An expedition into the jungle of New Guinea has resulted in the discovery of two new species of poisonous birds by researchers. The poisonous birds inhabit one of Earth's most pristine rainforests, a place as exotic as no other in the world. Hearing the words poisonous and bird coupled will be an eye-opener for most. But poisonous birds actually exist. And now, more species have been discovered in New Guinea's jungles. These birds contain a neurotoxin that they can both tolerate and store in their feathers.

These birds contain a neurotoxin that they can both tolerate and store in their feathers

Credit: University of Copenhagen

The other new poisonous bird discovered is the The regent whistler (Pachycephala schlegelii) . Credit: Ian Shriner

The two birds that the researchers discovered to be poisonous are the regent whistler (Pachycephala schlegelii), a species that belongs to a family of birds with a wide distribution and easily recognizable song well-known from across the Indo-Pacific region, and the rufous-naped bellbird (Aleadryas rufinucha).

Most people are familiar with South and Central America's iconic poison dart frogs—especially the golden poison frog. These small, brightly colored amphibians can kill a human at the slightest touch. The discovery of the two new poisonous bird species in New Guinea, which carry the same type of toxin in their skin and feathers, demonstrates that the frog toxin is more widespread than once believed.

The poison in these birds' bodies and plumage is called Batrachotoxin. It is an incredibly potent neurotoxin that, in higher concentrations, such as those found in the skin of golden poison frogs, leads to muscle cramps and cardiac arrest nearly immediately after contact.

The bird's toxin is the same type as that found in frogs, which is a neurotoxin that, by forcing sodium channels in skeletal muscle tissue to remain open, can cause violent convulsions and ultimately death.

Though the level of toxicity of the New Guinean birds is less lethal, it may still serve a defensive purpose, but the adaptive significance for the birds is yet uncertain.

The locals aren't fond of spicy food and steer clear of these birds, because, according to them, their meat burns in the mouth like chili. In fact that's how researchers first became aware of them. And the toxin can be felt when holding onto one of them. It feels kind of unpleasant, and hanging on to one for long isn't an appealing option. This could indicate that the poison serves them as a deterrence of those who would want to eat them to some degree.

According to the researchers, the poisonous birds are an expression of an everlasting evolutionary arms race in nature. It starts at the bottom of the food chain with beetles, insects and other invertebrates. Over time, some of these develop toxicity to avoid being eaten. Perhaps they also acquire a particular coloration that may serve as a warning. This in turn allow them to venture from their hideouts beneath logs and rocks.

There is a distinction in biology between the two ways that animals deploy poisons. There are poisonous animals that produce toxins in their bodies and others that absorb toxins from their surroundings. Like the frogs, the birds belong to the latter category. Both are believed to acquire toxins from what they eat. Beetles containing the toxin have been found in the stomachs of some of the birds. But the source of the toxin itself has yet to be determined.

What makes it possible for these birds to have a toxin in their bodies without themselves being harmed? The researchers studied this with inspiration from poison dart frogs, whose genetic mutations prevent the toxin from keeping their sodium channels open, and thereby preventing cramps.

So, it was natural to investigate whether the birds had mutations in the same genes. Interestingly enough, the answer is yes and no. The birds have mutations in the area that regulates sodium channels, and which we expect gives them this ability to tolerate the toxin, but not in the exact same places as the frogs.

Finding these mutations that can reduce the binding affinity of Batrathotoxin in poisonous birds in similar places as in poison dart frogs, is quite cool. And it showed that in order to adapt to this Batrachotoxin lifestyle, you need some sort of adaptation in these sodium channels".

Therefore, these studies of the birds establish that while their neurotoxin is similar to that of the South American poison dart frogs, the birds developed their resistance and ability to carry it in the bodies independently of the frogs. This is an example of what biologists refer to as convergent evolution.

 Kasun H. Bodawatta et al, Multiple mutations in the Nav1.4 sodium channel of New Guinean toxic birds provide autoresistance to deadly batrachotoxin, Molecular Ecology (2023). DOI: 10.1111/mec.16878

------

How Do Birds Become Poisonous?

Until recently, toxicity in birds had not been described as a trait in birds. It was only in the last two decades that literature started covering this subject.

• Studies have indicated that poisonous birds are rare to find; this also makes them little studied among different bird categories. Poisonous birds obtain toxicity from the animals and plants they consume.
• Data obtained from studies revealed that toxicity in birds is not ancestral. Instead, this trait occurred as a result of evolution. This is especially true for the group of birds classified under Pitohui species.
• Toxicity in these birds is believed to have evolved convergently in some of these bird species. The most striking fact about these birds is that they exhibit unique behaviours attributed to their toxicity.
• For example, the toxic birds under this species tend to be vocal and gregarious. They also lead large mixed bird flocks as they find food in the forest undergrowth. These studies also revealed that the birds considered closest relatives to this species did not possess these behaviours and the toxicity traits.
• Additionally, it was revealed that the toxic Pitohui species tended to be of similar ecology, morphology, and size, which in many ways contributed to their categorization under a similar Genus.
• Interestingly, DNA evidence indicates that the similarity in the toxic Pitohui species can be explained by convergent evolution. This is best described as Mullerian mimicry, which is where the toxic species tend to resemble each other, an ability that is of advantage to them because they end up sharing the cost of communicating to potential predators that they are dangerous.
• The toxins in poisonous birds can also be viewed from an adaptation standpoint. In this regard, it is considered that the poisonous birds have developed histological and/or morphological adaptations for them to produce or store toxins, which is unique to them.

Some other poisonous birds and their toxins:

Hooded Pitohui (homoBTX), 

European Quail (coniine), 

Little Shrikethrush (batrachotoxinin-A), 

Blue-capped Ifrita (batrachotoxins – BTX),

Northern Variable Pitohui (BTX),

Red Warbler (neurotoxic alkaloids),

Spur-winged Goose (cantharidin),

Ruffed Grouse (coniferyl benzoate),

Brush Bronzewing Pigeon (fluorine),

Eurasian Hoopoe (di-methyl sulfide).