Sparrow Decline Linked to Urban Noise Levels: Those who believe we don't affect the environment around us need to be quieter in their dissent. Research indicates urban noise is limiting communication between parent birds and their chicks. The lack of communication is possibly a key cause of declining sparrow populations.
Without this communication link the sparrow parents aren't feeding the chicks as often, and thus the babies often have a lower survival rate. via The Guradian