The pitohui (PIT-oh-whee) is one of the two known poisonous bird genera, and was the first toxic bird to be recorded. It is native to Papua New Guinea, and its toxicity was discovered in 1989.
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Pachycephalidae
Genus: Pitohui
Species: 6 species in total, listed below
Pitohui species are found throughout most of
Papua New Guinea. They are forest dwellers, and occur in
mountainous and coastal regions. They are among the most common of Papuan
birds.
Pitohuis are about the size of a jay, most often with black and orange or yellow plumage. There is a large range of colouring in the Pitohui kirhocephalus, or variable pitohui. There appears to be little sexual dimorphism – somewhat unusual for such a strikingly coloured bird. The birds have a pungent and lingering odour.
The rubbish bird
Being a very common genus, pitohuis have been known to science for well over a hundred years. Their toxicity was first noted by Jack Dumbacher, a graduate student who was studying the bird of paradise. While freeing a hooded pitohui from a net, it scratched him. Sucking the graze, Jack noticed a numbing sensation in his lips – characteristic of a toxin.
Studying the poisonous bird was no easy task. Most people Dumbacher approached were convinced that he was wrong. Eventually, he took some of the feathers to John Daly, a pharmacologist who had researched the poison arrow frogs of Colombia. Daly extracted some toxins from the feathers and injected them into a mouse, causing rapid cardiac arrest. Bizarrely, the toxins isolated were batrachotoxins (BTX), the same toxins found in the poison arrow frog.
Returning to New Guinea, Dumbacher discovered that the levels of toxicity in the birds varied not only with species, but also with location. Some members of a species were so toxic as to have an effect simply when held, while some in other regions were hardly toxic at all. The toxins are located in the birds’ skin and feathers, and appear particularly concentrated on the breast and underbelly.
Jack Dumbacher sought out tribal leaders, in particular Ian Saem Majnep, who had collaborated on a book about native birds some years earlier, in order to find out more about the pitohui. He learned that the natives had known about the bird’s toxicity for a long time – naming the creature “the rubbish bird”. The only way to eat it, apparently, was to strip off the skin and smear the meat with charcoal – an agent that typically adheres to many poisons – before cooking it.
Don’t eat me!
The toxic nature of the pitohui is an effective protection against predators. The discomfort caused by attempting to eat one would repel most creatures. Anything foolish enough to consume a whole pitohui could well face death (though humans have consumed small amounts of skin with no severe effect).
The bright orange and black colouring of the pitohui is a typical warning to predators, the same as seen on the poison arrow frog. The visual signal that a creature is poisonous creates a learned response in predators, and they eventually avoid creatures with this striking colouring.
In addition, the concentration of the toxins in the breast and underbelly causes the transfer of toxins to the eggs and nest. This provides an especially potent protection against marauding snakes. Snakes typically sense their food through a combination of smell and taste with their flickering tongues – the toxins would certainly repel them. The toxins also appear to repel certain parasites.
Of the 6 pitohui species, only 5 are considered toxic. Of those, the levels of toxin vary greatly, as mentioned above. The most toxic members of the genus are the hooded and the variable pitohuis. As the name of the latter suggests, it is variable. The plumage differs so greatly that over 20 sub-species are known.
Given this example of a range of related birds, some toxic, some not, it is not surprising that researchers are finding examples of both Mullerian and Batesian mimicry. Mullerian mimicry involves several toxic species or subspecies developing similar colouring, and Batesian mimicry has non-toxic creatures developing the markings shown by their toxic relatives.
Subspecies of the variable pitohui differ greatly over their range. In areas where hooded pitohui occur, a variable subspecies may be similar to the hooded species, whereas the same variable subspecies may appear quite different where no hooded pitohui are found. This suggests that mimicry, and not a common ancestor, may be responsible.
Frogs and birds and bugs, oh my!
In studies of the poison arrow frog, John Daly had performed an intriguing experiment. Frogs fed on a non-toxic diet of termites produced non-toxic offspring. Yet, when these frogs matured and were fed small amounts of BTX, the toxin began accumulating normally in their skin. Daly concluded that the toxin was being concentrated from some part of the frogs’ diet – probably an obscure insect source.
Researchers suspect that the pitohui’s case may be similar. The presence of the toxin in the skin and feathers would seem to support this argument, as would the variation in toxicity between members of the same species. A similar experiment to that carried out with the poison arrow frogs is being considered.
Other possibilities have been raised. The toxin could come from a bacterial source, or be of plant origin. It is possible that the bird synthesizes BTX itself, with each chemical component coming from a different source. Experiment, and listening to native tribes who knew of the pitohui’s poison long before westerners discovered it, may well find the answer.
Already, another genus with the same use of the toxin has been located in New Guinea. The blue-capped ifrita (Ifrita kowaldi) was discovered through consultation with native tribes. It, too, shows a variation in toxicity over its range.
Pitohui species:
Pitohui dichrous (Hooded Pitohui)
Pitohui incertus (White-bellied Pitohui)
Pitohui ferrugineus (Rusty Pitohui)
Pitohui cristatus (Crested Pitohui)
Pitohui kirhocephalus (Variable Pitohui)
Pitohui nigrescens (Black Pitohui)
Acknowledgements:
http://www.nationmaster.com/encyclopedia/Pachycephalidae
http://www.curator.org/LegacyVMNH/WebOfLife/Kingdom/P_Chordata/ClassReptilia/O_Archosauria/SubOAves/pitohui.htm
http://www.findarticles.com/p/articles/mi_m1200/is_14_160/ai_79547751
http://listserv.arizona.edu/cgi-bin/wa?A2=ind9712d&L=birdchat&F=&S=&P=5269
http://nationalzoo.si.edu/Publications/ZooGoer/2001/2/intoxnewguineabirds.cfm
http://www.abvt.org/pitohui.htm
http://www.mnh.si.edu/geneticslab/StaffPage/DumbacherJ/jdumbacher.html