What is the theme of "the vain jackdaw"

I'd say that the theme is something like - Borrowed feathers do not make fine birds. In the story, god Jupiter wanted all birds to present themselves before him so that he can choose the most beautiful one to become king of the birds. Jackdaw knew he was ugly which is why he went to the forest and took fallen feathers from more beautiful birds and adorned himself with them to make himself look pretty. In the end, the birds found out about it and he was left ugly and alone. The moral of the story is that you should achieve success based on your own efforts, and not stealing other people's achievements and presenting them as your own.