On Oahu, Hawaii, there is a white form of the Monarch. This is because two species of birds have been introduced. The two birds are known as the red-vented bulbul and the red-whiskered bulbul. They were introduced in 1965 and 1966. They are now the most common insectivorous birds. They are probably the only birds that eat insects as big as the monarch. Monarchs in Hawaii have low cardiac glycoside levels, but the birds may be immune to the chemical. The two bird species eat the caterpillars and sometimes the chrysalids. They look for them on branches and the underside of leaves in milkweed bushes. The birds also eat resting adults and egg-laying females. They eat flying monarchs less often. The white form has a higher chance of living than the orange one. The white form does not fit the birds' search image of a normal monarch, and so it is not eaten. This kind of defense is known as apostatic selection. The white form is also camouflaged in patches of light shining through groups of leaves.