This book deals with the study associated to know the incidence and activities of House sparrow, Passer domesticus. House sparrow was abundant in Indian cities including Bangalore long ago. Of late the sparrow population has been declining alarmingly in the Indian cities like Chennai, Delhi, Mumbai, Kolkata and Bangalore region. The populations of the sparrows were observed along the urban-rural gradients in different locations in and around the Bangalore region. This book answers the questions - why the populations of sparrows are declining in most of the city regions. Also, why the populations of sparrows have significant difference in their occurrence along the urban-rural gradients. The reason for the variation was deliberated to know the alarm declining of house sparrow populations. In addition, this book provides an important for the population biology of house sparrow in the ecological point of view.