Some Birds Use Chemical Defense
The Hooded Pitohui (Pitohui dichrous) is indeed a rare bird. Dumbacher et al. from the Smithsonian Institute reported in 1992 that the distinctive orange and black New Guinean bird has a potent neurotoxin in its feathers and skin, which serves as a defense against predators. Such a protective chemical defense is very rare in birds and the Dumbacher paper was the first to identify an avian toxin. Surprisingly the chemical agent, homobatrachotoxin, is an alkaloid found in the skin of poisonous frogs. It appears that neither the birds nor the frogs make the neurotoxin but probably acquire it in their diet. The hooded pitohui's defense is so good that other birds, which do not possess the toxic agent, mimic the distinctive coloration of the pitohui to fake predators who know to avoid the toxic bird.
Dumbacher and colleagues recently reported another New Guinean bird, the blue-capped ifrita (Ifrita kowaldi), also bears toxic chemicals in its feathers and skin. In all, 5 species in the genus Pitohui and now the Ifrita have been found using a chemical defense mechanism. Several chemical variants of batrachotoxins were identified including three newly identified agents.
How common is such a chemical defense system in birds? No one knows but these studies have opened a new area in avian biology, which is posing new questions about the survival value of avian toxins. It seems that a few birds are using a new trick to keep predators at bay.
(References: Science 258: 799-801, 1992. Proc. Natl. Acad. Sci., USA, 97:12970-12975, 2000.)
Submitted by Pauline Garber