Viceroy butterflies are not poisonous but they look just like poisonous monarch butterflies. Which behavior does the viceroy use to deter birds that would otherwise eat it?

Viceroy butterflies use mimicry as a defense mechanism to deter birds from eating them. By resembling the toxic Monarch Butterflies, which are unpalatable to predators, viceroys exploit the learned aversion that birds have toward their poisonous counterparts. This resemblance helps the viceroy avoid predation, as birds may mistake them for monarchs and choose not to eat them.