Why would birds fall from the sky due to a lack of moisture?

Question

Chapter 2 of François Rabelais's novel Pantagruel contains the following passage (quoted from the edition on Wikisource, emphasis added):

Car il ny avoit arbre sus terre quil eust ny feuille ny fleur, les herbes estoient sans verdeur, les rivieres taries, les fontaines à sec, les pauvres poissons delaissez de leurs propres elements vagans et cryans par la terre horriblement, les oyseaulx tumbans de lair par faulte de rosee, les loups, les regnars, cerfs, sangliers, daims, lievres, connils, bellettes, foynes, blereaux et aultres bestes l’on trouvoit par les champs mortes la gueule baye.

In the translation by Thomas Urquhart and Peter Antony Motteux, this passage reads as follows:

The grass was without verdure or greenness, the rivers were drained, the fountains dried up, the poor fishes, abandoned and forsaken by their proper element, wandering and crying upon the ground most horribly. The birds did fall down from the air for want of moisture and dew wherewith to refresh them. The wolves, foxes, harts, wild boars, fallow deer, hares, coneys, weasels, brocks, badgers, and other such beasts, were found dead in the fields with their mouths open.

Note that "wherewith to refresh them" is an addition by the translators. Does this translation correctly represent what Rabelais had in mind or is the description in Pantagruel based on a different kind of assumption? In other words, is the passage based on the assumption that birds refresh themselves with moisture from the air or that they need to moisture for something else?

Answer 1

According to the French philosopher and historian Étienne Gilson, the explanation that the birds use the air's humidity as a source of water is implausible because in that case, they wouldn't take flight in the first place. Gilson points out that according to Aristotelean cosmology and medieval scholasticism, birds fly in a zone situated between Earth and pure air. He refers to Book 1, Part 9 in Aristotle's Metereology, where this zone is described as follows (quoted from E. W. Webster's translation):

(...) It is the region common to water and air, and the processes attending the formation of water above take place in it. We must consider the principles and causes of all these phenomena too as before. The efficient and chief and first cause is the circle in which the sun moves. For the sun as it approaches or recedes, obviously causes dissipation and condensation and so gives rise to generation and destruction. Now the earth remains but the moisture surrounding it is made to evaporate by the sun's rays and the other heat from above, and rises. But when the heat which was raising it leaves it, in part dispersing to the higher region, in part quenched through rising so far into the upper air, then the vapour cools because its heat is gone and because the place is cold, and condenses again and turns from air into water. And after the water has formed it falls down again to the earth.

Part 10 then discusses dew:

Some of the vapour that is formed by day does not rise high because the ratio of the fire that is raising it to the water that is being raised is small. When this cools and descends at night it is called dew and hoar-frost. (...)

Birds fly in the zone where dew and other humid vapours circulate. The zone above this one is closer to the "fire" (in Aristotelian cosmology), where neither clouds nor birds are ever seen. It is as if birds were unable to fly in a type of air devoid of humidity, Gilson adds.

Gilson then turns to Augustine's treatise on the literal interpration of Genesis (De Genesi ad litteram, Book 3, Chapter 2 and other passages), in which the church father writes that the humid vapours make the air "thicker" and thereby create the sort of resistance that makes the flight of birds possible. Apparently, for Augustine, this was a well-established doctrine that served to explain Genesis 1,10 (emphasis added):

And God said, Let the waters bring forth abundantly the moving creature that hath life, and fowl that may fly above the earth in the open firmament of heaven.

For Augustine, only the presence of water (humidity) in the air could explain this passage from Genesis. It is not clear whether Rabelais used Augustine directly as a source or whether he had read one of his medieval commentators. For Gilson, the theory explains perfectly why birds would fall from the sky during a prolonged period of drought that would evaporate most of the humidity in the air.

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References:

• Aristotle: Metereology. Translated by E. W. Webster. The Internet Classics Archive.
• Gilson, Étienne: "Des oiseaux qui tombent faute de rosée", Revue du Seizième siècle, volume 12 (1925), pages 409–411.

(I have been unable to find an online translation of Augustine's De Genesi ad litteram.)