Dheer beel, situated in western Assam, India, is a major wetland in the Brahmaputra Valley (Saikia & Bhattacharjee 1993). It is listed as an Important Bird Area (IBA) under the Chakrashila complex (Islam & Rahmani 2004; Fig. 1). The complex includes Chakrashila Wildlife Sanctuary, and Dheer-, Diplai-, and Dakra- beels. Beels are oxbow lakes / cutoff meanders with static water in the Ganges–Brahmaputra floodplains. These lesser-known wetlands are major bird habitats and an important wintering ground for many migratory species. Assam itself is immensely rich in avifaunal diversity with 900 species and subspecies (Choudhury 2000) recorded; roughly half of the 160 species utilizing beels are migratory (Choudhury 2000). Waterbirds can broadly be defined as species ecologically dependent on wetlands. They are a key attribute of these ecosystems, forming vital links in food webs (Kumar et al. 2003). Waterfowl counts also form one of several elements used to identify important wetlands (Wei & Mundkur 2004). Despite the importance of Dheer beel, it remains unprotected. It also lacks a comprehensive checklist of the rich array of residential and migrant avifauna. We studied the winter avifaunal diversity in Dheer from 2005–2007, and recorded 62 species of birds belonging to 17 families. Anatidae had the highest representation (13 species), followed by the Scolopacidae (eight). We compared changes in trends of the species diversity over two winters.