The poet says that the red bird comes to this place to cool his plumes, perhaps by sitting in the slow moving brook, or just by resting in the damp and shade. The bird also comes to "court the flower that cheapens his array." This suggests that the bird is in love with the Rhodora, whose plumes are even lovelier than his own.
If the red bird comes to this "damp nook" to look at the Rhodora and pay court to it, then the bird's relationship to the flower is much the same as the poet's. Both attitudes are responses to the hypothetical sages who ask why the beauty of the Rhodora "is wasted on the earth and sky." The first reply the poet suggests is expressed in the poem's most celebrated line:
Then beauty is its own excuse for Being.
His second thought, however, is that the same power which placed the Rhodora in such an apparently obscure spot was the one that brought him there to love it and write about it. Perhaps the same power also alerted the red bird to the presence of beauty here and brought him to worship the Rhodora. The bird's love of beauty, which leads him to ignore the difference between a plant and an animal, is just as intense as the poet's and leads them both to view the flower in the same way.