6 It is said that the turtle-dove, once separated from her mate, does not contract a new union, but remains in widowhood, in remembrance of her first alliance. Listen, O women! What veneration for widowhood, even in these creatures devoid of reason, how they prefer it to an unbecoming multiplicity of marriages. The eagle shows the greatest injustice in the education which she gives to her young. When she has hatched two little ones, she throws one on the ground, thrusting it out with blows from her wings, and only acknowledges the remaining one. It is the difficulty of finding food which has made her repulse the offspring she has brought forth. But the osprey, it is said, will not allow it to perish, she carries it away and brings it up with her young ones. Such are parents who, under the plea of poverty, expose their children; such are again those who, in the distribution of their inheritance, make unequal divisions. Since they have given existence equally to each of their children, it is just that they should equally and without preference furnish them with the means of livelihood. Beware of imitating the cruelty of birds with hooked talons. When they see their young are from henceforth capable of encountering the air in their flight, they throw them out of the nest, striking them and pushing them with their wings, and do not take the least care of them. The love of the crow for its young is laudable! When they begin to fly, she follows them, gives them food, and for a very long time provides for their nourishment. Many birds have no need of union with males to conceive. But their eggs are unfruitful, except those of vultures, who more often, it is said, bring forth without coupling: and this although they have a very long life, which often reaches its hundredth year. Note and retain, I pray you, this point in the history of birds; and if ever you see any one laugh at our mystery, as if it were impossible and contrary to nature that a virgin should become a mother without losing the purity of her virginity, bethink you that He who would save the faithful by the foolishness of preaching, has given us beforehand in nature a thousand reasons for believing in the marvellous.
7. “Let the waters bring forth the moving creatures that have life, and fowl that may fly above the earth in the open firmament of heaven.” They received the command to fly above the earth because earth provides them with nourishment. “In the firmament of heaven,” that is to say, as we have said before, in that part of the air called οὐρανός, heaven, from the word ὁ ρᾶν, which means to see; called firmament, because the air which extends over our heads, compared to the æther, has greater density, and is thickened by the vapours which exhale from the earth. You have then heaven adorned, earth beautified, the sea peopled with its own creatures, the air filled with birds which scour it in every direction. Studious listener, think of all these creations which God has drawn out of nothing, think of all those which my speech has left out, to avoid tediousness, and not to exceed my limits; recognise everywhere the wisdom of God; never cease to wonder, and, through every creature, to glorify the Creator.
There are some kinds of birds which live by night in the midst of darkness; others which fly by day in full light. Bats, owls, night-ravens are birds of night: if by chance you cannot sleep, reflect on these nocturnal birds and their peculiarities and glorify their Maker. How is it that the nightingale is always awake when sitting on her eggs, passing the night in a continual melody? How is it that one animal, the bat, is at the same time quadruped and fowl? That it is the only one of the birds to have teeth? That it is viviparous like quadrupeds, and traverses the air, raising itself not upon wings, but upon a kind of membrane? What natural love bats have for each other! How they interlace like a chain and hang the one upon the other! A very rare spectacle among men, who for the greater part prefer individual and private life to the union of common life. Have not those who give themselves up to vain science the eyes of owls? The sight of the owl, piercing during the night time, is dazzled by the splendour of the sun; thus the intelligence of these men, so keen to contemplate vanities, is blind in presence of the true light.
During the day, also, how easy it is for you to admire the Creator everywhere! See how the domestic cock calls you to work with his shrill cry, and how, forerunner of the sun, and early as the traveller, he sends forth labourers to the harvest! What vigilance in geese! With what sagacity they divine secret dangers! Did they not once upon a time save the imperial city? When enemies were advancing by subterranean passages to possess themselves of the capitol of Rome, did not geese announce the danger? Is there any kind of bird whose nature offers nothing for our admiration? Who announces to the vultures that there will be carnage when men march in battle array against one another? You may see flocks of vultures following armies and calculating the result of warlike preparations; a calculation very nearly approaching to human reasoning. How can I describe to you the fearful invasions of locusts, which rise everywhere at a given signal, and pitch their camps all over a country? They do not attack crops until they have received the divine command. Or shall I describe how the remedy for this curse, the thrush, follows them with its insatiable appetite, and the devouring nature that the loving God has given it in His kindness for men? How does the grasshopper modulate its song? Why is it more melodious at midday owing to the air that it breathes in dilating its chest?
But it appears to me that in wishing to describe the marvels of winged creatures, I remain further behind than I should if my feet had tried to match the rapidity of their flight. When you see bees, wasps, in short all those flying creatures called insects, because they have an incision all around, reflect that they have neither respiration nor lungs, and that they are supported by air through all parts of their bodies. Thus they perish, if they are covered with oil, because it stops up their pores. Wash them with vinegar, the pores reopen and the animal returns to life. Our God has created nothing unnecessarily and has omitted nothing that is necessary. If now you cast your eyes upon aquatic creatures, you will find that their organization is quite different. Their feet are not split like those of the crow, nor hooked like those of the carnivora, but large and membraneous; therefore they can easily swim, pushing the water with the membranes of their feet as with oars. Notice how the swan plunges his neck into the depths of the water to draw his food from it, and you will understand the wisdom of the Creator in giving this creature a neck longer than his feet, so that he may throw it like a line, and take the food hidden at the bottom of the water.
Source: Nine Homilies of Hexaemeron (New Advent)