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.
Source: Nine Homilies of Hexaemeron (New Advent)