Incredible Creatures: You are what you eat - Toxic Beetle-Eating Birds

Hooded pitohui and soft-winged flower beetle. (Catherine Stanley - www.stanleyillustration.com)

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Toxic birds! Yes they exist. If you are not convinced by the saying “you are what you eat”, read on. In this months Incredible Creatures we start in Papau New Guinea, learning about a species of bird that is toxic. Handling this bird would make your hands go numb. We then learn about a species of goose in Southern Africa that you would not want to eat, it too is toxic. There is an entomological theme behind these toxic birds. Some birds also take dangerous dining to a new level, eating toxic insects, but knowing how to do it without getting sick or killed. Welcome to dangerous dining in the avian world.
The Hooded Pitohui – Don’t Touch Me
In 1989, American biologist Jack Dumbacher travelled to the Papua New Guinea bush in search of birds of paradise. He strung up a number of delicate nets between the trees, and one day found several colourful songbirds tangled in them. They were hooded pitohuis (Pitohui dichrous), little black and orange birds with dark red eyes.
As he struggled to free the pitohuis from his nets, they scratched his hands and the cuts hurt more than they should have. He put his fingers in his mouth to dull the pain, but that only made his tongue tingle and burn.
When he asked the locals if they knew anything about this peculiar effect, they knew not to mess with the hooded pitohui – “a rubbish bird”, they said; no good for eating.
Jack flew some pitohui feathers back to the US for further testing. The chemist who tested them found an extremely potent neurotoxin called batrachotoxin. Years earlier the chemist had identified these toxins in tiny poison dart frogs from South America. In high doses these toxins can lead to paralysis, cardiac arrest and death. Gram for gram they are one of the most toxic natural substances known to science. So take the advice of the locals from Papua New Guinea, and don’t be eating (or touching) hooded pitohui.
There are no species of birds capable of making their own poisons. A few species, however, can use the poisons made by other creatures for their own defense. The pitohuis get their batrachotoxins from small beetles called soft-winged flower beetles (Melyridae) they feed on. Most adults and larvae of this group of beetles are predaceous. But many are common on flowers, hence the name. Four colourful species of these beetles, belonging to a genus called choresine, have been found to contain batrachotoxins, which makes birds that are able to eat them toxic. The locals advise against allowing these beetles to touch the eyes or sweaty face, as a severe burning sensation can result. This, oddly enough, has not been well researched. It is hypothesized that species of soft-winged flower beetles in South America could be the source of the batrachotoxins found in the highly toxic poison dart frogs of that region. But this also has not been well studied.
Don’t Cook this Goose
Spur-winged geese occur in wetlands in sub-Saharan Africa. They feed by grazing, mainly on plant matter, and may occasionally supplement their diet with small fish and insects. One group of insects they are known to eat is blister beetles. Blister beetles are called blister beetles for a reason; they contain a chemical, called cantharidin, that they can secrete for their defense. Cantharidin causes blistering of the skin. Cantharidin has been used medicinally to remove warts. For some animals consuming too many blister beetles can be lethal. In some regions blister beetles are a major concern when harvesting and conditioning crops like alfalfa for horses. But for some animals what doesn’t kill them may aid in their survival.
Spur-winged geese are often poisonous because of blister beetles in their diet. The cantharidin they get from the blister beetles is stored within the tissue of the geese, resulting in poisoning should someone eat the cooked goose. Ten mg of cantharidin can kill a human. So when eating waterfowl in southern Africa, don’t cook this goose, or your goose may be cooked.
Defying Dangerous Dining Rules
Many insects produce toxins to protect themselves from predators. And as we have seen, some predators are not killed or made sick by the toxins, but use them to their advantage. Then there are other predators that although they do not acquire toxins from prey for their own purposes, can still feed on animals with toxins by avoiding the toxins. Caterpillars of monarch butterflies feed on milkweed, which contains toxins known as cardenolides. The caterpillars ingest the chemicals which makes the caterpillars and butterflies toxic to predators, hence the bright warning colours of these butterflies. But there are a few birds that can feed on monarch butterflies. One of these is the black-backed oriole, which lives in forests in Mexico. These orioles avoid the poison by not eating the cuticle (skin), where most of the toxins are stored. The oriole uses its sharp beak to slice the cuticle open, and then eats the fat inside. They feed on monarchs in the morning and evening, when the butterflies are too cold to fly. Black-headed grosbeaks also eat monarch butterflies. And when they do the entire abdomen is missing. These grosbeaks do eat the cuticle. However, they prefer male monarchs, who have 30% fewer toxins than do females.
Many birds eat insects, and they can be helpful by eating insects that we consider pests. In most cases nutrition is what the birds are gaining from consuming insects. But birds that are able to sequester toxins from insects for their own protection is something that has not been well studied. I wonder how many other birds out there, particularly those that appear to have warning colours, are dining on toxic insects?
When it comes to eating poisonous insects, one animals poison can help another animal prosper.
Incredible Creatures is a monthly contribution to provide information on some of the common yet often not well known creatures that we share space with in Manitoba and abroad.

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