Second bird genus shares dart-frog toxins

Ifrita kowaldi, a blue-capped handful with the tree-poking habits of a nuthatch, concentrates in its feathers and skin the same alkaloids that defend poison dart frogs. This explains why the bird’s plucked carcass can burn a person’s mouth as a chili pepper does, researchers report.

In its feathers and skin, the ifrita concentrates toxins, especially where they might rub off on eggs and the nest. Dumbacher

A pitohoui’s colors might serve as a warning that its feathers carry poisons. Dumbacher

Until recently, ornithologists didn’t realize any birds grew toxic feathers, says John Dumbacher of the National Zoological Park in Washington, D.C. But in 1992, he and his colleagues published the first full-fledged chemical confirmation of a bird toxin, a wicked cocktail in the bright feathers of New Guinea’s Pitohoui genus.

At the time, the alkaloids, called batrachotoxins, had been found in only one other source in nature, the Phyllobates poison dart frogs on the other side of the world—in Colombia and Panama.

Now, in the second analysis of bird toxins, ifritas turn out to employ the same suite of poisons, say Dumbacher and John W. Daly and Thomas Spande, chemists at the National Institutes of Health in Bethesda, Md. Their analysis is scheduled for publication in the Nov. 21 Proceedings of the National Academy of Sciences.

Dumbacher was in New Guinea studying pitohouis when local people told him about the “bitter bird,” the ifrita. Despite the birds’ chemical match-up, the ifritas and pitohouis don’t sprout close to each other on the avian family tree, he says.

Yet their presence on the same island suggests that the birds didn’t separately evolve means to make the same poison. “I find it easier to believe they’re getting it from something they all eat,” he says. That view also fits data showing that toxin concentrations vary among members of each species.

“It’s utterly perplexing and tantalizing to try to figure out where these toxins are coming from,” Spande says. He doesn’t think frogs make the toxin because in captivity, they grow up poisonfree. But in some 20 years of studying frog dinners, Spande and Daly haven’t found a source.

Batrachotoxins sabotage the sodium channels employed by nerve cells. For a poison-dart frog and now the birds, “tolerating these chemicals is a tough feat,” Dumbacher notes.

When the pitohouis report appeared, ornithologists hailed it as the first evidence of a toxic bird. That wasn’t quite fair, Dumbacher now says. Earlier reports of some 13 poisonous birds lay in nonornithological literature.

Biblical tales of Middle Eastern birds that killed gluttonous people have been confirmed by modern medical cases of dogs and people getting sick eating Eurasian quail migrating along certain routes. John James Audubon gave his dog now-extinct Carolina parakeets to find out whether they were poisonous. Those reports, however, don’t provide the detailed examination more recently accorded to chemicals that other organisms use for defense.

The recent analysis confirming that birds use toxins makes sense to May Berenbaum of the University of Illinois at Urbana-Champaign, an authority on chemical warfare between plants and insects. “I’m extremely happy to see this paper because the absence of reports of chemical defense in birds to me seemed to be a curious omission,” she says. “This shows that Daly’s work [on pitohouis] wasn’t a fluke.”

Susan Milius

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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