From Ramayana, as presented by Bhakti Vikasa Swami, of this great epos:
Fearing Ravana´s power and seeing him to roam the universe conquering one king after another, the demigods being fearful, assumed animal forms and remained so in hiding. Indra became a peacock, Kuvera a chameleon, Yamaraja became a crow, and Varuna a swan.
Only after Ravana´s departure did the demigods resume their normal features. Indra then gave the peacocks benediction to never again fear snakes. He also made marks on the peacocks, formerly all-blue bodied, to resemble his 1000 eyes. Thus, whenever Indra showers down rain, the peacocks dance as a symbol of their love for him.
Yamaraja gave the crows the benediction to no longer contract the diseases common to other living entities. Additionally, the crows were granted that they would live as long as humans do not kill them. Now when crows are fed, people residing in the abode of Yamaraja become satisfied by that act.
Formerly, swans were not all white. However, by the benediction of Varuna, they became white as a foam and began enjoying great pleasure sporting in the water.
Lastly, Kuvera blessed the chameleon with golden complexion.
Thereafter, the demigods departed for their respective abodes.