PURPORT

According to Sridhara Svami, the ruru is also known as the bhara-srṅga (ati-krurasya bhara-srṅgakhya-sattvasya apadesah samjna). Srila Jiva Gosvami confirms this in his Sandarbha: ruru-sabdasya svayam muninaiva tika-vidhanal lokesv aprasiddha evayam jantu-visesah. Thus although rurus are not seen in this world, their existence is confirmed in the sastras.