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The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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Horizons Of Birds and Beetlejuice
It happened so fast that he barely noticed. One minute Jack Dumbacher was untangling another bird ensnared in a mist net in New Guinea. The next, his career had been hijacked by an exotic poisonous fowl. The hooded pitohui struggling in his hand would soon put Dumbacher, now curator of Ornithology and Mammalogy at the California Academy of Sciences, on the trail of a strange biotoxin. Along the way, he would come to depend on the traditional lore of New Guineans to find the answers. But in the summer of 1989, as he tugged and sweated over the furious black-and-orange bird, that was still all in the future. Dumbacher was in New Guinea studying birds of paradise. In hopes of capturing a few birds for his experiments, the University of Chicago graduate student had set up mist nets throughout the forest. Plenty of unwanted species ensnared themselves as well, including the jay-sized pitohui now fouling the lines. As Dumbacher worked to free the bird, its sharp beak and claws scratched his hand. The scratches stung, but with 39 other nets to check, he had no time to stop for first aid. So he stuck a finger in his mouth to lick the cuts clean-and felt his lips began to tingle and burn. Dumbacher chalked up the sensation to the mix of sweat, dirt, and mosquito repellent on his hands, but the numbness persisted into the night. Days later, after he had nearly forgotten about the episode, a coworker mentioned feeling the same tingling and numbness. When Dumbacher asked what he'd been doing, his coworker answered that he'd been handling pitohuis. "That's when I started to wonder if there was something strange about this bird," Dumbacher says. When he returned to New Guinea the next year, he remembered to pluck a feather from the first pitohui to crash into his webbing. Following time-honored scientific tradition, Dumbacher tested his theories on himself, gingerly putting the feather into his mouth. "It definitely made my mouth tingle and burn," he says. Dumbacher soon discovered that the bird's noxious qualities were well known to local people. "They said, 'ah, they're rubbish birds, you can't even eat that bird. It buggers up your mouth if you try.'" He also learned that people handling the birds often sneezed and got teary eyed. Soon afterward, Dumbacher drove to the airport to pick up his advisor, ornithologist Bruce Beehler of the Smithsonian Institution. While on the road to their field headquarters, Dumbacher mentioned that he had tasted the pitohui's feathers and found them poisonous. "Bruce looked at me and said, 'turn the car around. This is going to be on the cover of Science.' He said he had never heard of a poisonous bird, and that this was big news that would overshadow the other work we were doing." Back in the capital, Port Moresby, the scientists obtained permits from the government to collect a few pitohui. They sampled feathers and other tissues from three of the five known species of pitohui, and took the material back home to the United States. Dumbacher began asking chemists if anyone was willing to look for poisons in his pitohui samples. Most were openly skeptical, and refused. Dumbacher was on the verge of giving up when he happened to pass a few pitohui feathers around for tasting at the end of a talk. Their peculiar properties ultimately led to the feathers landing in the laboratory of National Institutes of Health chemist John Daly. "It took him a long time to get to it," Dumbacher says. "Then one day I got a call and he was really excited. He said, 'Look, you've gotta get me more of those samples because they're really toxic'." Extracts from the feathers injected into laboratory mice caused the animals to go into convulsions and die. After several false starts, the chemists were able to purify the toxin enough to study it. Daly took one look at the readout and realized it was strangely familiar. The poison was batrachotoxin (BTX), an extremely deadly substance that Daly himself had first identified more than 20 years earlier. But those samples had come from the other side of the world, in the skin of poison dart frogs from Colombia. As Beehler had predicted, the announcement of the world's first documented poisonous bird landed Dumbacher's first scientific paper in the pages of Science. Dumbacher, however, continued to puzzle over the case. How could the same rare poison be present in both bird and frog? Earlier research into poison dart frogs provided a few clues. For one thing, the frogs didn't seem to manufacture their own toxins. Those taken from the wild slowly lost their toxicity; those born in captivity contained no batrachotoxin at all. But when BTX was added to their diets, the frogs not only showed no ill effects, but recharged their chemical defenses. But attempts to track the source of frog toxin ground to a halt as political turmoil in Colombia made the rainforests too dangerous to visit. Discovering the poison in pitohuis restarted the quest. On pitohuis, the toxin seemed to be concentrated mostly in the skin and feathers, with far less in the organs and muscle. The amount of toxin also varied tremendously among individuals as well as different pitohui species. Dumbacher concluded that pitohui, like poison dart frogs, gathered their BTX from the environment. Very little was known about the habits of pitohuis, and Dumbacher continued to return to New Guinea each year to follow the poison's trail. New Guinea is a country still close to its tribal roots. Much of its population still relies on the forest to provide food and shelter. Traditional knowledge of the natural world remains strong. At nearly every village Dumbacher visited, local people recognized the birds as inedible. Some even had a taboo against eating them, but no longer remembered why. Others observed special customs surrounding pitohui cookery. "They said if you kill a pitohui, then you should hold it in your hands and cry for it as if it's your own baby. And if you cry long enough and sincerely enough, then you can eat it. And if you didn't cry enough, then it'll make your mouth burn," Dumbacher says. He interprets the story as a way to explain why some pitohui are edible while others are not. Talking with local villagers helped Dumbacher make a second important find. "I would go up to places and say, I'm interested in working with your village and we want to study poisonous birds. In a couple places, the local folks said, well, which poisonous birds are you interested in? And I would say, 'Well, which ones do you have?' Often they would point out a bird called the blue-capped ifrita, and in some cases they said it was even more poisonous than the