Telugu has a very rich literary tradition, starting in the 11th century CE.
Although Ranganatha follows the theme of the Valmiki Ramayana, he still made changes in some incidents which effects the course of events.
Ranganatha added some significant incidents to make the theme more natural and reliable.
For example, when the bridge was built, a squirrel thinks that it should help Sri Rama to achieve his end; it dips in the sea water, rolls down in the sand and gets rid of the sand in the middle of the rocks under construction.
Knowing this, Sri Rama blesses squirrel for its devotion and draws three lines on its back with his fingers.