Yesterday I said there are no venomous birds. I didn’t say there were no poisonous birds.
Meet the pitohui, the world’s only known poisonous bird. The pitohui, found only in New Guinea, exudes a neurotoxic alkaloid through its skin and feathers, the same toxin found in the poison dart frogs of Central and South America. The poison, which affects both the nerves and the heart, is about ten times more potent than the one found in the fugu blowfish and fifteen times more powerful than curare. But neither the bird nor the frog produce the toxin themselves; they absorb it from the toxic beetles that they eat. And so poison is spread up the food chain: manufactured by a plant for its defense, a beetle gains a tolerance for it and uses the poison for its own defense. Then a bird develops an antidote, and gains the gift. And with this poison, which is in essence a life-preserving agent, comes the gift of color.
The proper name for conspicuous warning coloration is aposematism. It can actually be any signifier: the bitter smell of cyanide in a cherry tree’s leaves, the rattlesnake’s maraca. Toxins are responsible for the flavors of many herbs; the pungent, clove-like scent of basil is a eugenol compound that some bugs find distasteful, while the tannins that give tea its flavor is a phytotoxin meant to protect it from caterpillars. Of course, most medicine that comes from plants is actually a poison meant to kill something else. As much as the world is colored and sweetened by flowers and fruits and mating plumage and the love songs of canaries, it is also colored by toxic butterflies and poisonous berries, the warning cries of parrots and the taste of tobacco. Poison makes the world a far richer and more beautiful place.
Orange is the ultimate aposematic color. For animals with a good eye for color, such as primates and birds, it is the visual equivalent of a crying baby — impossible to ignore. The beetles that produce the alkaloid responsible for the pitohui’s poison are orange, and that orange seems to be contagious. For example, the bird at top, and in the upper right corner of the picture below, is a hooded pitohui. The other three pictured are another species, the variable pitohui, so called for obvious reasons.
The variable pitohui seems to mimic the hooded pitohui’s aposematic coloration. However, both birds are toxic. Why would they need to mimic each other? Couldn’t one just as easily become lime green or fire engine red? This is an example of what’s called Müllerian mimicry, which is slightly but significantly different from Batesian mimicry. Let me explain.
You’ve probably heard of the case of the monarch and the viceroy. The first butterfly, we were told, drinks from the toxic milkweed plant and so makes itself toxic, while the second butterfly gains an advantage by mimicking the first; birds that hate the taste of monarchs wouldn’t be able to tell the two apart. If this were true, it would be a great example of Batesian mimicry. (Another example would be the venomous coral snake and the non-venomous milk snake.) However, it turns out that the viceroy is just as unpalatable to birds as the monarch is — possibly more so. Since both are toxic, they have evolved into one universal symbol: orange and black means do not eat. This is Müllerian mimicry, a mutually beneficial relationship. While a Batesian mimic survives under the wing of its poisonous counterpart, a Müllerian mimic assists its counterpart out by helping to teach predators to avoid a particular pattern. If a raptor eats either a hooded or a variable pitohui and gets sick, it will avoid both variable and hooded pitohuis in the future, since they look the same. Black and orange, then, is not a costume, but an alphabetic letter in a visual language, the “x” in an animalian Esperanto. It means the same thing to snakes, hawks, and humans. One has to wonder what other universal words are spoken out there in the rainforests of New Guinea, and who speaks them, and who listens, and what learns.