Legend has it that skulking on Austalia’s forest floors is a bird which forages for earthworms by farting. The hapless worms are so startled by the sensory assault of a Bassian thrush’s fart that their dismayed writhing puts them in mortal danger. Following a quick toot, the gaseous bird simply plucks whichever vermiform vittles volunteer themselves from their humic harbour.
Today, for those who believe this marvel of natural history, the world becomes a little less magical.
Having incorrectly answered a trivia question on Bassian thrush farting, I was recently moved to fact-check this suspect nugget. My initial searches found nothing but a few webpages referring to one another, a book without citations, and nowhere could I find a reference to the primary source. A literature search also turned up nothing useful apart from a 2016 paper describing observations of Bassian thrush foraging ecology, yet there was no mention of the birds venting vapour.
Bassian Thrushes fart while foraging for earthworms. I learned this in a trivia Q the other day. Several websites claim it is truth. Yet I cannot find a primary source for this “fact”. Where does this comes from???
— Michael Whitehead (@Mikey_Whitehead) July 23, 2020
Following a plea to Twitter’s sharpest bird and fart minds, the primary source was soon unearthed for all by Alex Berryman.
It is from Edington (1983): White’s Thrush: some aspects of its ecology and feeding behaviour. South Australian Ornithologist 27: 57—59.
[Knowing taxonomic history helps with searches like this!]
I’m afraid the observation therein is a lot less rigorous than you might hope. pic.twitter.com/beu7nacY8y
— Alex Berryman (@AlexJB497) July 23, 2020
The original observation appeared in a 1983 paper published in South Australian Ornithologist. The reason I couldn’t find anything was that both the bird’s common name and scientific name have changed since the publication of that article.
So what is the evidence that has carried this remarkable phenomenon into Bassian thrush canon? The paper describes a behaviour of dipping the tail (“vent-dipping”), coincident with a noise “similar to a jet of air”. Probing of the soil surface for worms immediately follows. Between vent-dipping, the birds also “shiver”, and whilst shivering there is audible a “very soft sound somewhat similar to an inhalation gasp”. We aren’t told how many birds were observed doing this, and on how many occasions (the paper records 29 total observations of thrushes), so it is up to the reader to decide how common or deviant this behaviour is.
The speculative leap made from this unusual behaviour is that the fart is a strategy to induce the worms to suddenly convulse in repulsion, and reveal their location to the flatulent forager.
From Edington, JSL. 1983. White’s Thrush: Some aspects of its ecology and feeding behaviour. South Australian Ornithologist, 29, pp.57-59.
“The louder of the two noises described (that accompanied by a downward movement of the vent) may well be a ‘scare tactic’ to induce earthworms to contract reflexly (or other prey to move away) and so betray their presence to the Thrush through noise or litter movement and vibration. That these louder noises were made only during foraging, were antecedent to the probing and were more frequent with more intensive foraging, suggests that they were indeed somehow used to detect prey.”
Further, that shivering serves to reload the bird’s cloaca for another blast.
“If the source of the louder noise is assumed to be from the quick passage of air through the vent, then the softer, antecedent noises (each accompanied by a body shiver) might be explained as aerophagia – the gulping of air.”
Now this sphincter-percussion all sounds a bit bizarre, but is not without some scientific precedent. One expert to chime in on Twitter was Dr Dani Rabiotti, author of the book Does it Fart? The Definitive Guide to Animal Flatulence.
It’s generally accepted most birds don’t fart but I guess, similar to some snakes, they could suck air into their cloaca than expel it. I suspect it may just be a myth though – similar to honey badgers farting on bees to subdue them.
— Dr Dani Rabaiotti (@DaniRabaiotti) July 23, 2020
Dani suggests this could be a case of ‘cloacal popping’, or simply a sick bird.
That sounds more akin to cloacal popping, but given it’s observed from a single individual and no one since seems to have seen it, if it was farting it may just have been unwell 😅
— Dr Dani Rabaiotti (@DaniRabaiotti) July 23, 2020
After scratching through the litter of evidence here, I feel it’s time to clear the air. There is simply no compelling evidence that the Bassian thrush uses farts to scare and catch worms. There are some curious but unquantified observations of a bird or birds at one site making some noises that could be due to aspiration and expulsion of air via the cloaca. There are no observations tying this to success in foraging. There have been no subsequent observations supporting the behaviour described in the original paper.
I’m afraid we, as lovers of truth and nature, must let the air out of this myth. Finally, we must all commit from now on, whenever we see a Bassian thrush, to carefully watch its arse, for science.