Foraging Dynamics, Dietary Preferences, and Niche Specialization of Two Bulbul Species in Sri Lanka’s Dry Zone

Two widespread bird species in Sri Lanka’s dry zone, Pycnonotus cafer (Red-vented Bulbul, RVBB) and Pycnonotus luteolus (White-browed Bulbul, WBBB), were studied to understand their foraging dynamics and ecology. The research was conducted from October 2022 to February 2023 in Mihintale Sanctuary (80.30'11.24"E, 8.21'04.63"N) and the Faculty of Applied Sciences, Rajarata University of Sri Lanka (80.502206"E, 8.353090"N). Data were obtained through focal sampling, opportunistic observations, and mist netting. Both species predominantly foraged on twigs, using gleaning as the dominant food-handling technique. RVBB foraged mostly at the canopy level, while WBBB foraged primarily at the sub-canopy level. Fruits constituted the major food type for both species. RVBB and WBBB utilized 10 and 7 plant species, respectively, with Grewia helicterifolia being the primary foraging plant. Minimal foraging was observed on Croton sp. (RVBB) and Hugonia mistax (WBBB). The correlation between nutritional components and the consumption of both species revealed a preference for foods with lower protein, higher fat, and ash content. There was no linear correlation between gape width and fruit size (r = –0.21, P = 0.69) for both species. The standardized dietary niche breadth indicated both species are specialists, with a high pairwise dietary niche overlap (0.9854). These findings highlight the niche-specific foraging adaptations of RVBB and WBBB within Mihintale, emphasizing their distinct strategies in utilizing plant species, fruit sizes, and foraging heights. Understanding such ecological dynamics is essential for habitat conservation efforts and ensuring the availability of key foraging resources for these species in the dry zone.