The works of Ādi Śaṅkarācārya

Sanatsujātīyam

p. 297

p. 297

तत्र ते पक्षिणो भूत्वा प्रपतन्ति यथासुखम् ॥

In plain words

There they take the shape of birds and fly wherever they like.

Close to the Sanskrit

There they, having become birds, fly forth as they please.