Choking is for the weak as far as the ostriches are concerned. Image: OhOlek, Flickr

It's the ostrich's best party trick: no matter how recklessly it gobbles up its food, it probably won't choke. What makes the world's biggest bird such a savvy swallower? The secret is in a small pocket located at the base of its tongue, according to new research.

Dr Martina Crole, a researcher and lecturer in veterinary anatomy at South Africa's Pretoria University, wanted to find out exactly how it's possible for an ostrich not to choke even though it doesn’t have an epiglottis, that handy, flexible little flap that prevents you or me from getting food or water stuck in our windpipes. The ostrich's choke-defying ways are even more unusual given its wide glottis (the opening to the windpipe that channels air to the trachea and therefore needs to be closed during swallowing to prevent choking). 

Getting to grips with the ins and outs of the ostrich's digestive tract required a hands-on approach, which is why Dr Crole spent many a day in her lab with her study specimens manipulating said digestive tracts with forceps (and sometimes her bare hands). What she worked out is that a lot of the action has to do with the tongue.

ostrich open mouth_15_04_2014
The ostrich's anti-choking strategy is all about the tongue. Image: Jaime Juan, Flickr

Just like in humans, an ostrich's tongue moves back towards the throat when it swallows, and the spaces between the vocal folds close. But in the ostrich, it's the tongue (not the epiglottis) that seals the deal. The back of the tongue becomes heavily folded, cradling the glottis (which is situated on an elevated structure called the laryngeal mound). And here's where the special 'pocket' comes into play: the ∩−shaped pocket at the base of the tongue encases the glottis, sealing it off from food and water. And for extra protection, two projections (called lingual papillae) hook over the laryngeal mound. Dr Crole has given this unique anatomical mechanism its own name: the linguo-laryngeal apparatus.

Crole is not the first scientist to discover the ostrich's handy tongue 'pocket' – over the past 200 years, a few other researchers have noticed it, too. But Crole is the first to figure out what it's there for. “[Other researchers] possibly didn’t realise its function because they did not use fresh specimens, but rather opted for material preserved in formalin or alcohol, which hardens the tissue and makes it rather inflexible,” she says. (To get around that problem, Crole ensured her own study specimens were 'fresh' enough to be flexible.) 

And since we're on the subject of ostrich eating habits, Crole has another revelation up her sleeve. She's pretty convinced that while the birds are great at guzzling their food, they (probably) can't taste any of it. 

“It seems ostriches got left out of the loop the day evolution was dishing out taste buds.”

In the context of her work, Crole has already discovered that one ostrich relative, the emu, is quite capable of tasting; that discovery has made her the first researcher to confirm a sense of taste in any ratite species (the group of large, flightless birds to which the ostrich and emu belong). But it seems ostriches got left out of the loop the day evolution was dishing out taste buds. After carefully dissecting, removing and preparing microscopy samples from the heads of ten ostriches and ten emus as part of her research, Crole found no trace of taste buds in the African birds, although only future genetic testing will confirm her findings. 

The lack of taste buds explains why ostriches are pretty undemanding when it comes to diet. "They throw [food] to the back of their mouths, which doesn’t really give them an opportunity to do any tasting,” Crole speculates. “It could also be nature’s way of making it easier for them to eat so-called ‘bad tasting’ food.” 

But what they lack in dietary refinement, ostriches make up for with some of their other – sharper – senses. Crole notes that both emus and ostriches have super-sensitive bills that allow them to 'touch' and inspect objects. Add to that a well-developed sense of smell and great eyesight, and the ostrich is pretty capable of discriminating its food even in the absence of taste. “A good sense of smell is characteristic of the ratites, with kiwis having the best smell of all,” says Crole. “An ostrich’s eye is larger than its brain, and therefore its vision is [also] well developed."

“These findings about ostriches and emus strengthen the case that ratite species should actually be seen as a unique group of birds that [is] very separate from other flying bird species,” she adds.

Top header image: M Kuhn, Flickr