While it may feel like Rock Pigeons and House Sparrows are the only birds in town, the world's cities host over 2,000 bird species which is one-fifth of all known species. Research shows that species with the greatest urban success tend to be smaller and less territorial, less picky about foods and nesting locations, lay more eggs, and are longer lived.
Other studies on urban bird populations found that non-migratory, resident city birds had smaller eyes resulting from the brightness in their environments, and that cities can create small, isolated and genetically distinct subpopulations of birds.