Śatapatha Brāhmaṇa ("of a hundred paths") 10.2.2.7

10.2.2.7

atha pakṣayoraratnī upādadhāti pakṣayostadvīryaṃ dadhāti bāhū vai pakṣau bāhubhyāmu vā annamadyate'nnāyaiva tamavakāśāṃ karoti tadyatpakṣayoraratnī upādadhātyaratnimātrāddhyannamadyate

Two cubits he gives to the two wings: he thereby lays strength into the wings. And the wings are (the bird's) arms, and by means of the arms food is eaten: it is thus for the sake of food that he gives them that space; and when he gives two cubits to the two wings, it is because food is taken from the distance of a cubit.