A Bird Calendar for Northern India is a significant ornithological work by Douglas Dewar that provides a detailed overview of the bird species found in northern India throughout the year. The book is structured as a monthly calendar, highlighting the seasonal changes in bird populations, their behaviors, and migratory patterns.Dewar begins by offering insights into the geographical and climatic conditions of northern India, which significantly influence the region's avifauna. He emphasizes the diversity of habitats, including forests, grasslands, wetlands, and urban areas, and how these environments support a wide range of bird species.