The eagle (aquila) is so called from the keenness of its eyes (oculi), as Isidore says [can't find citation ]; its sight is said to be so far-reaching and so clear that when it is borne on the air, on still wings, over the ocean, so high that it would hardly be visible to human observers from the ground, from such a height it sees little fish swimming in the sea, and plummeting like a stone it snatches up a fish, and then carries the captive prey to the shore. This bird is naturally hot and dry, eager for prey, and strong and spirited beyond the power of the other birds. Its strength is most powerful in its wings, feet, and beak, for it has wings which are very sinewy and have little flesh on them; it therefore has great endurance for the work of flying. Because it has little flesh compared to the size of its body, and much sinew, on this account it has much strength and power. It is also very feathery, on account of which it is very light.

original latin

Inter omnes autem volucres maxime viget in aquila vis visiva, spiritum enim habet visibilem, temperatissimum, et in actu videndi acutissimum.

Solem enim irreverberatis oculis in suae rotae circumferentia intuetur, et tamen visus sui acies non obtunditur, nec claritate solaris luminis disgregatur, ut dicit Ambrosius.

Dicit etiam Ambrosius, sicut et Aristoteles, quod quaedam species aquilae, quam vocat almachor, est acuti visus valde. Et pullos suos ungue suspensos radiis Solis obiicit et Solem aspicere compellit, et hoc antequam habeant alas completas, et ad hoc eos percutit et vertit ad aspectum Solis. Et si oculus alicuius lacrymetur, ipsum tanquam degenerem vel interficit, vel abiicit a nido, vel contemnit. Si autem directa acie Solis radium viderit, ipsum tanquam in natura sibi similem diligit atque nutrit.

Habet autem aliquas proprietates minus laudabiles. Est enim avis excedens in calore et siccitate, et ideo est animosa et iracunda, quia ira fortis non est, nisi in corporibus magnae siccitatis, ut dicit Aristoteles libro 16, et avibus innocentibus est aquila inimica et infesta. Unguibus enim rapit, et rostro percutit caput avis. Vocem habet roborantem et generaliter omnes aves terrificantem. In aspectu enim aquila et auditu terrentur omnes aves alterius speciei, etiam avea praedae.

Super Psalmos etiam dicit [Augustinus], quod cum senuerit, ita induratur et incurvatur eius rostrum, ut vix possit sumere cibum suum, et contra hoc incommodum invenit remedium, quia petram sibi quaerit, contra quam fortius rostrum percutut et allidit, et sic deponit onus rostri, et cibum capiens, resumptis viribus, iuvenescit.