Karnatakabhashabhushana 3.36

There is the conjunction of -ira with gaḷ- in the domain of address.

There is the conjunction of -ira with the suffix gaḷ- when expressing duality or plurality, in the domain of address.

[As in:] daivaṅgaḷira ["O deities!"],

dēvategaḷira ["O goddesses!"],

māmaraṅgaḷira ["O mango trees!"],

nandanaṅgaḷira ["O celestial groves!"].

Although this could be established by an ablative phrasing such as "-ir after gaḷ-", the mention of "conjunction" [āślēṣa] is intended to express duality and plurality [directly]. Therefore, in some instances, -ir occurs [independently of gaḷ-]: [as in]

naṇṭira ["O relatives!"],

nallira ["O beloved ones!"],

paṇḍitarkaḷira ["O scholars!"],

tāyyirkaḷira ["O mothers!"].