Migratory Blue Tiger butterflies ring in the new

Walking by the backwaters at Aronda, a coastal village near Sawantwadi in southern Maharashtra, we came upon a bush of yellow blooms shimmering with butterflies, mostly Blue Tigers (Tirumala limniace) and a few Common Crows (Euploea core).

Both species are known to migrate extensively during the monsoon, and it was a little surprising to see them here on the West coast of India on New Year's Day. Are they regrouping for the return migration to the Eastern Ghats?

Those in the know please help me with identifying the plant.