<P> Different forms of sexual selection are possible, including rivalry among males, and selection of females by males . </P> <P> Warning coloration (aposematism) is effectively the "opposite" of camouflage, and a special case of advertising . Its function is to make the animal, for example a wasp or a coral snake, highly conspicuous to potential predators, so that it is noticed, remembered, and then avoided . As Peter Forbes observes, "Human warning signs employ the same colours--red, yellow, black, and white--that nature uses to advertise dangerous creatures ." Warning colours work by being associated by potential predators with something that makes the warning coloured animal unpleasant or dangerous . This can be achieved in several ways, by being any combination of: </P> <Ul> <Li> distasteful, for example caterpillars, pupae and adults of the cinnabar moth, the monarch and the variable checkerspot butterfly have bitter - tasting chemicals in their blood . One monarch contains more than enough digitalis - like toxin to kill a cat, while a monarch extract makes starlings vomit . </Li> <Li> foul - smelling, for example the skunk can eject a liquid with a long - lasting and powerful odour </Li> <Li> aggressive and able to defend itself, for example honey badgers . </Li> <Li> venomous, for example a wasp can deliver a painful sting, while snakes like the viper or coral snake can deliver a fatal bite . </Li> </Ul> <Li> distasteful, for example caterpillars, pupae and adults of the cinnabar moth, the monarch and the variable checkerspot butterfly have bitter - tasting chemicals in their blood . One monarch contains more than enough digitalis - like toxin to kill a cat, while a monarch extract makes starlings vomit . </Li>

The bright colours of some birds are used as a means to attract a mate