background birds breadcrumbs brown buff Camouflage camouflaged climate tolerant common common-pest contrast dark ever-expanding populations fauna feeding gray grey house sparrows insect-eaters introduced-species Matthew 10:29 mottled Old-World-sparrows passer domesticus passerine-birds pavement paving pest plump powerful-beaks prolific seed-eaters small social sparrow sparrows textures true-sparrows two-a-penny worldwide-distribution danger dangerous electric electrics Nepal