What do a poison dart frog from South America and a perching bird from New Guinea have in common? Well, both exude neurotoxins that are, gram for gram, some of the most powerful poisons in nature.
That Phyllobates poison dart frogs are highly poisonous is well known – it’s in their name, after all, and a single frog can contain enough toxins to kill more than 10 adult humans in just a few minutes. But that some birds can also be poisonous is something that has only recently been documented by scientists.
How poisonous is the hooded pitohui?
The hooded pitohui (Pitohui dichrous) is thought to be the most toxic of a select few poisonous bird species, all of which are endemic to the forests of New Guinea. The second part of this medium-sized bird’s scientific name, dichrous, means ‘bicoloured’ in Ancient Greek and pertains to its striking, two-tone plumage: a bright sunburst-orange body and a black head, wings and tail.
It has been posited that, just like the poisonous dart frog, its colouration acts as a warning. The plumage shouts “I’m toxic!” to would-be visually guided predators, and sends a message that a mouthful of this bird would be a nasty and distasteful experience.
The toxins themselves belong to a group of highly potent compounds called batrachotoxins. Prior to their discovery in the bodies of these birds, they were only known from some poison dart frog species – hence the name of these toxins: batrachos is Ancient Greek for ‘frog’. In the pitohui, the highest concentration of these alkaloids is found in the skin and feathers.
Why is the hooded pitohui poisonous?
So, where do these birds get their noxious nature from? It seems it’s another thing they have in common with the frogs – the compounds appear to originate from their food.
The batrachotoxins found in Phyllobates frogs aren’t produced by the amphibians themselves, but are borrowed from the insects they hunt among the leaf litter, and the potency varies between populations. In fact, their toxicity dissipates completely when these frogs are taken into captivity and given more convenient live food, such as fruit flies.
Similarly, the toxins in and on the bodies of pitohuis, as well as the other known toxic birds, are also of dietary origin. It’s not by accident that these birds and amphibians share the same chemical defence. Foraging in shared forested habitats, they feed on many of the same species of insect, and the source of their sequestered batrachotoxins seems to be soft-winged flower beetles belonging to the genus Choresine.
The reason for developing toxicity is very much up for debate. In the birds, it is supposed to be much less potent (up to three orders of magnitude less) than that found in the poison dart frogs. Some researchers have seen this as going against the theory that the toxins are used as a defence against predators.
However, one study revealed that lice, mites and other external parasites are put off by the compounds in and on the skin and feathers of the pitohui. Therefore, they might act as a built-in pesticide.
Still, the fact that local indigenous peoples will not eat pitohui, and reports that museum curators handling dead specimens have experienced a numbing sensation, suggests that there may well be some truth in the original theory that the development of this chemical defence is an anti-predator strategy, albeit not exclusively.
