1 month, 1 week ago

Birds can't fart. This is a result based on observation, because no one has ever seen birds fart. There is even a view that some gases that should be counted as "farts" will be discharged from the other end of the digestive tract (that is, the mouth) - which may seem common, but scientists haven't figured out yet. 


. In fart, the five components account for more than 99%, which are nitrogen, hydrogen, oxygen, methane and carbon dioxide, and the other components are less than 1%, including the sulfur compounds that give the soul of fart, such as hydrogen sulfide, mercaptan, etc., whose concentration is generally only dozens of PPM. 

The nitrogen and oxygen in fart come from the air swallowed along with food. The hydrogen, methane and carbon dioxide come from the fermentation of intestinal microorganisms, which are the two main sources of fart. In most cases, the gas produced by microbial fermentation is the most important source of fart, which is closely related to the digestion process. 

Let's take a look at the digestive tract of birds. Here's a chicken:


 
 digestive tract of chicken. Crop: crop, proventriculus: glandular stomach, gizzard: chicken gizzard, intestines: intestine, cecum (CECA): cecum, cloaca: cloaca 
 
 
 I guess many people may have been popular science, the digestive tract of people is very long, the small intestine alone is 4-6 meters, and the length of the whole digestive tract is nearly 6 times the height of people. But from the digestive tract diagram of chicken, the intuitive feeling is that it is not that long, which is actually a quite big difference between birds and mammals. 


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 comparison of length of digestive tract and body length in mammals. (although there is no strict sense of herbivores, they still use grass as the main energy source when they occasionally open meat.). 

The structure of the digestive system, the structure of their food and their way of life are highly adaptive. For most birds, flying is the core of their life. Flying consumes a lot of energy and keeps their body light. So most birds eat a large amount of food in total, but the amount of food they eat each time is relatively small. With their very high digestion efficiency, food doesn't need to stay in the digestive tract for a long time, so the digestive tract is naturally shorter. 


. But for insect eating birds, it usually takes more than an hour to digest a chicken flavored crunchy protein, while for mature berry eating birds, it takes only a few minutes. By human standards, a bird is a good straighter. 

The fermentation of microorganisms takes time. For the straight bowed birds, 
 a shorter digestive tract and a faster digestion speed do not leave time for the fermentation of microorganisms, and naturally no gas will be produced 
. 

When some people explain why birds don't fart, they will mention that there is no gas producing microorganism in the digestive tract of birds. In fact, it's wrong to say so. Let's talk about a little bit more. Which gut microbes produce gas? We know that there is an anaerobic environment in the digestive tract. Under such conditions, the end products that will not be metabolized like aerobic respiration are carbon dioxide and water. Specific anaerobes like Clostridium and Bacteroides use carbon dioxide and hydrogen as the end products of metabolism - which explains why farts are flammable. 


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. In fact, most of the air we swallow as we eat is expelled during burping. For birds, in addition to expelling gas, they actually have a unique skill, which is to spit out all the indigestible cellulose, hair, fine bones and so on, so as not to let them enter the intestine. For example, these two balls are spit out by owls:


. On the other hand, they will not be fermented by intestinal bacteria, so they will not produce "fart". Even if a small amount of digestive tract gas is produced, the bird can discharge the gas through the reverse peristalsis of the digestive tract, but this process is not easy to be noticed.

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