There is no compulsive rule that incarnations should occur only on the earth and in human form. Any place and any form can be chosen by the fully free. Whichever place and form promote the purpose of fulfilling the yearning of the devotee, that place and form are chosen by the will of God. God is above and beyond the limits of time and space. He is beyond all characteristics and qualities, and no list of such can describe Him fully. For Him, all beings are equal. The difference between man, beast, bird, worm, insect, and even a god is but a difference of the ‘vessel’ (upadhi). The one single God activates every vessel and gives rise to manifold consequences. God appreciates the consciousness of unity as the basic motive of acts. He doesn’t appreciate the activity itself being one without variety; activity must be suited to the various needs.

- Bhagavatha Vahini, Ch 1, 'The Bhagavatha'.