunting species shared a highly similar diet. Furthermore, wild grasses, such as Echinochloa and Digitaria, were identified as major food sources for migrating buntings. Individual variations in dietary composition were observed between conspecific Yellow-breasted buntings. Morphological measurements such as wing length, tail length, weight and the amount of fat stored were found to have limited influence on these variations. Knowledge of the dietary requirements of buntings will be useful to inform future conservation programmes.

The second study focused on identifying the dietary compositions of five common resident bird species in secondary forest in Hong Kong, including the introduced Huet’s Fulvetta (Alcippe hueti), Silver-eared Mesia (Leiothrix argentauris), Red-billed Leiothrix (Leiothrix lutea), Rufous-capped Babbler (Stachyridopsis ruficeps), and native Swinhoe's White-eye (Zosterops simplex). A total of 107 faecal samples were analyzed using DNA metabarcoding with three markers (18S, ITS2 and trnL) while an additional 48 samples were examined for seed germination experiments. The results revealed that the diets of these birds mainly consisted of a diverse range of plants and a limited amount of invertebrates. Their diets and seed dispersal services were highly overlapping. However, seasonal variations were observed in the diets of forest birds, which were closely associated with the fruiting phenologies of plants. Additionally, it was found that these birds were seed dispersers for many native shrubs, tree and climber species that exhibit avian dispersal syndromes. Furthermore, ingested seeds generally took a longer time to germinate compared to control seeds extracted directly from intact fruits. Overall, seed dispersal through birds is an important ecological process, knowledge of plant-bird trophic interactions and seed dispersal patterns will shed light on the restoration of secondary forests, and natural succession. This thesis successfully demonstrated the use of DNA metabarcoding to provide fundamental information on the dietary niches of migratory buntings and resident forest birds, as well as their associated ecological functions in Hong Kong. The findings of this study will be valuable for future ecological research and conservation efforts.