My grandmother used to say that if...

Birds of ill omen — ravens, vultures, crows, owls, and albatrosses — have existed in every culture since the beginning of civilization. This could account for your grandmother’s idea about blackbirds. These omen birds show up in countless stories and folktales. In ancient Rome, an augur — a religious official and fortune-teller — carried a ceremonial standard that featured different birds on either side. The birds on the right were considered good luck, and the birds on the left were bad luck. The standard was used to tell someone’s future.