In defence of His decision to admit Vibhishana into His camp, Rama narrates a story about a pair of pigeons.
A hunter went to the forest, looking for something to kill for food. But he found no suitable prey. The sky darkened, a strong wind blew and a storm seemed likely to break out.
A female bird, knocked off its perch by the wind, fell near the hunter. He picked it up and put it in a cage and sought shelter under a tree.
He looked up and appealed to the tree for protection against the storm. On the tree was a male pigeon, the companion of the bird the hunter had captured.
As night fell, the hunter began to feel cold. The female bird asked the male bird to help the hunter. The male picked feathers and straw, with which the hunter lit a fire. The male bird felt it was its duty to provide him with food, for he had looked upwards, seeking help.
The hunter had prayed that the tree, with its spreading branches, provide him with shelter, but the birds took his appeal as having been addressed to them too. So the male bird jumped into the fire so that when it was cooked, the hunter could consume it. The birds were not directly asked for help but they were willing to go to the extreme to help out the hunter. This despite the fact that he had imprisoned one of them. The bird gave up the body to which that atheists attach importance, the body which theists know is impermanent, but do not part with willingly, said Navalpakkam Vasudevachariar in a discourse.
Rama narrates the story to show that if a bird were to attach so much significance to the act of surrender, should He too not deem Vibhishana’s surrender significant?
The implication is that had Ravana repented and returned Sita to Rama and surrendered to the Lord Rama, even the demon king would have been forgiven.
The story was also perhaps narrated by Rama to show His angst at not being able to admit Vibhishana at once into His camp because of the objections raised by vanaras.