Abstract

Forest gap dynamics are a key driver of bird community structure. Understanding the effect of forest gaps on abundance and communities is critical in an era of increasing anthropogenic disturbance in tropical forests. In this study, we investigated the impact of natural rainforest gaps on bird communities and abundance in a highly diverse lower montane rainforest in Thailand. We employed mist-netting in a 5-year study (2015-2019) to assess bird assemblages and abundance across paired sites in forest gaps and under closed canopy, resulting in 1,148 captures of 81 species. Total abundance did not differ between forest gaps and under the closed canopy. The long-term study design captured seasonality in bird composition, highlighting dynamic assemblages driven by seasonal migration. We observed a strong effect of forest gaps on bird assemblages. Interestingly, we found Hill Blue Flycatcher (Cyornis whitei) species with a strong preference for forest gaps increased in abundance with total gap size. Most species showed no relationship with forest gap sizes in this area. Our findings support previous research showing that gap sizes of 130–1,020 m² in the lower montane forest are not highly detrimental, yet still reduce bird abundance. This highlights that even moderate habitat disturbances can negatively affect sensitive bird species. Nonetheless, forest gaps may also play a key role in promoting tropical biodiversity by facilitating niche differentiation and specialization among understory birds.

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