Are There Any Poisonous Birds?
Firstly, we need to define what we mean by poisonous. There is a distinction between venomous animals who deliver poison through a bite or a sting and toxic animals who are poisonous to humans and other animals when touched or consumed.
Poisonous birds fall into the latter group as there are currently no known species that produce or inject venom but there are some birds that are toxic when handled or eaten. Poisonous birds sequester, or obtain, toxins from the plants or animals they feed on, most commonly from poisonous insects.
There are only a handful of avian species that are poisonous and there has been little research into the causes or wider implications.
Rubbish birds are rubbish
Pitohuis are a family of birds endemic to New Guinea. The skin and feathers of some of them, especially the variable and hooded pitohuis, contain homobatrachotoxin, a steroidal alkaloid and neurotoxin.
Their toxicity of pitohuis has been known to local people of New Guinea for hundreds of years. Pitohui is a Papuan term for ‘rubbish bird’ or ‘garbage bird’ given to it due to its foul smell and inedibility, and in 1895 scientists writing about the birds of New Guinea in The American Naturalist noted it was the only bird that the natives would not eat.
Despite this, toxicity was not a trait associated with the species until 1990 when a biologist who was studying hooded pitohuis reported numbness and burning when handling them.
Jack Dumbacher from the California Academy of Sciences was trekking in the New Guinea bush when he released a pitohui from a mist net and cut his hand. His hand started tingling and so he put the cut in his mouth. Soon his lips and tongue began to burn, a sensation that lasted for hours.
In the interests of science he put a pitohui feather in his mouth and got the same effect. Realising he may have discovered the first poisonous bird Dumbacher started to look into what chemicals were in the pitohui’s tissues.
In 1992 he found that pitohuis contained batrachotoxin concentrated in their feathers and skin, making them the first documented poisonous birds. The same toxin had only been previously found in the Colombian poison dart frog and they only appear to acquire it in the wild. In captivity poison dart frogs are not very poisonous.
It is a rare toxin that attacks the nerves and muscle membranes which causes the tingling and numbness. In high doses it can result in paralysis, cardiac arrest, and even death. Pound for pound batrachotoxin is the most deadly neurotoxin in the world.
Further research by Dumbacher found that poisonous pitohuis do not produce the toxin themselves but get it from the food they eat. Beetles of the genus Choresine are one potential source and have been found in the stomachs of hooded pitohuis.
Blue-capped ifrits and shrikethrushes are two other species of poisonous birds found in New Guinea. Like pitohuis they most likely sequester toxins from choresine beetles and excrete batrachotoxin into their feathers and skin as a defence against predators. Because ifrits almost exclusively feed on insects the theory that they, pitohuis, shrikethrushes, and the beetles obtain the toxin from a third source has been dismissed.
Viagra for the ancients
Spur-winged geese inhabit the wetlands of sub-Saharan Africa and as the name suggests have sharp spurs on the bend of their wings. They are not true geese and sit in their own subfamily, usually aligned more closely with shelducks.
They use the spurs when attacking other waterfowl including other spur-winged geese. A specimen kept in captivity at Slimbridge maintained a territory on the top of a small hill. If other birds tried to encroach upon the territory the goose would attack them so badly that they would often die from their injuries.
Some wild spur-winged geese also have a chemical weapon in their arsenal; the toxin cantharidin. Only spur-winged geese from the Gambia have the toxin, and again, they do not produce the toxin themselves but ingest it from blister beetles, who secrete the poison as a defence against predators. Cantharidin is also secreted by male blister beetles during copulation. Afterwards, the female covers her eggs with it to protect them.
In large doses cantharidin is a poison which can cause severe chemical burns but historically it has also been used as an aphrodisiac. Preparations made from blister beetles cause swelling in the urinary tract which mimics the effects of sexual arousal and can cause prolonged erections. The wife of Augustus Caesar reportedly used cantharidin to entice dinner guests to commit sexual indiscretions, so she had material she was able to blackmail them with.
Spur-winged geese do not appear to use their toxic flesh to discourage predators but if you were to eat a cooked spur-winged goose you would get very sick or even die as just 10 mg of cantharidin can kill a human.
A very common poison
For those who enjoy dining on game birds it may be somewhat of a surprise to discover that quails are also poisonous.
Coturnism is an illness that causes tenderness in the muscles, and rhabdomyolysis, which is the breakdown of skeletal muscle.
Rhabdomyolysis can also occur in people who are crushed by falling buildings; in trying to heal damaged muscles the bloodstream can quickly become clogged with ruptured cells leading to confusion and disorientation and even kidney failure.
The name coturnism derives from the scientific name for the common quail, Coturnix coturnix. The condition has been known for millennia and is mentioned in the Old Testament. Numbers recounts an incident when the Israelites gathered hundreds of quails. “and they spread them all abroad for themselves round about the camp. And while the flesh was yet between their teeth, ere it was chewed, the wrath of the Lord was kindled against the people, and the Lord smote the people with a very great plague.”
There are other historical records of coturnism and it was so common in the Roman Empire that eating quails was banned in the 1st century.
Quail are only ever poisonous during migration and a number of plants have been suggested for the source. Coniine from hemlock was for a long time thought to be culprit but it cannot be responsible for all cases as it does not seed in spring when quails using the western migration route are toxic. Hellebore, and seeds from the yellow-woundwort are other suggestions but more research is needed before the mystery of the poisonous quails is solved.
It is only relatively recently that ornithologists and scientists have started studying toxicity in birds. Other birds known to be toxic include the ruffed grouse from North America and bronzewings from Australia, and the red warbler endemic to Mexico.
Some chemicals extracted from poison dart frogs, which have been studied for much longer, have been found to have medicinal properties. Over time it may be that birds that can potentially kill us may actually help us to survive.