Irrigation has emerged as a major driver of land-use change in drylands globally, including in India's Thar Desert, where canal and tubewell-based irrigation has transformed vast expanses of arid grasslands into intensive agricultural landscapes. While such transformations are popularly presumed to support greater biodiversity by increasing habitat productivity, their impacts on native bird communities remain poorly understood. In this study, we assessed how irrigation-driven agricultural intensification influences avian assemblages in the western Thar Desert, in a space-for-time substitution framework. We conducted line transect bird surveys during the winter season across three land-cover types - protected grasslands, non-irrigated croplands, and irrigated croplands - and analyzed patterns of species richness, abundance, and community composition using distance sampling, inferential statistics and multivariate ordination techniques. We found that Irrigated croplands supported a compositionally distinct bird assemblage and had significantly higher bird species richness and abundance compared to other land-use types. However, this apparent gain was driven primarily by the proliferation of generalist and mesic species, while desert-adapted insectivores and other habitat specialists showed marked declines. Thus, although irrigation increases bird numbers, it simultaneously threatens native biodiversity by replacing functionally unique desert specialists with widespread generalists. Our findings highlight the need for cautious irrigation planning and offsetting its impacts by protecting remaining natural grasslands.