These stored chemicals are poisonous to birds and make them sick. Once birds like the blue jays have eaten this butterfly and felt sick they quickly learn never to eat it again. They won't even feed on butterflies that are similar in appearance. The viceroy butterfly has adapted its body to look like the monarch butterfly. By looking similar to the monarch, it tricks birds into thinking it is poisonous.
Birds learn quickly to avoid certain types of food that are poisonous.
Crows are intelligent birds and are difficult to trick. In some areas crows damage crops and people try to shoot them. One person tried to trick the crows into thinking he was not going to shoot them. He walked by their roosting site carrying a broomstick. The broomstick handle looked like the barrel of a shotgun.