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On the nutriment and the drink of flyers.
One inquires further into the nutriment of flyers. And first, whether flyers have a big appetite.
It seems not. This is because a cold stomach has a great appetite, but birds have a very warm stomach, and therefore, etc.
Second, one inquires why, when they are nourished by flesh, salty flesh injures them.
And it seems the opposite is the case, since salt cleanses and consumes the feces. But these functions are useful to birds, especially to those with curved talons [ gampsonici], as well as to walkers; therefore, etc.
Third, one inquires whether they only drink a little.
And it seems not, because an appetite for drink is an appetite for the cold and moist. Now, however, birds are particularly warm and dry. Therefore, drink is particularly necessary for them.
Fourth, one inquires why some birds do not raise their necks when they drink until they have finished drinking, and some do.
Fifth, one inquires why birds and fish do not ruminate, as walkers do.
To the first, one must reply that the appetite's intensity arises from the emptying of the stomach. But the stomach's emptying can arise from two causes: in one way, from the consumption of the stomach's contents, as occurs from heat, and in another way from the constriction of those things that are in the stomach, just as occurs from cold. Thus, those who have a warm stomach have a large appetite and can eat a lot, whereas those who have a cold stomach have a large appetite but can only eat a little. Thus, just as fish are gluttonous owing to the coldness of their stomach, so birds have a big appetite owing to their heat.
By means of this, a response to the argument is clear.
To the second argument one must reply that salt is warm and dry and birds are warm and dry. Thus salty flesh intensifies their warmth and dryness, and, owing to this, it is a source of death to them since the heat sharpened by it quickly consumes their moisture. Thus, although salt cleanses and consumes feces, nevertheless it also sharpens the natural heat and introduces dryness. And this is why salty flesh is noxious to birds. It is not noxious to walkers, however, because they have a stronger complexion, etc.
To the third argument one must reply that birds of prey live on raw flesh in which there is a great deal of moisture, and this is why birds like these require less to drink, since the rawness of the flesh tempers their heat. Nevertheless a sparrow hawk [nisus] has been seen which has drunk deeply, but perhaps this occurs in such as these owing to some imbalance resulting from fever, and not naturally.
To the fourth argument one must reply that some birds have a great appetite for drink and have a short neck, and these do not raise their necks before they have drunk, like the doves, sparrows, jackdaws and the like, owing to their gluttonous nature. There are, however, other birds that do not have a great appetite for drink, and ones like this may have a long neck, like the goose and the crane, or a short one, like the birds of prey, and they do raise their necks while drinking, interrupting their drink. Others, like Pliny, say that this is because it is more pleasurable for them to drink this way, and I believe that this is owing to the narrow esophagus in such animals. This is why they raise their necks, in order to gulp their drink more easily.
To the fifth argument one must reply that animals that walk ruminate, but birds or fish do not. There are many reasons for this: because walkers, more so than fish or birds, live off things born of the earth, which are difficult to digest, and this is why they require several digestions, and this is why too they recall the food to the mouth and ruminate. Another reason is that in order for an animal to ruminate it is necessary to retain the food for a long time and chew it well. But birds lack teeth because their weight would impede their flight, which is why they cannot chew. Moreover, should fish retain their aliment in their mouths for a long time, too much water would enter the heart and suffocate them, and this is why wise nature [natura docta] has ordered them to obey the Creator, according to Avicenna in the third book, and not retain the food, which would happen if they ruminated, and this is why, etc.
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