pitohui." Once again, the New Guineans were right. Lab tests showed the Ifrita kowaldi, with sapphire-blue scalp plumage, could contain even more toxin than the pitohui. Dumbacher now began to wonder why these birds carried such potent chemical weapons. Again, poison dart frog research gave him a head start. BTX is a broad-spectrum toxin, one that affects "pretty much everything that has a central nervous system, from earthworms right up to human beings," Dumbacher says. Traditional hunters in the Amazon smear the poison on their blow darts; one scratch is enough to kill a full-grown howler monkey. Lab tests indicate BTX is up to 250 times deadlier than strychnine. BTX is classified as a neurotoxin. It halts the electrical impulses that travel along the length of each nerve. Normally, these signals are propagated by sodium channels that allow electrically charged ions to move across cell membranes. BTX freezes the channels open, halting the transmission of body messages. Its effects can range from temporary numbness to muscle paralysis and even death. Dumbacher guessed that the toxin might protect the birds from predators. The two most poisonous pitohuis, the hooded (Pitohui dichrous) and variable (Pitohui kirhocephalus), were the most colorful of the tribe. Species from the monarch butterfly to the spotted skunk use conspicuous coloration to warn predators away from the noxious meal ahead. And the fact that the poison was largely on the outside of pitohuis, concentrated on the breast and belly, suggested it might rub off on vulnerable young. Dumbacher decided to test the predator repulsion hypothesis on a common hunter of New Guinea birds: the green tree python. He swabbed downy chicken hatchlings with enough BTX to mimic the dose on a pitohui, and dropped them in the cages of captive pythons. The results were telling. Each snake would slither down from its branch, seize a chick in its mouth, and begin to swallow. Then an extraordinary thing would happen, Dumbacher says. Once the chick was halfway down, the snake would stop cold. "The snake would wrap its body back around the chick and actually pull it out of its mouth. Which is kind of a difficult thing to do, because snakes' teeth bend backwards, and eating is usually a one-way process." Each snake then rubbed its head on other objects and frothed at the mouth. A second test of BTX on feather lice, a common bird parasite, produced a similar result. The lice spent far more time on nontoxic feathers from other birds than on pitohui plumage. The very presence of pitohui feathers was enough to shorten the lives of the lice. But predator defense might not be the only explanation for the phenomenon of poisonous plumage. "Just because the toxin may have a chemical defense function now doesn't mean it evolved that way," Dumbacher says. "The birds may have just evolved resistance to the toxin and that allowed them to eat something nobody else could eat. That would have been an advantage. It could be the way they deal with the toxin is to put it someplace innocuous like their feathers. And later, it worked out to be a chemical defense." All that remained was to find the source of the toxin. But the rainforests of New Guinea are some of the least known, and biologically rich, places on Earth. The creature responsible for BTX could be anywhere. Then Dumbacher had yet another stroke of luck. He was back in New Guinea with an intern in 2002 collecting more bird samples. They had been robbed several times, and since Dumbacher now had to leave, he was worried about his young assistant. Trying to think of a safe place for the young man to work, he remembered Herowana. Herowana is a village of about 1,000 people nestled amidst the forests of New Guinea's Crater Mountain Wildlife Area. Dumbacher had collected birds there back in 1995. It's a remote spot, a two-day walk or more to the nearest road. Says Dumbacher, "The terrain is rugged, and the lifestyle very traditional. People still live in grass thatch houses with all of their extended family." When the student arrived, "They said 'Oh, we're so excited you came back. Because we've figured out where the toxin comes from and we've collected a whole bunch of them for you.'" With that, village elder Avit Wako handed the intern a few glass vials that Dumbacher had left behind. Inside were bright orange beetles no bigger than a rice grain, capped with iridescent purple wing covers. Their sides were nubbled with bubble-like vesicles. Older village men knew the beetles as nanisani. The villagers also called the blue-capped ifrita by the same name. "When pressed on it, they said nanisani means bitter, but it's actually the specific kind of tingling sensation you get from tasting the beetle and tasting the bird," Dumbacher says. The men said they often saw the beetle while cutting kunai grass to thatch their houses. "If it flies into your eyes, they said, phew, will you be in pain." Captured bugs were tucked into a vial that was carefully labeled with the collector's name, the date, and the capture location-just as Wako had observed Dumbacher doing years ago. At first glance, the beetles seemed unlikely carriers of such a potent cocktail. Entomologists back at the Bishop Museum in Honolulu identified them as melyrid beetles, from the genus Choresine. Melyrid beetles are known to occur worldwide. But no one had ever reported finding toxins in melyrids before. Dumbacher turned again to chemist John Daly. Daly's lab crushed the beetles, washed them in solvent, and ran the enriched liquid through a battery of tests. Immediately, their printers began tracing the familiar peaks and valleys of BTX. Now the scientists had to establish a link between the beetles and the birds. The scientists decided to look for beetles inside pitohui and ifrita stomachs. Dumbacher had his doubts. "You look at these little choresine beetles and you think, would a pitohui even bother? They're so small." But at least one Choresine beetle turned up in 49 bird stomachs, evidence the insects were on the menu. "These beetles are toxic enough that you don't have to eat a whole lot of them to be poisonous. It might be that you run across a nest of these things and you fill yourself If the toxins stay in the birds for a long time, they might only need to eat a few a week or a year in order to have this phenomenon of toxicity," Dumbacher says. Dumbacher, Daly, and colleagues reported their findings in the Proceedings of the National Academy of Sciences this fall. Their study revealed that the beetles, like the birds, are probably gathering BTX from a third source in the environment. Dumbacher plans to continue his search for the final source of the toxin. Perhaps one of the villagers in the lush landscapes of New Guinea will know the answer. Kathleen M. Wong is Senior Editor of California Wild. |
