POISONOUS BIRDS MAKE NASTY MEALS

by Whit Gibbons

April 27, 2008

Every animal or plant alive on earth today belongs to a species that successfully evolved over time to protect itself from predators. The means different species have developed to avoid being eaten seem endless; they include camouflage, running away, hiding, and fighting back. Many organisms use toxic chemicals, either venoms or poisons, for defense.

Venomous animals produce a chemical substance in special glands and then inject it into another animal. Injection can be by the spines of a fish, the tail stinger of a scorpion, or the stinging hairs of some caterpillars. In any case, the venomous animal forcibly puts a toxic chemical inside the body of another animal. A poisonous plant or animal produces a chemical substance that is destructive only when another animal touches, smells, or eats the poison. For example, poison ivy produces an oily substance that causes blisters to some people upon contact with the leaves, stems, or roots. Death angel mushrooms and poison hemlock produce chemicals that are harmful to people who eat them. Common garden toads secrete distasteful toxins from skin glands. Although not technically poisonous, the gland-produced chemical delivered by skunks creates a potent smell that would deter any sensible predator. Birds were not known to use chemical warfare for defense until a discovery was published in the early 1990s that added birds to the list of poisonous animals.

No venomous birds have yet been discovered and presumably none exist. But at least three species of New Guinea birds called pitohuis have poisonous skin and feathers. The chemical composition of the poison is similar to that found in the skin of dart poison frogs of Colombia, South America. Dart poison frogs secrete a toxic chemical that makes them unpalatable to other animals. The toxic material is a type of alkaloid that, if eaten or injected, has an immediate effect on the nervous system. Colombian natives use the poison on the tips of darts and arrows used to hunt prey.

The particular toxin of the New Guinea pitohuis was previously unknown anywhere else in the animal kingdom except in one group of animals--the poison frogs. The chemical is a powerful deterrent, and poison frogs are known to be avoided as a source of prey by predators. Presumably the poison operates in a similar fashion for the New Guinea pitohuis by discouraging the typical bird predators such as snakes, other birds, and mammals from having an otherwise palatable meal.

The most toxic of the New Guinea birds is the hooded pitohui, a small orange and black bird with a crest like a tufted titmouse. The birds produce a foul smell, which as far as I know is unusual among birds. While collecting and preparing the first discovered specimens of hooded pitohuis, the investigators suffered from bouts of sneezing, along with numbness and burning of the mouth and nasal lining. As is often true with scientific discoveries, the local populace already knew about the phenomenon. A 1977 book on folklore of the Central Highlands Province in Papua, New Guinea, mentions that local residents said the skin of the hooded pitohui "is bitter and puckers the mouth." They referred to it as a "rubbish bird" and advised that it not be eaten "unless it was skinned and specially prepared." (I feel this way about all "rubbish" animals.)

The findings about poisonous birds are significant in several ways. First, any increase in our knowledge of the natural world is of value in raising our intellectual consciousness. Also important is the confirmation that unrelated and geographically separated animals, such as Colombian frogs and New Guinea birds, can independently evolve the same chemical defense. Such discoveries help us better understand the variation and similarities among organisms as well as appreciate the many ways nature has of solving problems.

Finally, a biological phenomenon heretofore undiscovered by modern science delivers the most important message of all. Western scientists have been studying natural history for decades, yet we are a long way away from knowing it all. New traits, new behaviors, new species are still being discovered.



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