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Poisonous birds do not have major medical importance, but are interesting and fascinating in their own right. The following data shows how little we actually know of the natural world. In 1989 a researcher (John P. Dumbacher of the National Zoological Park in Washington, D.C), netted a specific bird in New Guinea, named Pitohui dichrous ("rubbish bird", fam. Pachycephalidae). They are the size of a thrush, and both male and female have colored patches in their plumage. After handling a bird, he got scratched. Licking his hands afterwards, he noted numbness of his lips and a burning feeling in his mouth, suggesting the presence of (a) toxin(s). He described it as : "…Within a minute, your tongue tingles, then it burns, and your mouth can go numb for several hours. It's a lot like tasting hot chili peppers or touching a 9-volt battery…." This was very weird, as poisonous birds were unknown at that time. After investigations, it was found that a complex alkaloid toxin, homobatrachotoxin, was concentrated in feathers and the skin of the animals. The concentration varies depending on the species. This toxin is similar to batrachotoxin, the active ingredient in poison dart frogs of Western Colombia (Phyllobates terribilis, P.bicolor and P.aurotaenia; fam Dendrobatidae,). Batrachotoxin and homobatrachotoxin are among the most potent of all naturally occurring nonprotein poisons. Both act on voltage-sensitive sodium channels of excitable tissues, such as nervous tissue, muscle and neuromuscular junctions. Binding of homobatrachotoxin to the sodium channels leads to depolarization of cell membranes due to increased sodium influx. These toxins bind to the sodium channel at a site different than tetrodotoxin and saxitoxin. The hooded pitohui was the first poisonous bird to be identified. Of the three poisonous Pitohui species, the hooded pitohui (Pitohui dichrous) is the most brightly coloured and by far the most poisonous. It is followed by the variable pitohui (Pitohui kirhocephalus) and the rusty pitohui (Pitohui ferrugineus). Depending on their habitat - and, therefore, diet - the crested pitohui (Pitohui cristatus) and black pitohui (Pitohui nigrescens) may be toxic as well. Not much is known about pitohui biology. Major aspects of their life histories remain to be discovered. One of the most important unknown things is how they make homobatrachotoxin. Scientists suppose that the poison derives from something in the birds' diet, as this would explain the discrepancy in toxicity between birds of different species or locale. The levels of batrachotoxins varied widely for different populations of Pitohui, a result compatible with the hypothesis that these birds are sequestering toxins from a dietary source. In captivity, they grow up poison-free. It is possible that insects which form part of the diet, are the original source of the toxin. It is not known how the birds themselves survive the poison in their bodies. The toxin is probably used as a defense mechanism versus predatory snakes and hawks. Similar toxins have also been found in another passerine bird from New Guinea, Ifrita kowaldi, which belongs to a different genus. The genus Ifrita contains only one species. Ifrita kowaldi, a small (30 grammes) blue-capped bird locally known as "bitter bird", lives above 2,000 meters, a higher altitude than the Pitohui species. It concentrates the toxins its feathers and skin. Breathing deeply from plumage of Ifrita induces coughing or allergy-like reactions. The finding suggests that chemical defenses among birds might be more widespread than previously thought.

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Examples of pitohui species

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