Aim: To evaluate the patterns of bird assemblage and distribution in an endangered grassland system, taking into accounts both environmental and biotic effects. To further focus on an endangered songbird and associated steppe birds. Location: Inner Mongolia, China Methods: We investigated the relative importance of abiotic and biotic factors driving the abundance and co-occurrence of steppe birds in Inner Mongolia by using joint species distribution models. We examined the general patterns of species assemblage, with a focus on the endangered Jankowski’s Bunting and other species potentially sharing the same niche or interacting with it, including potential competitors (especially the closely-related Meadow Bunting), predators (corvids, raptors) and a parasite (cuckoo). Results: The studied steppe species exhibited varied responses to environmental variables, including climate, landscape and habitat predictors. We observed stronger species correlations due to residual covariates than to abiotic covariates. Jankowski’s Bunting displayed strong positive co-occurrences with other ground-nesting songbirds, and exhibited significant responses to all measured habitat and climate variables, indicating that this endangered bird has a high niche specialization and wide associations with other sympatric steppe bird species. Main conclusion: Our results pointed out that climate, landscape, and steppe habitat predictors are not the only factors structuring bird assemblages. Our results suggested that Jankowski’s Bunting is an indicator of the occurrence of other species, especially open-nesting specialized steppe songbirds, so it could act as a surrogate for overall steppe bird conservation. These findings are helpful for understanding how abiotic and biotic processes interactively alter bird communities and making effective management decisions to mitigate multiple threats to the entire community.