Aristotle's History of Animals In Ten Books · Aristotle
CHAPTER VI.
1. The eagle produces three eggs, of which two only are hatched. This is also related in the poems of Musæus. The bird which lays three eggs, hatches two, and brings up but one. This frequently happens; but three young have been seen in the nest. When the young begin to grow, one of them is turned out by the parent, because she dislikes the trouble of feeding it. At this period it is said to be without food, so that it does not capture the young of wild creatures, for a few days the talons are turned back, and the feathers become white, so that it then becomes cruel to its young. The phene[198] receives and brings up the ejected young one. [198] Vultur cinereus, ossifragus, osprey. 2. The eagle incubates for thirty days; this is the usual period of incubation for large birds, as the goose and the bustard. Moderately sized birds usually sit twenty days, as the ictinus[199] and hierax.[200] The ictinus usually produces two young ones, and sometimes three; the Ætolian kite, as it is called, sometimes produces four. The raven produces not only two, but, as they say, many eggs, which she sits upon for about twenty days. She also turns out some of her young ones. Many other birds do the same thing; and generally those which produce several turn out one.
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