Tropical forests support high levels of avian diversity but these areas have been impacted by extensive deforestation. The lowland tropical rainforest of Xishuangbanna in southwest China is one such impacted hotspot. In this region, rubber (Hevea brasiliensis) plantations have replaced most of the original forest, but numerous small fragments of forest remain. To assess the value of these fragments to avian diversity, we classified the fifteen selected remnant forest patches into three size categories, <1 ha, 1–3 ha, and 3–6 ha, and conducted avifauna surveys. We found that 97 bird species inhabit the fragments and that bird diversity increases with patch area. The resident species composition similarity index was low among forest patches, both within and across size categories, and also low between the wet and dry seasons. Ground insectivores, frugivores and large bird species were the most vulnerable to habitat fragmentation. Our study encouragingly shows that fragments can play an important role in bird conservation in regions that now lack large tracts of natural forest; however, current patches are too small to support stable annual populations of some species, while others are more tolerant of fragmentation. We discuss these findings and provide conservation strategies to improve bird conservation within rubber plantations in southern China.