Valmiki Ramayana Kishkindha Kanda Sarga 28 Shloka 35

सुरेन्द्रदत्तम् offered by lord of gods, Indra, मुक्तासकाशम् like pearls, पतत् while falling, सुनिर्मलम् exceedingly pure, पत्रपुटेषु in leaf cups, लग्नम् collected, सलिलम् water, तृषिताः thirsty ones, विवर्णच्छदनाः with faded wings, विहङ्गाः birds, हृष्टाः rejoice, पिबन्ति are drinking.

'Thirsty birds rejoice drinking exceedingly pure water held in leafcups offered by Indra (in the form of rain), which looks like pearls collected in the leafcups. As the drops fall on them the hue of their wings seems to change (fade).