One of the central issues in avian community ecology is an understanding of diversity patterns. The diversity of birds is especially important in endangered ecosystems because birds are good indicator species, and their presence could give conservation biologists and wildlife managers clues about the overall health of these systems. I studied the richness, abundance, and community composition of songbirds in two endangered ecosystems in temperate North America, riparian willow habitat of the Greater Yellowstone Ecosystem (GYE), and in a restored tallgrass prairie in central Iowa, Neal Smith National Wildlife Refuge (Neal Smith NWR). I was especially interested in the habitat variables across time and space that influenced avian diversity patterns in these two areas. It was also my goal to offer wildlife biologists and managers advice on how to maximize diversity in both endangered ecosystems. Finally, I wanted to emphasize the importance of analyzing flyover data (swallows used as a case study) in order to elucidate further questions about diversity in avian community and landscape ecology. Vegetation height and density were two important variables that help predict avian diversity in both the GYE and at Neal Smith NWR. The age of a restored prairie habitat and litter depth was also very important in shaping the community composition of birds in tallgrass prairies. However, birds respond to different variables in their habitat based on the varying life history characteristics across species (e.g. nesting and foraging preferences), and this makes it difficult to offer general suggestions on how to maximize avian diversity in any natural system. I recommend offering a variety of habitat types and structures in order to attract as many species as possible. It is also critically important to consider the habitat needs of the most endangered birds in each of these ecosystems. Avian biologists should continue to study diversity trends in various systems, and come to a clearer understanding of the specific habitat variables that most influence the richness, abundance, and community composition of birds (habitat features, climate change, patch size etc.).